introduction for universe essay

What is the Universe?

The universe is everything. It includes all of space, and all the matter and energy that space contains. It even includes time itself and, of course, it includes you.

Earth and the Moon are part of the universe, as are the other planets and their many dozens of moons. Along with asteroids and comets, the planets orbit the Sun. The Sun is one among hundreds of billions of stars in the Milky Way galaxy, and most of those stars have their own planets, known as exoplanets.

The Milky Way is but one of billions of galaxies in the observable universe — all of them, including our own, are thought to have supermassive black holes at their centers. All the stars in all the galaxies and all the other stuff that astronomers can’t even observe are all part of the universe. It is, simply, everything.

Though the universe may seem a strange place, it is not a distant one. Wherever you are right now, outer space is only 62 miles (100 kilometers) away. Day or night, whether you’re indoors or outdoors, asleep, eating lunch or dozing off in class, outer space is just a few dozen miles above your head. It’s below you too. About 8,000 miles (12,800 kilometers) below your feet — on the opposite side of Earth — lurks the unforgiving vacuum and radiation of outer space.

In fact, you’re technically in space right now. Humans say “out in space” as if it’s there and we’re here, as if Earth is separate from the rest of the universe. But Earth is a planet, and it’s in space and part of the universe just like the other planets. It just so happens that things live here and the environment near the surface of this particular planet is hospitable for life as we know it. Earth is a tiny, fragile exception in the cosmos. For humans and the other things living on our planet, practically the entire cosmos is a hostile and merciless environment.

How old is Earth?

Our planet, Earth, is an oasis not only in space, but in time. It may feel permanent, but the entire planet is a fleeting thing in the lifespan of the universe. For nearly two-thirds of the time since the universe began, Earth did not even exist. Nor will it last forever in its current state. Several billion years from now, the Sun will expand, swallowing Mercury and Venus, and filling Earth’s sky. It might even expand large enough to swallow Earth itself. It’s difficult to be certain. After all, humans have only just begun deciphering the cosmos.

While the distant future is difficult to accurately predict, the distant past is slightly less so. By studying the radioactive decay of isotopes on Earth and in asteroids, scientists have learned that our planet and the solar system formed around 4.6 billion years ago.

How old is the universe?

The universe, on the other hand, appears to be about 13.8 billion years old. Scientists arrived at that number by measuring the ages of the oldest stars and the rate at which the universe expands. They also measured the expansion by observing the Doppler shift in light from galaxies, almost all of which are traveling away from us and from each other. The farther the galaxies are, the faster they’re traveling away. One might expect gravity to slow the galaxies’ motion from one another, but instead they’re speeding up and scientists don’t know why. In the distant future, the galaxies will be so far away that their light will not be visible from Earth.

Put another way, the matter, energy and everything in the universe (including space itself) was more compact last Saturday than it is today.

Put another way, the matter, energy and everything in the universe (including space itself) was more compact last Saturday than it is today. The same can be said about any time in the past — last year, a million years ago, a billion years ago. But the past doesn’t go on forever.

By measuring the speed of galaxies and their distances from us, scientists have found that if we could go back far enough, before galaxies formed or stars began fusing hydrogen into helium, things were so close together and hot that atoms couldn’t form and photons had nowhere to go. A bit farther back in time, everything was in the same spot. Or really the entire universe (not just the matter in it) was one spot.

Don't spend too much time considering a mission to visit the spot where the universe was born, though, as a person cannot visit the place where the Big Bang happened. It's not that the universe was a dark, empty space and an explosion happened in it from which all matter sprang forth. The universe didn’t exist. Space didn’t exist. Time is part of the universe and so it didn’t exist. Time, too, began with the big bang. Space itself expanded from a single point to the enormous cosmos as the universe expanded over time.

What is the universe made of?

The universe contains all the energy and matter there is. Much of the observable matter in the universe takes the form of individual atoms of hydrogen, which is the simplest atomic element, made of only a proton and an electron (if the atom also contains a neutron, it is instead called deuterium). Two or more atoms sharing electrons is a molecule. Many trillions of atoms together is a dust particle. Smoosh a few tons of carbon, silica, oxygen, ice, and some metals together, and you have an asteroid. Or collect 333,000 Earth masses of hydrogen and helium together, and you have a Sun-like star.

For the sake of practicality, humans categorize clumps of matter based on their attributes. Galaxies, star clusters, planets, dwarf planets, rogue planets, moons, rings, ringlets, comets, meteorites, raccoons — they’re all collections of matter exhibiting characteristics different from one another but obeying the same natural laws.

Scientists have begun tallying those clumps of matter and the resulting numbers are pretty wild. Our home galaxy, the Milky Way, contains at least 100 billion stars, and the observable universe contains at least 100 billion galaxies. If galaxies were all the same size, that would give us 10 thousand billion billion (or 10 sextillion) stars in the observable universe.

But the universe also seems to contain a bunch of matter and energy that we can’t see or directly observe. All the stars, planets, comets, sea otters, black holes and dung beetles together represent less than 5 percent of the stuff in the universe. About 27 percent of the remainder is dark matter, and 68 percent is dark energy, neither of which are even remotely understood. The universe as we understand it wouldn’t work if dark matter and dark energy didn’t exist, and they’re labeled “dark” because scientists can’t seem to directly observe them. At least not yet.

How has our view of the universe changed over time?

Human understanding of what the universe is, how it works and how vast it is has changed over the ages. For countless lifetimes, humans had little or no means of understanding the universe. Our distant ancestors instead relied upon myth to explain the origins of everything. Because our ancestors themselves invented them, the myths reflect human concerns, hopes, aspirations or fears rather than the nature of reality.

Several centuries ago, however, humans began to apply mathematics, writing and new investigative principles to the search for knowledge. Those principles were refined over time, as were scientific tools, eventually revealing hints about the nature of the universe. Only a few hundred years ago, when people began systematically investigating the nature of things, the word “scientist” didn’t even exist (researchers were instead called “natural philosophers” for a time). Since then, our knowledge of the universe has repeatedly leapt forward. It was only about a century ago that astronomers first observed galaxies beyond our own, and only a half-century has passed since humans first began sending spacecraft to other worlds.

In the span of a single human lifetime, space probes have voyaged to the outer solar system and sent back the first up-close images of the four giant outermost planets and their countless moons; rovers wheeled along the surface on Mars for the first time; humans constructed a permanently crewed, Earth-orbiting space station; and the first large space telescopes delivered jaw-dropping views of more distant parts of the cosmos than ever before. In the early 21st century alone, astronomers discovered thousands of planets around other stars, detected gravitational waves for the first time and produced the first image of a black hole.

With ever-advancing technology and knowledge, and no shortage of imagination, humans continue to lay bare the secrets of the cosmos. New insights and inspired notions aid in this pursuit, and also spring from it. We have yet to send a space probe to even the nearest of the billions upon billions of other stars in the galaxy. Humans haven’t even explored all the worlds in our own solar system. In short, most of the universe that can be known remains unknown .

The universe is nearly 14 billion years old, our solar system is 4.6 billion years old, life on Earth has existed for maybe 3.8 billion years, and humans have been around for only a few hundred thousand years. In other words, the universe has existed roughly 56,000 times longer than our species has. By that measure, almost everything that’s ever happened did so before humans existed. So of course we have loads of questions — in a cosmic sense, we just got here.

Our first few decades of exploring our own solar system are merely a beginning. From here, just one human lifetime from now, our understanding of the universe and our place in it will have undoubtedly grown and evolved in ways we can today only imagine.

Next: The Search for Life: Are We Alone?

Essay on Our Universe

Students are often asked to write an essay on Our Universe in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Our Universe

What is the universe.

The universe is a vast space that holds everything we know – from tiny atoms to giant galaxies. It includes all of space, time, energy, and matter. Imagine it as a huge home where all the stars, planets, and moons live. It’s so big that we can’t see the end of it, and it’s always expanding.

Stars and Galaxies

Stars are like giant balls of gas that give off light and heat. They group together to form galaxies. Our sun is a star, and it’s part of a galaxy we call the Milky Way. There are billions of galaxies each with its own stars.

Planets and Moons

Planets are big objects that orbit, or go around, a star. Earth is a planet that goes around our sun. Some planets have moons, which are smaller objects that orbit planets. Just like Earth has one moon, other planets can have many.

The Mystery of Space

Space is full of mysteries. Scientists use telescopes to study far-away stars and planets. They’re trying to learn more about black holes, which are places in space where gravity is very strong, and about the possibility of life beyond Earth.

250 Words Essay on Our Universe

The big bang.

The universe began with a huge explosion called the Big Bang about 13.8 billion years ago. This explosion made all the space, time, matter, and energy in the universe. It started very small and hot, then cooled and stretched to become as big as it is now, and it’s still expanding.

Stars are huge balls of hot gas that give off light and heat. Our sun is a star. There are billions of stars in the universe. Stars group together to form galaxies. Our galaxy is called the Milky Way, and it has billions of stars too. There are so many galaxies we can’t count them all.

Planets are big objects that orbit, or go around, stars. Our Earth is a planet. Some planets have moons that orbit them. Moons are smaller than planets and there are hundreds of moons in our universe.

Exploring the Universe

Scientists use telescopes to look at stars, planets, and galaxies. They use space probes to explore things too far to see with telescopes. By studying the universe, we learn more about where we come from and our place in the cosmos.

500 Words Essay on Our Universe

Introduction to the universe.

The universe is like a huge home with many rooms, each filled with stars, planets, and all sorts of interesting things. Imagine looking up at the night sky. Every star you see is part of our universe. It is everything that exists, from the smallest ant to the biggest galaxy.

What’s in the Universe?

The size of our universe.

Think of the biggest thing you’ve ever seen. Now imagine something a million times bigger. Our universe is even larger than that! It’s so big that we measure how far things are in it with a special word: “light-year.” A light-year is the distance light travels in one year, and light is super fast!

The Beginning of Everything

A long time ago, scientists believe the universe started with a big bang. It wasn’t an explosion, but more like everything, all the space, time, and stuff that would become galaxies, started expanding from a tiny point. Since then, the universe has been getting bigger and bigger.

The Life of Stars

Humans have always been curious about the stars. We’ve used telescopes to look far away, and we’ve sent spacecraft to explore planets and moons. Some spacecraft, like the Voyager probes, have even left our solar system and are sending back information from beyond.

The Mystery of Dark Matter and Dark Energy

There are things in the universe we can’t see called dark matter and dark energy. We know they’re there because they affect how galaxies move and how the universe is growing. But what they are exactly is still a big question.

Our Place in the Universe

Even though the universe is so vast, our Earth is just a tiny part of it. But it’s a special part because it’s where we live, and so far, it’s the only place we know that has life. We are still learning so much about the universe and our place in it.

Our universe is a fascinating and mysterious place. It’s full of wonders that we are just beginning to understand. As we continue to look up at the stars and learn more, we realize how amazing it is that we are a part of something so vast and incredible. The universe is the biggest adventure waiting for us to explore.

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• The Universe

The Universe is everything we can touch, feel, sense, measure or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time. Before the birth of the Universe, time, space and matter did not exist.

The Universe contains billions of galaxies, each containing millions or billions of stars. The space between the stars and galaxies is largely empty. However, even places far from stars and planets contain scattered particles of dust or a few hydrogen atoms per cubic centimeter. Space is also filled with radiation (e.g. light and heat), magnetic fields and high energy particles (e.g. cosmic rays).

The Universe is incredibly huge. It would take a modern jet fighter more than a million years to reach the nearest star to the Sun. Travelling at the speed of light (300,000 km per second), it would take 100,000 years to cross our Milky Way galaxy alone.

No one knows the exact size of the Universe, because we cannot see the edge – if there is one. All we do know is that the visible Universe is at least 93 billion light years across. (A light year is the distance light travels in one year – about 9 trillion km.)

The Universe has not always been the same size. Scientists believe it began in a Big Bang, which took place nearly 14 billion years ago. Since then, the Universe has been expanding outward at very high speed. So the area of space we now see is billions of times bigger than it was when the Universe was very young. The galaxies are also moving further apart as the space between them expands.

Story of the Universe

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Earliest conceptions of the universe

Astronomical theories of the ancient greeks.

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universe , the whole cosmic system of matter and energy of which Earth , and therefore the human race, is a part. Humanity has traveled a long road since societies imagined Earth, the Sun , and the Moon as the main objects of creation, with the rest of the universe being formed almost as an afterthought. Today it is known that Earth is only a small ball of rock in a space of unimaginable vastness and that the birth of the solar system was probably only one event among many that occurred against the backdrop of an already mature universe. This humbling lesson has unveiled a remarkable fact, one that endows the minutest particle in the universe with a rich and noble heritage: events that occurred in the first few minutes of the creation of the universe 13.7 billion years ago turn out to have had a profound influence on the birth, life, and death of galaxies , stars , and planets . Indeed, a line can be drawn from the forging of the matter of the universe in a primal “ big bang ” to the gathering on Earth of atoms versatile enough to serve as the basis of life . The intrinsic harmony of such a worldview has great philosophical and aesthetic appeal, and it may explain why public interest in the universe has always endured.

The “ observable universe ” is the region of space that humans can actually or theoretically observe with the aid of technology. It can be thought of as a bubble with Earth at its centre. It is differentiated from the entirety of the universe , which is the whole cosmic system of matter and energy, including the human race. Unlike the observable universe, the universe is possibly infinite and without spatial edges.

This article traces the development over time of humanity’s perception of the universe, from prehistoric observations of the night sky to modern calculations on the recessional velocity of galaxies. For articles on component parts of the universe, see solar system , star , galaxy , and nebula . For an explanation of the scientific study of the universe as a unified whole, see cosmology . For an article about the possible existence of other universes, see multiverse .

All scientific thinking on the nature of the universe can be traced to the distinctive geometric patterns formed by the stars in the night sky. Even prehistoric people must have noticed that, apart from a daily rotation (which is now understood to arise from the spin of Earth ), the stars did not seem to move with respect to one another: the stars appear “fixed.” Early nomads found that knowledge of the constellations could guide their travels, and they developed stories to help them remember the relative positions of the stars in the night sky. These stories became the mythical tales that are part of most cultures .

When nomads turned to farming, an intimate knowledge of the constellations served a new function—an aid in timekeeping, in particular for keeping track of the seasons . People had noticed very early that certain celestial objects did not remain stationary relative to the “fixed” stars; instead, during the course of a year, they moved forward and backward in a narrow strip of the sky that contained 12 constellations constituting the signs of the zodiac . Seven such wanderers were known to the ancients: the Sun , the Moon , Mercury , Venus , Mars , Jupiter , and Saturn . Foremost among the wanderers was the Sun: day and night came with its rising and setting, and its motion through the zodiac signaled the season to plant and the season to reap. Next in importance was the Moon: its position correlated with the tides , and its shape changed intriguingly over the course of a month. The Sun and Moon had the power of gods; why not then the other wanderers? Thus probably arose the astrological belief that the positions of the planets (from the Greek word planetes , “wanderers”) in the zodiac could influence worldly events and even cause the rise and fall of kings. In homage to this belief, Babylonian priests devised the week of seven days, whose names even in various modern languages (for example, English, French, or Norwegian) can still easily be traced to their origins in the seven planet-gods.

The apex in the description of planetary motions during classical antiquity was reached with the Greeks , who were of course superb geometers . Like their predecessors, Greek astronomers adopted the natural picture, from the point of view of an observer on Earth , that Earth lay motionless at the centre of a rigidly rotating celestial sphere (to which the stars were “fixed”), and that the complex to-and-fro wanderings of the planets in the zodiac were to be described against this unchanging backdrop. They developed an epicyclic model that would reproduce the observed planetary motions with quite astonishing accuracy. The model invoked small circles on top of large circles, all rotating at individual uniform speeds, and it culminated about 140 ce with the work of Ptolemy , who introduced the ingenious artifact of displaced centres for the circles to improve the empirical fit. Although the model was purely kinematic and did not attempt to address the dynamical reasons for why the motions were as they were, it laid the groundwork for the paradigm that nature is not capricious but possesses a regularity and precision that can be discovered from experience and used to predict future events.

The application of the methods of Euclidean geometry to planetary astronomy by the Greeks led to other schools of thought as well. Pythagoras ( c. 570– c. 490 bce ), for example, argued that the world could be understood on rational principles (“all things are numbers”); that it was made of four elements—earth, water , air , and fire; that Earth was a sphere; and that the Moon shone by reflected light . In the 4th century bce Heracleides Ponticus , a follower of Pythagoras, taught that the spherical Earth rotated freely in space and that Mercury and Venus revolved about the Sun . From the different lengths of shadows cast in Syene and Alexandria at noon on the first day of summer, Eratosthenes ( c. 276–194 bce ) computed the radius of Earth to an accuracy within 20 percent of the modern value . Starting with the size of Earth’s shadow cast on the Moon during a lunar eclipse , Aristarchus of Samos ( c. 310–230 bce ) calculated the linear size of the Moon relative to Earth. From its measured angular size, he then obtained the distance to the Moon. He also proposed a clever scheme to measure the size and distance of the Sun. Although flawed, the method did enable him to deduce that the Sun is much larger than Earth. This deduction led Aristarchus to speculate that Earth revolves about the Sun rather than the other way around.

Unfortunately, except for the conception that Earth is a sphere (inferred from Earth’s shadow on the Moon always being circular during a lunar eclipse), these ideas failed to gain general acceptance. The precise reasons remain unclear, but the growing separation between the empirical and aesthetic branches of learning must have played a major role. The unparalleled numerical accuracy achieved by the theory of epicyclic motions for planetary motions lent great empirical validity to the Ptolemaic system . Henceforth, such computational matters could be left to practical astronomers without the necessity of having to ascertain the physical reality of the model. Instead, absolute truth was to be sought through the Platonic ideal of pure thought. Even the Pythagoreans fell into this trap; the depths to which they eventually sank may be judged from the story that they discovered and then tried to conceal the fact that the square root of 2 is an irrational number (i.e., cannot be expressed as a ratio of two integers ).

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Introduction

The universe is also called the cosmos. Cosmology is the branch of science that studies the universe as a whole. Astronomy is another name for the study of the universe. Scientists use telescopes and other tools to gather information about the universe. They also study information collected during space exploration .

The Milky Way and Other Galaxies

The Milky Way Galaxy alone contains more than 100 billion stars. Some galaxies are larger, and some are much smaller. But even small galaxies contain hundreds of millions of stars. Galaxies have a variety of shapes. For example, some galaxies have the shape of a pinwheel.

The Expanding Universe

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Introduction to the universe.

The Solar System is a collection of planets, moons, asteroids and comets and other rocky objects orbiting the Sun. The Solar System is believed to extend out to at least 150 000 million km from the Sun, although the planets are all found within about 6000 million km.

Our Solar System is thought to have formed 4.6 x 10 9 years ago from a vast, rotating cloud of gas and dust known as the solar nebula. As the solar nebula rotated, its gravity began to attract gas and dust towards the centre, eventually forming our Sun.

The Sun is the powerhouse of the Solar System. Without it, life on Earth simply would not exist. Despite burning its hydrogen fuel for the best part of 5 billion years, the Sun is still only half way through its life cycle.

The study of the Sun, its environment and how the material it discharges interacts with other worlds in the Solar System is of great interest to us all. ESA has a number of mission that analyse various aspects of this solar emission.

Solar Mission

Planets and Moons

The formation of the Sun had a dramatic effect on the temperatures across the solar nebula, introducing a temperature range that stretched from about 2000K near the Sun to less than 50K at the outer regions. The heat in the inner Solar System only allowed materials with high condensation temperatures to remain solid. These particles eventually gathered to form the four terrestrial planets: Mercury, Venus, Earth and Mars.

A similar process formed the outer planets of the Solar System: Jupiter, Saturn, Uranus, and Neptune. Yet, they are different because icy materials such as frozen water, carbon dioxide and methane were also available. Consequently, these outer Jovian planets are much larger than the terrestrial planets. In addition these giant planets were able to enhance their atmospheres by capturing gas atoms moving more slowly due to the colder temperatures.

Each planet travels around the Sun in an elliptical orbit that is held in place by the gravitational attraction between the Sun and the planet. Some of the planets, including, of course, Earth, have moons orbiting them. Mars has just two moons in orbit around it, while Jupiter has 63 moons known to be orbiting it. Kepler's three laws of planetary motion define the motion of the planets around the Sun, and the movement of moons around their parent planet.

Table 1.1: Distance and Orbital Parameters for the Planets

Table 1.2: Observational Characteristics of the Planets

Asteroids and Comets

There was some material left over from the solar nebula once the Sun and the planets had formed. Some of this debris remains in our Solar System in the form of asteroids and comets.

Asteroids, which are sometimes called minor planets, are rocky bodies mostly found in the planetary region between Mars and Jupiter. This region is known as the asteroid belt, and it stretches from about 250 million km to about 600 million km from the Sun. The largest known asteroid is Ceres with a diameter of roughly 1000 km. Only around a dozen are more than 250 km across. Over 100 000 asteroids larger than one kilometre in diameter are known to exist, with more being discovered all the time.

We often hear of asteroids on the news, when near-Earth asteroids pass close enough to our planet to cause concern of a potential impact either now, or in the future. These near-Earth objects have highly elliptical orbits, which bring them into the inner Solar System, crossing the orbit of Mars and occasionally coming close to Earth.

Comets are often referred to as 'dirty snowballs', as they are made up of ice and dust. The ones we can see travel around the Sun in highly elliptical orbits taking from a few years to thousands of years to return to the inner Solar System. Typically comets are just a few kilometres across, which makes them very difficult to spot for most of their orbit. As they approach the Sun, however, solar radiation vaporizes the gases in the comet and the characteristic comet 'tail' is formed. The tail of a comet consists of two parts: a whiter part made of dust, which always points away from the Sun, and a blue part consisting of ionised gas. Comets are mainly found in two regions of the Solar System: the Kuiper belt, a region that extends from around the orbit of Pluto to about 500 AU from the Sun, and the Oort Cloud (from the Kuiper Belt to about 50 000 AU from the Sun).

Occasionally small rocks or dust particles enter the Earth's atmosphere. The dust particles and small rocks burn up in the atmosphere leaving behind brief trails in the sky witnessed as meteors. It is estimated that more than 200 million kg of meteoritic material is swept up by the Earth each year, with around 10% reaching the ground.

Much of this material orbits the Sun in distinct streams, usually as debris from different comets. At various times throughout the year the Earth crosses these streams and for a few nights an observers can witness a meteor shower.

Table 1.3: Dates of Primary Meteor Showers

Sometimes larger fragments survive their passage through the atmosphere and impact the surface, where they become known as meteorites. Most impacting fragments are tiny and cause little or no damage. Historically, however, there have been several major impacts, which may be responsible for changes in climate and the mass extinction of species.

Figure 1.1: Barringer Meteor Crater (credit: NASA)

Bodies of the Universe

It is hard to comprehend the enormity of our Universe. Our Sun is only one of billions of stars in our galaxy, known as the Milky Way. But beyond the Milky Way, there are billions of other galaxies, too. Collectively, all these galaxies, along with the vast amount of space found in between them, are called the Universe.

Extragalactic

Other Components

Dark Energy

Stellar Clusters & Constellations

We are familiar with the constellations that we see regularly in the night sky - a distinctive pattern of stars. However, although these stars may form shapes that are recognisable to us here on Earth, they do not usually have any real link to each other, as they are often at different distances from the Earth, and are in fact very far away from each other.

Figure 1.2:  View of Orion and Actual Distance to Stars

Stellar clusters, on the other hand, are systems of stars that are held together by the gravity of their members. Eventually these clusters slowly evaporate. After a few billion years, the relatively loose collections of stars known as open clusters will no longer be held together by gravity and the cluster will stop existing. More highly compacted stellar clusters, known as globular clusters, which are typically about 15 billion years old, have not yet evaporated. Due to their relatively well-known distances, and the similarities that tend to exist among their stars, stellar clusters play an important role in astrophysics. Some of the nearest stellar clusters are visible with the naked eye. The most visible open clusters are the Pleiades and Hyades, both to be found in the constellation of Taurus.

Table 1.4: List of the brightest Open and Globular Clusters

Relative Distances To Objects

A light year is the distance light travels through empty space in the course of one year.

1 light year = 9.461 x 10 12 km = 5.878 x 10 12 miles

In order to comprehend the enormity of space, astronomers use a variety of methods to measure the distances between stars and between galaxies.

Our own galaxy, the Milky Way, is around 120 000 light years across and the Sun occupies a position roughly 28 000 light years from the centre. Within the Milky Way, the nearest star to the Sun is Proxima Centauri, which is about 4.4 light years away. But most of our nearest stars are between 100 and 1000 light years away from Earth.

From any given location on Earth it is possible to view around 7000 stars with the naked eye and countless more with a telescope. In all, our galaxy contains over 1 billion stars.

The distance to stars in our galaxy is obtained using a technique called parallax. By identifying certain stellar properties it is then possible to calibrate a distance scale out to our galactic neighbours.

The nearest galactic objects are the Magellanic Clouds. The Large Magellanic Cloud is 170 000 light years away, while the Small Magellanic Cloud is at a distance of 210 000 light years. The next nearest galaxy is Andromeda (M31 in the Messier catalogue), at a distance of 2.3 million light years.

Galaxies are usually part of a larger group of galaxies. The group of galaxies that includes the Milky Way and Andromeda, plus several other smaller companion galaxies, is known as the Local Group. The other galaxies in the Local Group are between 80 000 to three million light years away from the Milky Way.

The next nearest rich cluster of galaxies, the Virgo cluster, is around 60 million light years away. It is believed that the Milky Way-Andromeda cluster is part of an even bigger supercluster along with Virgo-Coma cluster.

Stellar Motions

Diurnal effects.

During the course of one night, the constellations appear to move across the sky. Stars rise above the eastern horizon and set below the western horizon. The stars appear to rotate around one point in the sky. This optical effect occurs because the Earth itself is rotating about axis.

View the sky changing over 24 hours

Annual Effects

If you observe the night sky regularly over the course of one year, you will notice that the constellations appear to change their position slightly from one night to the next at any given time, only returning to their original positions once a year. This is due to the difference between a calendar day (24 hours) and a sidereal day (23 hours 56 minutes), or the time the Earth actually takes to spin once on its axis.

View the sky changing over 1 year

Annual Parallax

Annual Parallax is the difference between the position of a star observed from the Earth and by a hypothetical observer at the Sun. The effect is a tiny shift in the positions of relatively close stars against the background of distant stars. If the position of a nearby star is plotted during the course of a year it sweeps out an ellipse, called the parallactic ellipse, across the sky. This change in position is very small and requires high precision instruments to make the observation.

This effect, which can be observed for example with a spinning top, is caused by the gravitational pull from the Sun and Moon on the Earth's equatorial bulge. (Note - if the Earth were a perfect sphere precession would not occur.)

Precession causes the Earth's rotation axis to sweep out a circle on the sky with an angular radius of 23° 27' (this value corresponds to the axial tilt of the Earth). The circle is traced out at the rate of 1° every 71.6 years, taking 25 800 years to complete a full circle.

This means that the celestial pole, which currently points at the star Polaris, changes with time. Careful examination of the 'View of the sky changing over 24 hours' animation (above) shows the Pole Star also leaving a star trail since it is ¾ of a degree away from the celestial pole.

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3.1: Introduction to the Universe

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Learning Objectives

This chapter has several goals and objectives:

• Understand the scientific ideas of how the universe formed and is expanding
• Compare and contrast the difference and similarities between dark matter and dark energy
• Describe star systems and the various types of galaxies
• Explain the phenomenal power within stars
• Classifying and measuring distant stars

• Dynamic Earth: Introduction to Physical Geography. Authored by : R. Adam Dastrup. Located at : http://www.opengeography.org/physical-geography.html . Project : Open Geography Education. License : CC BY-SA: Attribution-ShareAlike
• M51: Cosmic Whirlpool. Provided by : NASA and European Space Agency. Located at : http://apod.nasa.gov/apod/ap050428.html . License : Public Domain: No Known Copyright

Origins of the universe, explained

The most popular theory of our universe's origin centers on a cosmic cataclysm unmatched in all of history—the big bang.

The best-supported theory of our universe's origin centers on an event known as the big bang. This theory was born of the observation that other galaxies are moving away from our own at great speed in all directions, as if they had all been propelled by an ancient explosive force.

A Belgian priest named Georges Lemaître first suggested the big bang theory in the 1920s, when he theorized that the universe began from a single primordial atom. The idea received major boosts from Edwin Hubble's observations that galaxies are speeding away from us in all directions, as well as from the 1960s discovery of cosmic microwave radiation—interpreted as echoes of the big bang—by Arno Penzias and Robert Wilson.

Further work has helped clarify the big bang's tempo. Here’s the theory: In the first 10^-43 seconds of its existence, the universe was very compact, less than a million billion billionth the size of a single atom. It's thought that at such an incomprehensibly dense, energetic state, the four fundamental forces—gravity, electromagnetism, and the strong and weak nuclear forces—were forged into a single force, but our current theories haven't yet figured out how a single, unified force would work. To pull this off, we'd need to know how gravity works on the subatomic scale, but we currently don't.

It's also thought that the extremely close quarters allowed the universe's very first particles to mix, mingle, and settle into roughly the same temperature. Then, in an unimaginably small fraction of a second, all that matter and energy expanded outward more or less evenly, with tiny variations provided by fluctuations on the quantum scale. That model of breakneck expansion, called inflation, may explain why the universe has such an even temperature and distribution of matter.

After inflation, the universe continued to expand but at a much slower rate. It's still unclear what exactly powered inflation.

Aftermath of cosmic inflation

As time passed and matter cooled, more diverse kinds of particles began to form, and they eventually condensed into the stars and galaxies of our present universe.

By the time the universe was a billionth of a second old, the universe had cooled down enough for the four fundamental forces to separate from one another. The universe's fundamental particles also formed. It was still so hot, though, that these particles hadn't yet assembled into many of the subatomic particles we have today, such as the proton. As the universe kept expanding, this piping-hot primordial soup—called the quark-gluon plasma—continued to cool. Some particle colliders, such as CERN's Large Hadron Collider , are powerful enough to re-create the quark-gluon plasma.

Radiation in the early universe was so intense that colliding photons could form pairs of particles made of matter and antimatter, which is like regular matter in every way except with the opposite electrical charge. It's thought that the early universe contained equal amounts of matter and antimatter. But as the universe cooled, photons no longer packed enough punch to make matter-antimatter pairs. So like an extreme game of musical chairs, many particles of matter and antimatter paired off and annihilated one another.

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Somehow, some excess matter survived—and it's now the stuff that people, planets, and galaxies are made of. Our existence is a clear sign that the laws of nature treat matter and antimatter slightly differently. Researchers have experimentally observed this rule imbalance, called CP violation , in action. Physicists are still trying to figure out exactly how matter won out in the early universe.

Building atoms

Within the universe's first second, it was cool enough for the remaining matter to coalesce into protons and neutrons, the familiar particles that make up atoms' nuclei. And after the first three minutes, the protons and neutrons had assembled into hydrogen and helium nuclei. By mass, hydrogen was 75 percent of the early universe's matter, and helium was 25 percent. The abundance of helium is a key prediction of big bang theory, and it's been confirmed by scientific observations.

Despite having atomic nuclei, the young universe was still too hot for electrons to settle in around them to form stable atoms. The universe's matter remained an electrically charged fog that was so dense, light had a hard time bouncing its way through. It would take another 380,000 years or so for the universe to cool down enough for neutral atoms to form—a pivotal moment called recombination. The cooler universe made it transparent for the first time, which let the photons rattling around within it finally zip through unimpeded.

We still see this primordial afterglow today as cosmic microwave background radiation , which is found throughout the universe. The radiation is similar to that used to transmit TV signals via antennae. But it is the oldest radiation known and may hold many secrets about the universe's earliest moments.

From the first stars to today

There wasn't a single star in the universe until about 180 million years after the big bang. It took that long for gravity to gather clouds of hydrogen and forge them into stars. Many physicists think that vast clouds of dark matter , a still-unknown material that outweighs visible matter by more than five to one, provided a gravitational scaffold for the first galaxies and stars.

Once the universe's first stars ignited , the light they unleashed packed enough punch to once again strip electrons from neutral atoms, a key chapter of the universe called reionization. In February 2018, an Australian team announced that they may have detected signs of this “cosmic dawn.” By 400 million years after the big bang , the first galaxies were born. In the billions of years since, stars, galaxies, and clusters of galaxies have formed and re-formed—eventually yielding our home galaxy, the Milky Way, and our cosmic home, the solar system.

Even now the universe is expanding , and to astronomers' surprise, the pace of expansion is accelerating. It's thought that this acceleration is driven by a force that repels gravity called dark energy . We still don't know what dark energy is, but it’s thought that it makes up 68 percent of the universe's total matter and energy. Dark matter makes up another 27 percent. In essence, all the matter you've ever seen—from your first love to the stars overhead—makes up less than five percent of the universe.

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The Universe

Introduction to the universe, learning objectives.

This chapter has several goals and objectives:

• Understand the scientific ideas of how the universe formed and is expanding
• Compare and contrast the difference and similarities between dark matter and dark energy
• Describe star systems and the various types of galaxies
• Explain the phenomenal power within stars
• Classifying and measuring distant stars

• Dynamic Earth: Introduction to Physical Geography. Authored by : R. Adam Dastrup. Located at : http://www.opengeography.org/physical-geography.html . Project : Open Geography Education. License : CC BY-SA: Attribution-ShareAlike
• M51: Cosmic Whirlpool. Provided by : NASA and European Space Agency. Located at : http://apod.nasa.gov/apod/ap050428.html . License : Public Domain: No Known Copyright

What is Space?

Space, the final frontier, what is it?

• Invisible radiation

Dark matter and energy

Black holes, stars, planets, asteroids and comets, galaxies and quasars.

We often refer to our expanding universe with one simple word: space. But where does space begin and, more importantly, what is it?

Space is an almost perfect vacuum, nearly void of matter and with extremely low pressure. In space, sound doesn't carry because there aren't molecules close enough together to transmit sound between them. Not quite empty, bits of gas, dust and other matter floats around "emptier" areas of the universe, while more crowded regions can host planets, stars and galaxies.

From our Earth -bound perspective, outer space is most often thought to begin about 62 miles (100 kilometers) above sea level at what is known as the Kármán line . This is an imaginary boundary at an altitude where there is no appreciable air to breathe or scatter light. Passing this altitude, blue starts to give way to black because oxygen molecules are not in enough abundance to make the sky blue.

Related: Where DOES Space Begin? Virgin Galactic Flies Right into the Debate

No one knows exactly how big space is. It's difficult to determine because of what we can see in our detectors. We measure long distances in space in "light-years," representing the distance it takes for light to travel in a year (roughly 5.8 trillion miles (9.3 trillion kilometers)). 

From the light that is visible in our telescopes, we have charted galaxies reaching almost as far back as the Big Bang, which is thought to have started our universe about 13.8 billion years ago. This means we can "see" into space at a distance of almost 13.8 billion light-years. But the universe continues to expand, making "measuring space," even more challenging. 

Additionally, astronomers are not totally sure if our universe is the only one that exists . This means that space could be a whole lot bigger than we even think.

Space radiation invisible to human eyes

The majority of space is relatively empty, with just stray bits of dust and gas floating around. This means that when humans send a probe to a distant planet or asteroid, the craft will not encounter "drag" in the same way that an airplane does as it sails through space.

In fact, the vacuum environment in space and on the moon, is one reason why the lunar lander of the Apollo program was designed to have an almost spider-like appearance , as it was described by the Apollo 9 crew. Because the spacecraft was designed to work in a zone with no atmosphere, it didn't need to have smooth edges or an aerodynamic shape.

In addition to the bits of debris that speckle the "emptier" regions of space, research has shown that these areas are also home to different forms of radiation. In our own solar system, the solar wind — charged particles that stream from the sun — emanate throughout the solar system and occasionally cause auroras near Earth's poles. Cosmic rays also fly through our neighborhood, stemming from supernovas outside of the solar system.

In fact, the universe as a whole is inundated with what is known as the cosmic microwave background (CMB), which is essentially the leftover radiation from the explosion mostly commonly known as the Big Bang. The CMB is the oldest radiation that our instruments can detect. 

Infographic: Cosmic Microwave Background Explained

There remain two giant mysteries about space: dark matter and dark energy . 

While scientists have provided extensive evidence for the existence of dark matter and dark energy, they are each still poorly understood as, so far, scientists cannot directly observe them and can only observe their effects. 

Roughly 80% of all of the mass in the universe is made up of what scientists have dubbed "dark matter," but it's not known what it actually is or if it is even matter by our current definition. However, while dark matter doesn't emit light or energy and cannot, therefore, be directly observed, scientists have found overwhelming evidence that it makes up the vast majority of the matter in the cosmos.

Dark energy might have a similar name to dark matter, but it's a whole different component entirely. 

Thought to make up nearly 75% of the universe, dark energy is a mysterious and unknown force or entity that scientists think is responsible for the universe's ongoing expansion.

Smaller black holes can form from the gravitational collapse of a gigantic star, which forms a singularity from which nothing can escape — not even light, hence the name of the object. No one is quite sure what lies within a black hole, or what would happen to a person or object who fell into it – but research is ongoing.

An example is gravitational waves, or ripples in space-time that come from interactions between black holes. This was first predicted by Albert Einstein at the turn of the last century, when he showed that time and space are linked; time speeds up or slows down when space is distorted.

As of mid-2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration has announced three black-hole interactions and mergers detected through gravitational waves, in just two years.

The team found these three events in about two years, indicating that when LIGO is implemented at full sensitivity, the observatory may be able to find these sorts of events frequently, scientists said in May 2017. Should a bunch of these black hole events be detected, it could help scientists learn how black holes of a certain size (several tens of sun masses) are born, and later merge into new black holes.

Stars (like our own sun) are immense balls of gas that produce their own radiation. They can range from red supergiants to cooling white dwarfs that are the leftovers of supernovas, or star explosions that occur when a big one runs out of gas to burn. These explosions spread elements throughout the universe and are the reason that elements such as iron exist. Star explosions can also give rise to incredibly dense objects called neutron stars . If these neutron stars send out pulses of radiation, they are called pulsar stars.

Planets are objects whose definition came under scrutiny in 2006, when astronomers were debating whether Pluto could be considered a planet or not . At the time, the International Astronomical Union (the governing body on Earth for these decisions) ruled that a planet is a celestial body that orbits the sun, is massive enough to have a nearly round shape, and has cleared its orbit of debris. Under this designation, Pluto and similar small objects are considered "dwarf planets," although not everyone agrees with the designation. After the New Horizons spacecraft flew by Pluto in 2015, principal investigator Alan Stern and others again opened up the debate, saying the diversity of terrain on Pluto makes it more like a planet.

The definition of extrasolar planets, or planets outside the solar system, is still not firmed up by the IAU, but essentially astronomers understand it to mean objects that behave like planets in our neighborhood. The first such planet was found in 1992 (in the constellation Pegasus ) and since that time, thousands of alien planets have been confirmed — with many more suspected. In solar systems that have planets under formation, these objects are often called "protoplanets" because they aren't quite the maturity of those planets we have in our own solar system.

Asteroids are rocks that are not quite big enough to be dwarf planets. We've even found asteroids with rings around them, such as 10199 Charilko. Their small size often leads to the conclusion that they were remnants from when the solar system was formed. Most asteroids are concentrated in a belt between the planets Mars and Jupiter, but there are also many asteroids that follow behind or ahead of planets, or can even cross in a planet's path. NASA and several other entities have asteroid-searching programs in place to scan for potentially dangerous objects in the sky and monitor their orbits closely. 

In our solar system, comets (sometimes called dirty snowballs) are objects believed to originate from a vast collection of icy bodies called the Oort Cloud. As a comet approaches the sun, the heat of our star causes ices to melt and stream away from the comet. The ancients often associated comets with destruction or some sort of immense change on Earth, but the discovery of Halley's Comet and related "periodic" or returning comets showed that they were ordinary solar system phenomena.

Among the biggest cosmic structures we can see are galaxies, which essentially are vast collections of stars. Our own galaxy is called the Milky Way , and is considered a "barred spiral" shape. There are several types of galaxies, ranging from spiral to elliptical to irregular, and they can change as they come close to other objects or as stars within them age.

Often galaxies have supermassive black holes embedded in the center of their galaxies, which are only visible through the radiation that each black hole emanates as well as through its gravitational interactions with other objects. If the black hole is particularly active, with a lot of material falling into it, it produces immense amounts of radiation. This kind of a galactic object is called a quasar (just one of several types of similar objects.)

Large groups of galaxies can form in clusters that are groups as large as hundreds or thousands of galaxies bound together gravitationally. Scientists consider these the largest structures in the universe.

This page was updated in Jan. 2022 by Space.com senior writer Chelsea Gohd.

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Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 covering diversity, education and gaming as well. She was contributing writer for Space.com for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House and Office of the Vice-President of the United States, an exclusive conversation with aspiring space tourist (and NSYNC bassist) Lance Bass, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, " Why Am I Taller ?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and a Bachelor of History from Canada's Athabasca University. Elizabeth is also a post-secondary instructor in communications and science at several institutions since 2015; her experience includes developing and teaching an astronomy course at Canada's Algonquin College (with Indigenous content as well) to more than 1,000 students since 2020. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: https://qoto.org/@howellspace

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Geography Notes

Universe: essay on our universe | geography.

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Here is an essay on ‘ Our Universe’ for class 6, 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Our Universe’ especially written for school and college students.

Essay on Our Universe

Our Universe contains 176 billion (one billion = 100 crores) constellations (group of stars) and each constellation includes hundreds of billion stars. Universe consists, constellation, in which Sun exists, is so big that from the core of constellation, light takes around 27 thousand years to reach up to sun. The solar system which is part of Milky Way galaxy is in disc-shaped spiral form.

Essay # 1. Sun:

Sun rotates round its axis from West to East. About 99.85% mass of solar system lies with sun only whereas planets constitute – 0.135%, comets – 0.01%, satellites – 0.00005%, dwarf planets – 0.000002%, shooting stars – 0.0000001% and inter planetary medium consists of 0.0000001% of the rest of mass.

Sun is not stationery and completes one rotation round its own axis in 25 days. One rotation of sun takes 25 days (of Earth) if observed from the equator while if we observe it from its poles, each rotation of sun takes 36 days. The rotation of sun was observed by Galileo first of all.

Sun is source of light, heat, energy and life on our Earth. Normally looking pale, this spherical ball of fire has 13 lakh multiples more volume than that of Earth and 3.25 lakh times more weight. Pressure of gaseous material on its centre is 200 billion multiples more than the pressure of air, Earth experiences while density of gases is 150 times more than that of water. Temperature of sun is 50 lakh degrees Kelvin (one Kelvin is equal to one degree on Celsius scale).

Hydrogen in form of Plasma turns into Helium at this temperature. This fusion gives birth to energy. The quantum of such produced energy may be imagined from the fact that fusion produced energy in one second is more than as much mankind has used on Earth till date. This fusion is continuous process on the surface of Sun.

Gravity of Sun is 28 times more than that of earth and black spots visible on sun are actually very powerful magnetic regions. Each magnetic regions of sun is more than 10 thousand times more powerful than magnetic power of Earth. Actual size of each black spot may be lakhs of square kilometers. Temperature at photosphere of sun is only 6000° Kelvin while ends of chromospheres experience it 10 thousand degree.

At corona this temperature varies from 10 lakh Kelvin to 50 lakh Kelvin. Continuous winds blow at the surface of sun at speed of 800 to 900 kilometer per second and these may prove dangerous for Earth at times. These winds have their fatal effect on Ionosphere. Solar storms disturb communication system on Earth. Many a times, power grids get destroyed or seized because of disturbance at the surface of Sun.

Optical telescope at Udaipur and Kodyekanal along with Radio telescope at Pune keep continuous watch over happenings related to Sun.

Essay # 2. Planets:

Planet is a Greek word which means, Wanderer. All the planets are spherical and are total eight in number.

We can group these planets in two, that is:­

a. Inner Planets:

Inner planets are those planets which are nearer to sun as compared to others. Secondly their relief constitution includes rocks and metals. These planets are known as terrestrial planets also. Namely these planets are; Mercury, Venus, Earth & Mars.

b. Outer Planets:

Outer planets are beyond asteroids and are constituted of gases, popularly known as Gas Giants. These are; Jupiter, Saturn, Uranus and Neptune.

The planets do not have any light of their own but these illuminate by reflecting sunlight and are visible at night. In the sequence of their distance from sun, these may be retented from initial alphabets of words in this sentence; My Very Efficient Mother Just Served Us Nuts.

i. Mercury:

This planet is not only smallest one but also lies closest to Sun. It does not have atmosphere of its own and is engulfed by blasts taking place because of Sun. Its core is made of iron and has this part larger than crust.

It is presumed that this crust reduced due to some comet accident. Mercury lies some 579 million (57crore 90 lakh) kilometer away from Sun and its average temperature varies between 420°C during day to -180°C at night.

It completes its revolution around Sun in 88 days while takes 58 days and 16 hours to complete its one rotation on its axis. Galileo founded Mercury in 1631 which has no satellite.

This is a rocky celestial body like Earth and second planet if counted serial vise from Sun. It completes its revolution round sun is 224.7 days while takes 243 long days to complete its rotation round its own axis from East to West.

All the other planets rotate around their axis from West to East. This hottest planet is second most glittering celestial body, first being the Moon. Also known as sister planet of Earth, Venus resembles to it in shape, size and gravity.

It has a number of volcanoes just like Earth and its surface has been formed because of volcanic eruptions. Its atmosphere consists of Carbon dioxide (96.5%) and Nitrogen. That is why it is called ‘Veiled planet’ also. Venus lies nearly 1082 million kilometers away from Sun.

iii. Earth:

Our mother planet’s name has not been derived from Greek or Roman language but from old English and Germanic. According to International Astronomical Union (IAU) biggest among Inner planets, Earth is only planet which has Geological activity taking place in its core.

Its atmosphere is also quite different to that of other planets as it consists of 77% Nitrogen and 21% Oxygen which gives it a name of ‘blue planet’. Earth is only planet where life exists. Situated nearly 14.96 crore kilometers away from sun.

The earth completes a rotation round its axis in 23 hours, 56 minutes and 4.09 seconds (approximately 24 hours) while to revolve around the sun, it takes 365 days 5 hours and 48 minutes. It has a satellite named Moon.

Known as the Red Planet, Mars is fourth planet of our solar system as counted from Sun. Its soil has very rich iron content and because of Ferrus content it looks red. As far its rotation on axis is concerned, it has similarity with Earth and it supports various seasons also.

Mars is a cold planet which has thin atmosphere. Its one rotation on its axis is completed in 24 hours, 37 minutes and 23 seconds while its revolution against sun takes 687 days. Having two satellites, Mars is placed around 2279 lakh kilometer away from sun.

The success of India to plant its Orbiter in orbit of Mars in its just first attempt has made it a pioneer and an exceptional one. Mars is only planet other than Earth which has ice-caps on its poles which have been named as Planum Boreum (North Pole) and Planum Australe (South Pole) or Southern Cap. The spacecraft that reached in the orbit of Mars is named 440 Newton Liquid Apogee Motor (LAM).

v. Jupiter:

First beyond the Asteroids, Jupiter is fifth planet of our solar system and is the biggest planet. This planet is one of the Gas Giants and has 1280 kilometer wide atmosphere composed of gases like Methane, Ammonia, Hydrogen and Helium.

It revolves around the sun in anti-clockwise direction and completes one revolution in 12 years. Its rotation on its axis is very fast and completes one in just 10 hours causing severely blowing winds.

These winds look like multi-coloured cloud belts. Jupiter is tilted on its axis at 3.1° and has more than 60 satellites. Most of the satellites are unknown for mankind as far information about them is concerned.

vi. Saturn:

The sixth from sun and second largest planet in solar system is Saturn. Situated some 1,431 million kilometers (More than 143 crore km) away from Sun, it is constituted of iron and nickel principally. Completing its rotation on its axis in 10 hours and 41 minutes, it makes one revolution around Sun in 29.5 years.

Its swift rotation gives rise to winds at the speed of 1800 kilometers per hour. Speed of winds on Saturn is higher than that on Jupiter but lesser than that on Neptune. There are nine rings around Saturn which from three arcs around it. These rings are made of frozen ice and rocks. It has around 62 satellites and biggest among them is Titan which is almost double the size of Moon. The atmosphere of Titan is thicker than that of Earth.

vii. Uranus:

This is seventh planet of our Solar System and third largest planet. Its size is 63 multiples bigger than earth but in weight it is only 14.5 multiples than that of Earth. Constituted of gases, Uranus has coldest atmosphere as compared to all the planets and has an average temperature of 223°C. Many layers of clouds are found on Uranus.

Higher cloud formation consists of Methane gas while lower formation consists of water. Speed of winds on this planet is 250 meters per second while it is tilted at 97.77° on its axis. Revolving round sun in anti-clockwise direction, it completes one revolution in 84 years while for completing one rotation around its axis, it takes 10 hours and 48 minutes.

viii. Neptune:

Neptune resembles to Uranus as seen in the Solar System. But it is smaller than Uranus and its surface is more condense. Presence of Methane gas makes it look green. Winds blow at speed of 2100 kilometers per hour in the atmosphere of this planet.

The planet consists of around 900 full circles and various incomplete arcs. Situated approximately 4,498 million kilometer away from Sun, it completes one rotation its axis in 16 hours and a revolution around sun in 164.8 years. Neptune has 13 satellites while Triton and Neried are two main satellites.

There are various dwarf planets in our solar system, out of which only five have been recognised.

1. Pluto (Earlier know as ninth planet, was declared dwarf in August, 2006)

4. Make make

Essay # 3. Satellites:

Satellites are of two types, manmade and natural. Satellites are actually celestial objects that revolve around some other celestial object. Natural satellites rotate on their axis also. They neither have atmosphere nor light of their own but due to reflection of sunlight, they look illuminated.

Manmade satellites are made of aluminium or plastic and are hardened with help of carbonic sheets. They travel at the speed which is 10 to 30 multiples more than that of an aircraft. Humankind has been benefitted extremely by manmade satellites in fields of telecommunications, weather forecasting, geological activities and atmospheric activities among other fields. India fired its first satellite named Arya Bhatt in 1975 and since then, we have sent more than 75 satellites into the orbit.

Moon is natural satellite of our Earth. It is around 3,84,403 kilometers away from Earth and takes 27.3 days to complete its revolution around Earth. As yet mankind has touched only this celestial body i.e. Moon on 21st July 1969. Atmosphere of Moon is so thin that it weighs only 104 kilograms and gravity is only one sixth part of the gravity of Earth.

Essay # 4. Asteroids or Planetoids:

These are too smaller than planets of Solar System but bigger than Asteroids. These celestial bodies revolve round the sun in anti-clockwise direction. These rocky bodies are numerous and most of these are concentrated between Mars and Jupiter. Five of them namely Ceres, Pallas, Vesta, Hypiea and Euphrosyne have been recognised. European Space Agency has found water vapour on Ceres on 22nd January, 2014.

Essay # 5. Comets:

The word comet is derived from Latin word ‘Stella Cometa’ which means ‘hairy star’. These celestial bodies were part of sun earlier and are made of frozen gases, ice and small rocky substances. Head of comet is 16 million kilometers in diameter and is followed by cloud of misty substance looking like a tail.

This tail is also lakhs of kilometer long. Tail is never towards sun facing side of comet and shines with rays from Sun. Comet which passed through Solar System was first seen in 1705 and it passes close to sun after every 75.5 years. English scientist Edmond Halley founded it and it was therefore named Halley’s Comet.

Comets are being traced regularly. Their total number was 5,186 in August, 2014. Halley’s Comet was seen in 1910, then in 1986 and next it shall be sighted in 2062. Nucleus of Halley’s Comet is 16 x 8 x 8 kilometers and it is the darkest object in solar system. This comet is periodical one and may be sighted at specific intervals but all the comets are not periodical.

Essay # 6. Meteors or Meteorites:

One can see a streak of star light in the sky sometimes, it gives an impression that any part of star has broken away. These are actually meteorites. Parts of meteorites that remain unburnt and reach our Earth in small parts are named as meteorites.

When these enter the atmosphere of Earth, burn out immediately and vanish in shape of ash most of times. A part of Arizona desert in U.S. is known to have come into form due to striking of some meteor. There are, however, various principles about formation of meteors. Some thinkers part them parts of planet which has vanished while others say these are parts of Sun, Earth and Moon only.

Indian Museum at Kolkata is known for preserving remains of meteors. Biggest such museum in Asia, it has 468 meteor parts. Their study has concluded that meteors are made of metals like iron, nickel, aluminium, oxygen and tin.

These get attracted towards Earth because of gravity of Earth. On April 21, 2013 a meteor shower was observed in many parts of the world in which more than 20 shooting stars were seen within an hour. This shower is known as Orionid Meteor Shower. Such wonderful sights are very common in our solar system.

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Essay on our universe: definition, stars and solar system.

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Essay  on Our Universe: Definition, Stars and Solar System!

When we look at the sky, we see different kinds of natural bodies like the sun, the stars, the moon, and so on. The natural bodies in the sky are called celestial bodies or heavenly bodies. They are part of our universe. The universe is a huge space which contains everything that exists. The celestial bodies that we see are just a small fraction of the bodies that exist in the universe. One of the reasons why we do not see more of them is that they are very, very far away.

To measure the large distances in the universe, scientists use a unit of length called the light year. A light year is the distance travelled by light in one year. Light travels 9.46 trillion km in a year (one trillion is 1 followed by 12 zeroes).

One light year represents this huge distance. Proxima Centauri, the star closest to our solar system, is 4.2 light years from us. This means that light from this star takes 4.2 years to reach us. In this article, we shall learn a bit about stars and our solar system. But before that, let us see how the universe was formed.

Scientists believe that the universe was born after a massive explosion called the ‘big bang’. A long time after the big bang, stars like our sun were formed. At that time, clouds of hot gases and particles revolved around the sun. Over time, many particles got stuck together to form large bodies. These bodies pulled in smaller objects near them by gravitational force. This made them larger still. These bodies finally became the planets.

Away from the lights of the city, you can see thousands of stars in the night sky. You can also see some planets and their moons, either with the naked eye or with the help of a telescope. These celestial bodies are different from the stars in one important way. Stars are celestial bodies that produce their own heat and light. Planets and their moons shine by reflecting the light of a star such as our sun.

All stars are huge balls of hydrogen and helium gases. In a star, hydrogen gets converted into helium. In this reaction, a large amount of energy is liberated. This is the source of the heat and light of a star. Stars vary in brightness and size. Some are medium-sized, like our sun. Some are so huge that if they were to be placed in our sun’s position, they would fill the entire solar system!

There are trillions of stars in the universe. They occur in groups called galaxies. The gravitational force between stars keeps the stars of a galaxy together. Apart from stars, a galaxy may have other celestial bodies like planets and moons. So you can say that a galaxy is a group of stars and other celestial bodies bound together by gravitational force.

The distribution of the stars in a galaxy can give it a shape such as spiral, ring or elliptical. Our sun is a part of a spiral galaxy called the Milky Way Galaxy. This galaxy is named after the Milky Way. The Milky Way is a band of stars that we can see on a clear night. These stars are a part of our galaxy. The ancient Romans called this band of stars Via Galactica, or ‘road of milk’. That is how our galaxy got its name.

Constellations :

As the earth moves round the sun, we see different stars at different times of the year. In the past, people found many uses for this. For example, they would get ready for sowing when particular stars appeared in the sky. Obviously, it was not possible for them to identify each and every star. So, they looked for groups of stars which seem to form patterns in the sky. A group of stars which seem to form a pattern is called a constellation.

Ancient stargazers made stories about the constellations and named them after the animals, heroes, etc., from these stories. So constellations got names like Cygnus (swan), Leo (lion), Taurus (bull), Cancer (crab), Perseus (a hero) and Libra (scale). You can see many of these constellations on a clear night.

The Great Bear (Ursa Major) is one of the easiest constellations to spot. You can see it between February and May. Its seven brightest stars form the shape of a dipper (a long-handled spoon used for drawing out water). Together, these stars are called the Big Dipper or Saptarshi. These and the other stars of the constellation roughly form the shape of a bear.

The two brightest stars of the Big Dipper are called ‘pointers’ because they point towards the pole star. The pole star lies at the tail of the bear of a smaller constellation called the Little Bear (Ursa Minor).

To find the north direction, ancient travellers would look for the Big Dipper and from there, locate the pole star. While all stars seem to move from the east to the west (as the earth rotates in the opposite direction), the pole star seems fixed. This is because it lies almost directly above the earth’s North Pole [Figure 13.3 (c)].

Orion (the Hunter) and Scorpius are two other prominent constellations. There are different stories linking them. According to one, the mighty hunter Orion vowed to kill all the animals of the world. Alarmed at this, the Earth Goddess sent a scorpion to kill Orion. He ran away, and continues to do so even now. This story takes into account the fact that Orion goes below the horizon when Scorpius rises. Orion rises again only when Scorpius sets.

Remember that constellations are imaginary. For our convenience we have picked a few stars that resemble a pattern and called them a constellation. On the other hand, galaxies are real things in which stars and other celestial bodies are held together by gravitational force.

The Solar System :

The sun is the brightest object in the sky. It is huge. It is about 333,000 times heavier than the earth, and you could fit more than a million earths inside it! Its great mass causes a large gravitational force. This keeps the sun, the planets, their moons and some other smaller bodies together as the sun’s family. The sun and all the bodies moving around it are together called the solar system. All the members of the solar system revolve around the sun in almost circular paths, or orbits.

After the sun, the planets are the largest bodies in our solar system. Scientists define a planet as a round body that orbits the sun and which has pulled in all objects near its orbit. Remember that planets were formed when large bodies in space pulled in smaller bodies near it. This cleared the space around a planet’s orbit.

There are eight planets in our solar system. In order of distance from the sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. You can remember this order as My Very Efficient Maid Just Served Us Noodles.

Apart from revolving around the sun, each planet rotates, or spins, about its axis. The time taken to complete a revolution around the sun is the length of a planet’s year. And the time taken to complete one rotation is the planet’s day.

The four planets closest to the sun—Mercury, Venus, Earth and Mars—are small, rocky planets. They are called terrestrial (earthlike) planets. The other four planets—Jupiter, Saturn, Uranus and Neptune—are giants in comparison.

They are made up mainly of gases. They are called gas giants or Jovian (Jupiter like) planets. All the gas giants have rings around them. Since they are very far from the sun, the gas giants are much colder than the terrestrial planets.

While stars twinkle, planets shine with a steady light. You can see some of the planets with the naked eyes or with the help of a good pair of binoculars. Just remember that as the planets move around the sun, they appear at different positions in the sky at different times of the year. And for the period they are behind the sun, they are not visible.

Mercury, the smallest planet of our solar system, revolves around the sun the fastest. But it rotates on its axis at a much slower speed than the earth. So, a day on Mercury is about 58 times longer than a day on earth.

Although Mercury is the closest to the sun, it is not the hottest planet. Its thin atmosphere cannot trap heat. So, at night, when there is no sun, the temperature can fall to as low as -180°C. You can see Mercury near the eastern horizon before sunrise at certain times of the year. And at certain other times, you can see it near the western horizon after sunset.

The thick atmosphere of Venus makes it the brightest and the hottest planet of the solar system. Its atmosphere has mainly carbon dioxide gas, which reflects a lot of sunlight. But it also traps so much heat that the average temperature on Venus is about 450°C.

Venus takes 243 days to complete one rotation, making its day the longest in the solar system. As a matter of fact, a day on Venus is longer than its year! It is easy to spot Venus because it is so bright. When it is visible in the east before sunrise, it is called a morning star. And when it is visible in the west in the evening, it is called an evening star.

The earth is not the fastest, slowest, hottest, coldest, largest or smallest planet. But it is the only planet on which life is known to exist. The planet’s distance from the sun, the composition of its atmosphere and the fact that liquid water is found on it make life possible on it.

Were it nearer the sun, the water on it would have evaporated. Were it farther away, all our oceans, rivers and lakes would have frozen. The carbon dioxide in the earth’s atmosphere plays two important roles. Plants use it to make food—which feeds, directly or indirectly, all animals. It also traps just enough heat to ensure that the nights on earth do not become freezing cold.

No other planet evokes so much interest as Mars does. This is because scientists have found evidence that liquid water once flowed through the channels visible on its surface. So it is possible that some form of life once existed on this planet. The rust-coloured soil of Mars gives it a red colour. So, it is also called the Red Planet.

When visible, Mars looks like a red sphere. During its two-year orbit, it looks the brightest when the earth is between the sun and Mars. During this time, you can see it rise in the east as the sun sets in the west.

Jupiter is the largest and the heaviest planet of our solar system. It also has the largest number of moons. The strong winds blowing on it, and on the other gas giants, create light and dark areas, giving them a striped look.

If you look through a powerful telescope, you will see a big spot on Jupiter’s surface. This spot is actually a huge storm, which has been raging on Jupiter for more than 300 years. In 1979, the Voyager 1 spacecraft discovered faint rings around Jupiter. These rings are not visible even through the most powerful earth-based telescopes. Jupiter is also visible to the naked eye. It looks like a bright spot in the sky.

You can easily recognise a picture of Saturn because of the planet’s prominent rings. These rings are actually particles of dust and ice revolving around Saturn. Apart from these particles, a large number of moons orbit this planet.

Uranus and Neptune:

Uranus and Neptune are the third and the fourth largest planets respectively. Yet, they were the last two planets to be discovered. That is because they are so far away from us. Even today, we know very little about them.

The moons of planets :

An object revolving around a celestial body is known as a satellite. All planets except Mercury and Venus have natural satellites, or moons, revolving around them. So far, we know of more than 150 planetary moons. Some of them are so small that they were discovered only when spacecraft flew past them. A few of the moons are almost as large as planets. One of Jupiter’s moons, Ganymede, is the largest of them all. It is even larger than Mercury. Of all the moons, we know the most about the earth’s moon.

The earth’s moon:

The earth’s moon is the brightest object in the night sky. It shines by reflecting sunlight. If you look at the moon through a telescope or a good pair of binoculars, you will see a number of craters on its surface. These are large depressions created when huge rocks from space hit the moon. The moon does not have water or an atmosphere. It also does not have life on it.

The moon takes 27 days and 8 hours to complete one revolution around the earth. In this time it also completes one rotation around its axis. We see different shapes of the moon as it travels around the earth.

Stand in front of a lamp in a darkened room. Hold a ball in your outstretched arm and move it around you, just as the moon moves around the earth. A friend standing some distance away from you will always see half of the ball (moon) lit by the lamp (sun). But to you (earth) the shape of the lit portion will keep on changing, like the changing shapes of the moon.

Sunlight lights up half of the moon. As the moon revolves around the earth, we see different parts of the sunlit half. The shapes of these parts are called the phases of the moon. When the entire side facing the earth is sunlit, the moon appears as a full disc. We call this the full moon or purnima. And when the side of the moon facing us gets no sunlight, we do not see the moon.

This is called the new moon or amavasya. After the new moon, the moon appears as a thin crescent. As days pass, we see larger portions of the moon till the full moon appears. After this, the size of the moon visible to us gradually decreases till we once again have the new moon. The whole cycle of one new moon to the next takes 29.5 days. So the new moon and the full moon appear about fifteen days from each other.

Dwarf planets :

A dwarf planet is a small, round body that orbits the sun. At the time of its formation, a dwarf planet could not pull in all other objects near its orbit. So it is not considered a planet. Pluto, which was previously considered a planet, is now considered a dwarf planet. Ceres and Eris are two other dwarf planets.

Asteroids :

In a belt between the orbits of Mars and Jupiter, millions of small, irregular, rocky bodies revolve around the sun. These are asteroids, and the belt is known as the asteroid belt. Asteroids are also called minor planets.

Scientists think that asteroids are pieces of material that failed to come together to form a planet when the solar system was being formed. Asteroids can measure a few metres to hundreds of kilometres in width. Some asteroids even have moons.

Meteoroids :

Asteroids were not the only pieces of rock left over from the formation of the solar system. Some others, called meteoroids, still orbit the sun. When they come very close to a planet such as the earth, gravitation pulls them in.

As they enter the earth’s atmosphere, they heat up because of friction with the air, and start burning. As these burning meteoroids fall towards the ground, we see them as streaks of light. The streak of light caused by a burning meteoroid is called a meteor or a shooting star.

Fortunately, the material of most meteoroids burns up completely before it can reach the surface of the earth. However, some large ones fail to burn up completely and strike the earth’s surface. Meteoroids that fall on a planet or a moon are called meteorites. A large meteorite can create a large crater and cause a lot of damage.

Scientists think that dinosaurs were wiped off the earth following a meteorite hit. Meteorite hits are more common on those planets and moons which have little or no atmosphere to burn off the falling rock. The craters on our moon have resulted from meteorite hits.

A comet is a small body of ice and dust that moves around the sun in an elongated orbit. As a comet approaches the sun, it heats up and leaves behind a stream of hot, glowing gases and dust particles. We see this as the ‘tail’ of the comet.

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The Origins of the Solar System Essay

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Introduction

The nebular hypothesis, origin of the molecular cloud, runaway star hypothesis, formation of the sun and planets, creation of the earth, formation of the oceans: comet/proto-planet impact theory, reference list.

The origin of the Sun and its orbiting planets has been a point of hypothesis and conjecture ever since man looked upon the stars and planets and wondered about their origins. For the ancient Greek and Roman civilization the celestial bodies they observed in the sky were thought of as Gods and Goddesses, looking down up the Earth from some form of godlike platform. Today, it is an established fact that the heavenly bodies we see in the night sky are composed of planets and stars, celestial bodies of rock, gas and varying forms of elements that were formed billions of years ago. Even though such objects have been observed for hundreds of years it is only within the last 200 that humanity has begun to understand their unique qualities. While there have been conjectures, varying hypothesis and age old established theories what must be understood is that as the science of astronomy evolves humanity begins to slowly adapt to new information, new discoveries and subsequent re-evaluations of what we knew of as fact. For example, early studies of astronomy adopted the geocentric model in that they believed that the sun, planets, moon and stars revolved around the Earth, not only that there was also the belief that the Earth was in fact flat (Copernicus, 2009: 83). It is based on this that when examining the established theories on the origins of the solar system one must do so with both an open yet skeptical mind, taking into account the given data and observations yet not clearly adhering to any one theory as being definitive proof.

Another interesting topic that should be taken note of is the origin of the Earth itself for just as there have been numerous theories as to the origin of the solar system there have been a plethora of theories which have attempted to determine the origin of the Earth itself. Our home planet is unique in that it is the only planet within our solar system that has sufficiently developed to be able to support life. While there have been varying accounts of how life came to be on Earth, with religion and science vying for attention, the fact remains that the uniqueness of our planet should not be underestimated and as such bodes a certain degree of curiosity as to the origins of the unique circumstances that enabled Earth to become what it is today. It is based on the various questions presented that this paper will explore the origins of the solar system and of Earth itself in order to attain a clear picture of where it came from and what its possible end could be.

Currently, one of the most widely accepted theories regarding the formation of the solar system is that of the nebular hypothesis which states that the solar system originated from a molecular cloud wherein through the introduction of an external force caused a gravitational collapse of the fragment resulting in the creation of A pre-solar nebula that would eventually become our solar system (Glassmeier, 2006: 1 – 5). While there has been no definitive evidence as to the exact origin of the external force that caused a section of the molecular cloud to collapse rather than dispersing it into space it is theorized that the energy from a nearby supernova produced sufficient enough force to cause the collapse and help trigger the necessary events needed to create the solar system. While few studies dispute the nebular hypothesis several do call into question the theory that a supernova caused the initial collapse. Studies such as those by Woolfson (2010) state that the energies from a supernova instead of causing a section of the molecular cloud to collapse would have actually dispersed a majority of the cloud into space thus preventing the formation of the solar system (Woolfson, 2000: 1 – 15). Furthermore, while the nebular hypothesis has been well established as a guiding concept in understanding the creation of celestial bodies little is known as to the precise origins of the molecular cloud that gave birth to the solar system itself. Several scientists such as Lognonne et al. (2007) state that origin of the Sun and its surrounding planets was a molecular cloud and go to great lengths explaining how it led to the creation of the solar system yet a lot of studies neglect to mention how the molecular cloud came to be in the first place (Lognonne et al., 2007: 1 -3)

While this paper has so far expounded on the nebular theory involving the Solar system’s origins as coming from a giant molecular cloud a rather interesting question comes to mind, “if the origin of the solar system is that of a giant molecular cloud where did the molecular cloud come from?”. Studies such as those by Sorrell (2008) explain that while our own sun is 4.5 billion years old the age of the universe itself has been estimated at roughly 13.75 billion years (estimate subject to change due to varying accounts as to the proper calculation) (Sorrell, 2008: 45 – 49). Furthermore it must be noted that our sun is not the oldest sun in the universe let alone in our galaxy and in fact can be considered in the prime of its “youth” as a main sequence star (Naylor, 2009: 432). It has been theorized by researchers such as Freire (2008) that a few billion years after the Big Bang, Super Massive stars, many times the temperature of our current sun and several times its size, were among the first stars to form within the universe (Freire, 2008: 459-460). These celestial bodies were able to grow to such great size due to less “competition” for available materials in order to coalesce into stars; it must be noted though that at this point in time planets were unable to form due to the lack of heavier elements in which a sufficient enough solid mass could coalesce into a planet (Dessart, 2010: 2113-2125).

Rather interestingly, it was actually due to the inherent instability of Super Massive stars that the universe became what it is today; this is due to the theory that as a direct result of their internal instability most of the original Super Massive stars became supernovas which actually caused the original molecular clouds in the universe to form (Dessart et al., 2010: 2120 – 2125). The original state of the universe was actually more “pure” in the sense that there was a distinct lack of heavier elements, as such the question of “where did the heavier elements come from?” comes to mind. This is actually resolved by looking at the activity of our own sun wherein through a process called stellar nucleosynthesis in which the nuclear reactions within the sun itself is able to help build the nuclei of elements that are heavier than hydrogen (Chiosi, 2010).

In relation to the explanation of the origins of the molecular cloud as coming from the debris from Super Massive stars Courtland (2010) presents a new theory that details exactly how the molecular cloud that spawned the solar system came to be. In her study which involved the examination of various meteorites she discovered that sealed within the rock were calcium-aluminum rich incisions (Al-26) that could only have been formed by stars that were at least 10 times as massive as the sun (Courtland, 2010: 8). Due to the fact that Super Massive stars usually form within clusters with Al 26 usually decaying rapidly due to the intense heat within such clusters it is hypothesized by Courtland (2010) that a run away must have been tossed out of its orbit as a direct result of either an explosion of a nearby Super Massive star or due to combined gravitational push by its sibling stars within the cluster (Courtland, 2010: 8). Due to Super Massive stars having a relatively short life cycle when the star became a supernova the dispersed molecules and elements became the molecular cloud that we know of today as being the primary basis of the nebular hypothesis.

Creation of the Sun

Since this paper has now established the various theories which attempt to explain the origins of the molecular cloud that brought about the creation of the solar it is now necessary to explain the current prevailing theory on how the planets and the creation of the sun came about. As mentioned earlier, in the section detailing the nebular theory, it was explained that as a direct result of a gravitational collapse of a section of the molecular cloud this precipitated the creation of the solar system (Boeyens, 2009: 493-499). A better explanation of this would be that as section of the nebula collapsed this produced a certain degree of angular momentum wherein the nebula actually began to spin faster as it collapsed in on itself. This spinning combined within the collapse produced a great deal of kinetic energy within the core of the molecular cloud until the result was a contraction of the center of the molecular cloud, which had now become a disc shaped object, into what is known as a proto-star, namely a star that has yet to have hydrogen fusion occur at its core (Boeyens, 2009: 493-499). Within 50 million years the internal temperature and pressure of the core itself was able to build to sufficient levels resulting in the start of hydrogen fusion marking the entry of the sun into its life as a main sequence star (Boeyens, 2009: 493-499)

Theory of Accretion

The theory of accretion is currently the most widely accepted theory proposing the creation of the planets, in it the theory indicates that the leftover material from the sun’s creation continued to spin around the sun slowly clumping together piece by piece until larger dust shaped particles were created (Ogihara et al., 2007: 522-530). Gradually these dust particles also began clumping together resulting in the creation of larger and larger objects until finally the entire solar system was composed of literally dozens of moon sized objects that crashed into each over a period of several million years (Ogihara et al., 2007: 522-530). It must be noted that the reason why such a process didn’t just create a system of bits and pieces of rock is due to the fact that these moon sized objects actually had viscous outer cores in the sense that their composition was similar to lava due to the high temperatures of the sun at the time and the process of accretion itself. As such when the objects collided what resulted was not a titanic clash that mutually shattered the objects but rather a process where both objects combined to form a larger structure or surfaces were “swapped” in the sense that certain parts of either proto-planet’s surface accreted to the colliding object (Ogihara et al., 2007: 522-530).

Originally the Earth was a proto-planet no bigger than the moon yet over several million years the process of accretion was able to slowly build up the Earth to its present shape. It must be noted though that the early outer core of the planet was fluid in that due to the intense heat present at the time metals that had accumulated on the planet’s surface slowly submerged into the inner core creating the metallic core that is present today (Robin, 2008: 4061 -4075). Within 150 million years of the planet reaching its current mass the surface sufficiently cooled resulting in the creation of a primitive crust, yet unlike today the surface of the Earth is estimated by studies as being roughly 1600 degrees Celsius with numerous volcanoes dotting the landscape releasing gases into the atmosphere which formed the initial atmosphere of the planet which was kept in place by Earth’s inherent gravity (Robin, 2008: 4061 -4075).

Most scientists agree that the presence of water on the Earth was the pivotal necessity necessary in order for life to start on the planet. When examining the process of Earth’s creation though there seems to be few indicators of water actually forming directly from the process of creation or within the Earth itself (Robin, 2008: 4061 -4075). One theory that attempts to explain this is the comet/proto-planet impact theory which states that proto-planets, planetoids and comets that were composed of ice were actually prevalent in the inner system during the later stages of the process of accretion. (Robin, 2008: 4061 -4075) As such as the Earth continued to orbit around the sun it supposedly impact millions of comets along with several icy proto-planets to create the water that can be seen in the oceans today. In fact, 4.4 billion years after the creation of the sun the Earth had actually sufficiently cooled enough to actually create clouds, rain, and the even oceans on the planets surface (Robin, 2008: 4061 -4075). This particular period marks the creation of the atmosphere that is present in the world today which is a combination of oxygen, carbon dioxide and other gases.

By the end of this paper it has become apparent that the process of creation of our solar system and even of our planet has been an accumulation of fortunate incidents that culminated in humanity evolving into its present state. When examining the theories explaining the creation of the molecular cloud, how Courtland (2010) presented the notion that the molecular cloud our present system came from originated from a rogue Super Massive star that coincidentally was shot out of its group by gravitational forces, that it was able to travel far enough to an area ideal enough for uninterrupted growth, that the creation of our planet was in the right place, at the right time with readily available water literally crashing into the planet in order to support life; a combination of all of these completely coincidental factors almost leads one to believe that the creation of humanity itself was no accident but on purpose. On the other hand there are quite literally billions upon billions of solar systems within the universe and it might actually be the case that the process that created the Earth is not so coincidental and that somewhere out there life similarly exists on thousands of planetary systems with the exact same composition as that of humanity yet far away enough that we cannot see the similarities at the present.

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‘Copernicus’ 2009, American Heritage Student Science Dictionary , p. 83, Science Reference Center.

Courtland, R 2010, ‘Runaway star may have spawned the solar system’, New Scientist , 205, 2754, p. 8, Academic Search Premier.

Chiosi, C 2010, ‘Primordial and Stellar Nucleosynthesis Chemical Evolution of Galaxies’, AIP Conference Proceedings , 1213, 1, pp. 42-63, Academic Search Premier.

Dessart, L, Livne, E, & Waldman, R 2010, ‘Shock-heating of stellar envelopes: a possible common mechanism at the origin of explosions and eruptions in massive stars’, Monthly Notices of the Royal Astronomical Society , 405, 4, pp. 2113-2131, Academic Search Premier.

Fazekas, A, (2010), Hubble telescope catches superfast runaway star . Web.

Freire, PC 2008, ‘Super-Massive Neutron Stars’, AIP Conference Proceedings , 983, 1, pp. 459-463, Academic Search Premier.

Glassmeier, K, Boehnhardt, H, Koschny, D, Kührt, E, & Richter, I 2006, ‘The Rosetta Mission: Flying Towards the Origin of the Solar System’, Space Science Reviews , 128, 1-4, pp. 1-21, Academic Search Premier.

Lognonne, P, Des Marais, D, Raulin, F, & Fishbaugh, K 2007, ‘Epilogue: The Origins of Life in the Solar System and Future Exploration’, Space Science Reviews , 129, 1-3, pp. 301-304, Academic Search Premier.

McFadden, L, Weissman, P, & Johnson, T 2007, Encyclopedia of the Solar System , Elsevier LTD., eBook Collection. Web.

National Astronomical Observatory of Japan. (N.I.). Hd 141569a’s disk . Web.

Naylor, T 2009, ‘Are pre-main-sequence stars older than we thought?’, Monthly Notices of the Royal Astronomical Society , 399, 1, pp. 432-442, Academic Search Premier.

N.I.. (2010). The Creation of the Earth. Web.

Ogihara, M, Ida, S, & Morbidelli, A 2007, ‘Accretion of terrestrial planets from oligarchs in a turbulent disk’, ICARUS , 188, 2, pp. 522-534, Academic Search Premier.

Photo Journal. (2007). Pia09967: water’s early journey in a solar system (artist concept) . Web.

Robin M., C 2008, ‘Accretion of the Earth’, Philosophical Transactions of the Royal Society A: Mathematical, Physical & Engineering Sciences , 366, 1883, pp. 4061-4075, Academic Search Premier.

Sorrell, WH 2008, ‘The cosmic age crisis and the Hubble constant in a non-expanding universe’, Astrophysics & Space Science , 317, 1/2, pp. 45-58, Academic Search Premier.

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Home — Essay Samples — Science — Big Bang Theory — The Origin of the Universe

The Origin of The Universe

• Categories: Big Bang Theory Universe

About this sample

Words: 445 |

Published: Mar 1, 2019

Words: 445 | Page: 1 | 3 min read

Works Cited

• Alpher, R. A., Bethe, H. A., & Gamow, G. (1948). The Origin of Chemical Elements. Physical Review, 73(7), 803-804.
• Hawking, S. (1988). A Brief History of Time. Bantam.
• Hubble, E. (1929). A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae. Proceedings of the National Academy of Sciences of the United States of America, 15(3), 168–173.
• Liddle, A. R. (2003). An Introduction to Modern Cosmology. Wiley.
• Penrose, R. (1965). Gravitational collapse and space-time singularities. Physical Review Letters, 14(3), 57–59.
• Planck Collaboration, Ade, P. A. R., Aghanim, N., Armitage-Caplan, C., Arnaud, M., Ashdown, M., ... & Zonca, A. (2015). Planck 2015 results—XIII. Cosmological parameters. Astronomy & Astrophysics, 594, A13.
• Rees, M. J. (2003). Our Cosmic Habitat. Princeton University Press.
• Riess, A. G., Filippenko, A. V., Challis, P., Clocchiatti, A., Diercks, A., Garnavich, P. M., ... & Tonry, J. (1998). Observational evidence from supernovae for an accelerating universe and a cosmological constant. The Astronomical Journal, 116(3), 1009-1038.
• Silk, J. (2001). The Big Bang. W. H. Freeman.
• Weinberg, S. (1972). Gravitation and cosmology: principles and applications of the general theory of relativity. Wiley.

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Ralph Waldo Emerson left the ministry to pursue a career in writing and public speaking. Emerson became one of America's best known and best-loved 19th-century figures. More About Emerson

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How to Write an Essay Introduction | 4 Steps & Examples

Published on February 4, 2019 by Shona McCombes . Revised on July 23, 2023.

A good introduction paragraph is an essential part of any academic essay . It sets up your argument and tells the reader what to expect.

The main goals of an introduction are to:

• Catch your reader’s attention.
• Give background on your topic.
• Present your thesis statement —the central point of your essay.

This introduction example is taken from our interactive essay example on the history of Braille.

The invention of Braille was a major turning point in the history of disability. The writing system of raised dots used by visually impaired people was developed by Louis Braille in nineteenth-century France. In a society that did not value disabled people in general, blindness was particularly stigmatized, and lack of access to reading and writing was a significant barrier to social participation. The idea of tactile reading was not entirely new, but existing methods based on sighted systems were difficult to learn and use. As the first writing system designed for blind people’s needs, Braille was a groundbreaking new accessibility tool. It not only provided practical benefits, but also helped change the cultural status of blindness. This essay begins by discussing the situation of blind people in nineteenth-century Europe. It then describes the invention of Braille and the gradual process of its acceptance within blind education. Subsequently, it explores the wide-ranging effects of this invention on blind people’s social and cultural lives.

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Table of contents

Step 1: hook your reader, step 2: give background information, step 3: present your thesis statement, step 4: map your essay’s structure, step 5: check and revise, more examples of essay introductions, other interesting articles, frequently asked questions about the essay introduction.

Your first sentence sets the tone for the whole essay, so spend some time on writing an effective hook.

Avoid long, dense sentences—start with something clear, concise and catchy that will spark your reader’s curiosity.

The hook should lead the reader into your essay, giving a sense of the topic you’re writing about and why it’s interesting. Avoid overly broad claims or plain statements of fact.

Examples: Writing a good hook

Take a look at these examples of weak hooks and learn how to improve them.

• Braille was an extremely important invention.
• The invention of Braille was a major turning point in the history of disability.

The first sentence is a dry fact; the second sentence is more interesting, making a bold claim about exactly  why the topic is important.

• The internet is defined as “a global computer network providing a variety of information and communication facilities.”
• The spread of the internet has had a world-changing effect, not least on the world of education.

Avoid using a dictionary definition as your hook, especially if it’s an obvious term that everyone knows. The improved example here is still broad, but it gives us a much clearer sense of what the essay will be about.

• Mary Shelley’s  Frankenstein is a famous book from the nineteenth century.
• Mary Shelley’s Frankenstein is often read as a crude cautionary tale about the dangers of scientific advancement.

Instead of just stating a fact that the reader already knows, the improved hook here tells us about the mainstream interpretation of the book, implying that this essay will offer a different interpretation.

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Next, give your reader the context they need to understand your topic and argument. Depending on the subject of your essay, this might include:

• Historical, geographical, or social context
• An outline of the debate you’re addressing
• A summary of relevant theories or research about the topic
• Definitions of key terms

The information here should be broad but clearly focused and relevant to your argument. Don’t give too much detail—you can mention points that you will return to later, but save your evidence and interpretation for the main body of the essay.

How much space you need for background depends on your topic and the scope of your essay. In our Braille example, we take a few sentences to introduce the topic and sketch the social context that the essay will address:

Now it’s time to narrow your focus and show exactly what you want to say about the topic. This is your thesis statement —a sentence or two that sums up your overall argument.

This is the most important part of your introduction. A  good thesis isn’t just a statement of fact, but a claim that requires evidence and explanation.

The goal is to clearly convey your own position in a debate or your central point about a topic.

Particularly in longer essays, it’s helpful to end the introduction by signposting what will be covered in each part. Keep it concise and give your reader a clear sense of the direction your argument will take.

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As you research and write, your argument might change focus or direction as you learn more.

For this reason, it’s often a good idea to wait until later in the writing process before you write the introduction paragraph—it can even be the very last thing you write.

When you’ve finished writing the essay body and conclusion , you should return to the introduction and check that it matches the content of the essay.

It’s especially important to make sure your thesis statement accurately represents what you do in the essay. If your argument has gone in a different direction than planned, tweak your thesis statement to match what you actually say.

To polish your writing, you can use something like a paraphrasing tool .

You can use the checklist below to make sure your introduction does everything it’s supposed to.

Checklist: Essay introduction

My first sentence is engaging and relevant.

I have introduced the topic with necessary background information.

I have defined any important terms.

My thesis statement clearly presents my main point or argument.

Everything in the introduction is relevant to the main body of the essay.

You have a strong introduction - now make sure the rest of your essay is just as good.

• Argumentative
• Literary analysis

This introduction to an argumentative essay sets up the debate about the internet and education, and then clearly states the position the essay will argue for.

The spread of the internet has had a world-changing effect, not least on the world of education. The use of the internet in academic contexts is on the rise, and its role in learning is hotly debated. For many teachers who did not grow up with this technology, its effects seem alarming and potentially harmful. This concern, while understandable, is misguided. The negatives of internet use are outweighed by its critical benefits for students and educators—as a uniquely comprehensive and accessible information source; a means of exposure to and engagement with different perspectives; and a highly flexible learning environment.

This introduction to a short expository essay leads into the topic (the invention of the printing press) and states the main point the essay will explain (the effect of this invention on European society).

In many ways, the invention of the printing press marked the end of the Middle Ages. The medieval period in Europe is often remembered as a time of intellectual and political stagnation. Prior to the Renaissance, the average person had very limited access to books and was unlikely to be literate. The invention of the printing press in the 15th century allowed for much less restricted circulation of information in Europe, paving the way for the Reformation.

This introduction to a literary analysis essay , about Mary Shelley’s Frankenstein , starts by describing a simplistic popular view of the story, and then states how the author will give a more complex analysis of the text’s literary devices.

Mary Shelley’s Frankenstein is often read as a crude cautionary tale. Arguably the first science fiction novel, its plot can be read as a warning about the dangers of scientific advancement unrestrained by ethical considerations. In this reading, and in popular culture representations of the character as a “mad scientist”, Victor Frankenstein represents the callous, arrogant ambition of modern science. However, far from providing a stable image of the character, Shelley uses shifting narrative perspectives to gradually transform our impression of Frankenstein, portraying him in an increasingly negative light as the novel goes on. While he initially appears to be a naive but sympathetic idealist, after the creature’s narrative Frankenstein begins to resemble—even in his own telling—the thoughtlessly cruel figure the creature represents him as.

If you want to know more about AI tools , college essays , or fallacies make sure to check out some of our other articles with explanations and examples or go directly to our tools!

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Your essay introduction should include three main things, in this order:

• An opening hook to catch the reader’s attention.
• Relevant background information that the reader needs to know.
• A thesis statement that presents your main point or argument.

The length of each part depends on the length and complexity of your essay .

The “hook” is the first sentence of your essay introduction . It should lead the reader into your essay, giving a sense of why it’s interesting.

To write a good hook, avoid overly broad statements or long, dense sentences. Try to start with something clear, concise and catchy that will spark your reader’s curiosity.

A thesis statement is a sentence that sums up the central point of your paper or essay . Everything else you write should relate to this key idea.

The thesis statement is essential in any academic essay or research paper for two main reasons:

• It gives your writing direction and focus.
• It gives the reader a concise summary of your main point.

Without a clear thesis statement, an essay can end up rambling and unfocused, leaving your reader unsure of exactly what you want to say.

The structure of an essay is divided into an introduction that presents your topic and thesis statement , a body containing your in-depth analysis and arguments, and a conclusion wrapping up your ideas.

The structure of the body is flexible, but you should always spend some time thinking about how you can organize your essay to best serve your ideas.

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How to Write an Essay Introduction (with Examples)   

The introduction of an essay plays a critical role in engaging the reader and providing contextual information about the topic. It sets the stage for the rest of the essay, establishes the tone and style, and motivates the reader to continue reading. 

Table of Contents

What is an essay introduction , what to include in an essay introduction, how to create an essay structure , step-by-step process for writing an essay introduction , how to write an introduction paragraph , how to write a hook for your essay , how to include background information , how to write a thesis statement .

• Argumentative Essay Introduction Example: 
• Expository Essay Introduction Example 

Literary Analysis Essay Introduction Example

Check and revise – checklist for essay introduction , key takeaways , frequently asked questions .

An introduction is the opening section of an essay, paper, or other written work. It introduces the topic and provides background information, context, and an overview of what the reader can expect from the rest of the work. 1 The key is to be concise and to the point, providing enough information to engage the reader without delving into excessive detail. 

The essay introduction is crucial as it sets the tone for the entire piece and provides the reader with a roadmap of what to expect. Here are key elements to include in your essay introduction: 

• Hook : Start with an attention-grabbing statement or question to engage the reader. This could be a surprising fact, a relevant quote, or a compelling anecdote. 
• Background information : Provide context and background information to help the reader understand the topic. This can include historical information, definitions of key terms, or an overview of the current state of affairs related to your topic. 
• Thesis statement : Clearly state your main argument or position on the topic. Your thesis should be concise and specific, providing a clear direction for your essay. 

Before we get into how to write an essay introduction, we need to know how it is structured. The structure of an essay is crucial for organizing your thoughts and presenting them clearly and logically. It is divided as follows: 2  

• Introduction:  The introduction should grab the reader’s attention with a hook, provide context, and include a thesis statement that presents the main argument or purpose of the essay.  
• Body:  The body should consist of focused paragraphs that support your thesis statement using evidence and analysis. Each paragraph should concentrate on a single central idea or argument and provide evidence, examples, or analysis to back it up.  
• Conclusion:  The conclusion should summarize the main points and restate the thesis differently. End with a final statement that leaves a lasting impression on the reader. Avoid new information or arguments. 

Here’s a step-by-step guide on how to write an essay introduction: 

• Start with a Hook : Begin your introduction paragraph with an attention-grabbing statement, question, quote, or anecdote related to your topic. The hook should pique the reader’s interest and encourage them to continue reading. 
• Provide Background Information : This helps the reader understand the relevance and importance of the topic. 
• State Your Thesis Statement : The last sentence is the main argument or point of your essay. It should be clear, concise, and directly address the topic of your essay. 
• Preview the Main Points : This gives the reader an idea of what to expect and how you will support your thesis. 
• Keep it Concise and Clear : Avoid going into too much detail or including information not directly relevant to your topic. 
• Revise : Revise your introduction after you’ve written the rest of your essay to ensure it aligns with your final argument. 

Here’s an example of an essay introduction paragraph about the importance of education: 

Education is often viewed as a fundamental human right and a key social and economic development driver. As Nelson Mandela once famously said, “Education is the most powerful weapon which you can use to change the world.” It is the key to unlocking a wide range of opportunities and benefits for individuals, societies, and nations. In today’s constantly evolving world, education has become even more critical. It has expanded beyond traditional classroom learning to include digital and remote learning, making education more accessible and convenient. This essay will delve into the importance of education in empowering individuals to achieve their dreams, improving societies by promoting social justice and equality, and driving economic growth by developing a skilled workforce and promoting innovation. 

This introduction paragraph example includes a hook (the quote by Nelson Mandela), provides some background information on education, and states the thesis statement (the importance of education). 

This is one of the key steps in how to write an essay introduction. Crafting a compelling hook is vital because it sets the tone for your entire essay and determines whether your readers will stay interested. A good hook draws the reader in and sets the stage for the rest of your essay.  

• Avoid Dry Fact : Instead of simply stating a bland fact, try to make it engaging and relevant to your topic. For example, if you’re writing about the benefits of exercise, you could start with a startling statistic like, “Did you know that regular exercise can increase your lifespan by up to seven years?” 
• Avoid Using a Dictionary Definition : While definitions can be informative, they’re not always the most captivating way to start an essay. Instead, try to use a quote, anecdote, or provocative question to pique the reader’s interest. For instance, if you’re writing about freedom, you could begin with a quote from a famous freedom fighter or philosopher. 
• Do Not Just State a Fact That the Reader Already Knows : This ties back to the first point—your hook should surprise or intrigue the reader. For Here’s an introduction paragraph example, if you’re writing about climate change, you could start with a thought-provoking statement like, “Despite overwhelming evidence, many people still refuse to believe in the reality of climate change.” 

Including background information in the introduction section of your essay is important to provide context and establish the relevance of your topic. When writing the background information, you can follow these steps: 

• Start with a General Statement:  Begin with a general statement about the topic and gradually narrow it down to your specific focus. For example, when discussing the impact of social media, you can begin by making a broad statement about social media and its widespread use in today’s society, as follows: “Social media has become an integral part of modern life, with billions of users worldwide.” 
• Define Key Terms : Define any key terms or concepts that may be unfamiliar to your readers but are essential for understanding your argument. 
• Provide Relevant Statistics:  Use statistics or facts to highlight the significance of the issue you’re discussing. For instance, “According to a report by Statista, the number of social media users is expected to reach 4.41 billion by 2025.” 
• Discuss the Evolution:  Mention previous research or studies that have been conducted on the topic, especially those that are relevant to your argument. Mention key milestones or developments that have shaped its current impact. You can also outline some of the major effects of social media. For example, you can briefly describe how social media has evolved, including positives such as increased connectivity and issues like cyberbullying and privacy concerns. 
• Transition to Your Thesis:  Use the background information to lead into your thesis statement, which should clearly state the main argument or purpose of your essay. For example, “Given its pervasive influence, it is crucial to examine the impact of social media on mental health.” 

A thesis statement is a concise summary of the main point or claim of an essay, research paper, or other type of academic writing. It appears near the end of the introduction. Here’s how to write a thesis statement: 

• Identify the topic:  Start by identifying the topic of your essay. For example, if your essay is about the importance of exercise for overall health, your topic is “exercise.” 
• State your position:  Next, state your position or claim about the topic. This is the main argument or point you want to make. For example, if you believe that regular exercise is crucial for maintaining good health, your position could be: “Regular exercise is essential for maintaining good health.” 
• Support your position:  Provide a brief overview of the reasons or evidence that support your position. These will be the main points of your essay. For example, if you’re writing an essay about the importance of exercise, you could mention the physical health benefits, mental health benefits, and the role of exercise in disease prevention. 
• Make it specific:  Ensure your thesis statement clearly states what you will discuss in your essay. For example, instead of saying, “Exercise is good for you,” you could say, “Regular exercise, including cardiovascular and strength training, can improve overall health and reduce the risk of chronic diseases.” 

Examples of essay introduction 

Here are examples of essay introductions for different types of essays: 

Argumentative Essay Introduction Example:  

Topic: Should the voting age be lowered to 16? 

“The question of whether the voting age should be lowered to 16 has sparked nationwide debate. While some argue that 16-year-olds lack the requisite maturity and knowledge to make informed decisions, others argue that doing so would imbue young people with agency and give them a voice in shaping their future.” 

Expository Essay Introduction Example  

Topic: The benefits of regular exercise 

“In today’s fast-paced world, the importance of regular exercise cannot be overstated. From improving physical health to boosting mental well-being, the benefits of exercise are numerous and far-reaching. This essay will examine the various advantages of regular exercise and provide tips on incorporating it into your daily routine.” 

Text: “To Kill a Mockingbird” by Harper Lee 

“Harper Lee’s novel, ‘To Kill a Mockingbird,’ is a timeless classic that explores themes of racism, injustice, and morality in the American South. Through the eyes of young Scout Finch, the reader is taken on a journey that challenges societal norms and forces characters to confront their prejudices. This essay will analyze the novel’s use of symbolism, character development, and narrative structure to uncover its deeper meaning and relevance to contemporary society.” 

• Engaging and Relevant First Sentence : The opening sentence captures the reader’s attention and relates directly to the topic. 
• Background Information : Enough background information is introduced to provide context for the thesis statement. 
• Definition of Important Terms : Key terms or concepts that might be unfamiliar to the audience or are central to the argument are defined. 
• Clear Thesis Statement : The thesis statement presents the main point or argument of the essay. 
• Relevance to Main Body : Everything in the introduction directly relates to and sets up the discussion in the main body of the essay. 

Writing a strong introduction is crucial for setting the tone and context of your essay. Here are the key takeaways for how to write essay introduction: 3  

• Hook the Reader : Start with an engaging hook to grab the reader’s attention. This could be a compelling question, a surprising fact, a relevant quote, or an anecdote. 
• Provide Background : Give a brief overview of the topic, setting the context and stage for the discussion. 
• Thesis Statement : State your thesis, which is the main argument or point of your essay. It should be concise, clear, and specific. 
• Preview the Structure : Outline the main points or arguments to help the reader understand the organization of your essay. 
• Keep it Concise : Avoid including unnecessary details or information not directly related to your thesis. 
• Revise and Edit : Revise your introduction to ensure clarity, coherence, and relevance. Check for grammar and spelling errors. 
• Seek Feedback : Get feedback from peers or instructors to improve your introduction further. 

The purpose of an essay introduction is to give an overview of the topic, context, and main ideas of the essay. It is meant to engage the reader, establish the tone for the rest of the essay, and introduce the thesis statement or central argument.  

An essay introduction typically ranges from 5-10% of the total word count. For example, in a 1,000-word essay, the introduction would be roughly 50-100 words. However, the length can vary depending on the complexity of the topic and the overall length of the essay.

An essay introduction is critical in engaging the reader and providing contextual information about the topic. To ensure its effectiveness, consider incorporating these key elements: a compelling hook, background information, a clear thesis statement, an outline of the essay’s scope, a smooth transition to the body, and optional signposting sentences.  

The process of writing an essay introduction is not necessarily straightforward, but there are several strategies that can be employed to achieve this end. When experiencing difficulty initiating the process, consider the following techniques: begin with an anecdote, a quotation, an image, a question, or a startling fact to pique the reader’s interest. It may also be helpful to consider the five W’s of journalism: who, what, when, where, why, and how.   For instance, an anecdotal opening could be structured as follows: “As I ascended the stage, momentarily blinded by the intense lights, I could sense the weight of a hundred eyes upon me, anticipating my next move. The topic of discussion was climate change, a subject I was passionate about, and it was my first public speaking event. Little did I know , that pivotal moment would not only alter my perspective but also chart my life’s course.” 

Crafting a compelling thesis statement for your introduction paragraph is crucial to grab your reader’s attention. To achieve this, avoid using overused phrases such as “In this paper, I will write about” or “I will focus on” as they lack originality. Instead, strive to engage your reader by substantiating your stance or proposition with a “so what” clause. While writing your thesis statement, aim to be precise, succinct, and clear in conveying your main argument.  

To create an effective essay introduction, ensure it is clear, engaging, relevant, and contains a concise thesis statement. It should transition smoothly into the essay and be long enough to cover necessary points but not become overwhelming. Seek feedback from peers or instructors to assess its effectiveness. 

References  

• Cui, L. (2022). Unit 6 Essay Introduction.  Building Academic Writing Skills . 
• West, H., Malcolm, G., Keywood, S., & Hill, J. (2019). Writing a successful essay.  Journal of Geography in Higher Education ,  43 (4), 609-617. 
• Beavers, M. E., Thoune, D. L., & McBeth, M. (2023). Bibliographic Essay: Reading, Researching, Teaching, and Writing with Hooks: A Queer Literacy Sponsorship. College English, 85(3), 230-242. 

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Sat / act prep online guides and tips, how to write an introduction paragraph in 3 steps.

General Education

It’s the roadmap to your essay, it’s the forecast for your argument, it’s...your introduction paragraph, and writing one can feel pretty intimidating. The introduction paragraph is a part of just about every kind of academic writing , from persuasive essays to research papers. But that doesn’t mean writing one is easy!

If trying to write an intro paragraph makes you feel like a Muggle trying to do magic, trust us: you aren’t alone. But there are some tips and tricks that can make the process easier—and that’s where we come in.

In this article, we’re going to explain how to write a captivating intro paragraph by covering the following info:  

• A discussion of what an introduction paragraph is and its purpose in an essay
• An overview of the most effective introduction paragraph format, with explanations of the three main parts of an intro paragraph
• An analysis of real intro paragraph examples, with a discussion of what works and what doesn’t
• A list of four top tips on how to write an introduction paragraph

Are you ready? Let’s begin!

What Is an Introduction Paragraph? 

An introduction paragraph is the first paragraph of an essay , paper, or other type of academic writing. Argumentative essays , book reports, research papers, and even personal  essays are common types of writing that require an introduction paragraph. Whether you’re writing a research paper for a science course or an argumentative essay for English class , you’re going to have to write an intro paragraph. 

So what’s the purpose of an intro paragraph? As a reader’s first impression of your essay, the intro paragraph should introduce the topic of your paper. 

Your introduction will also state any claims, questions, or issues that your paper will focus on. This is commonly known as your paper’s thesis . This condenses the overall point of your paper into one or two short sentences that your reader can come back and reference later.

But intro paragraphs need to do a bit more than just introduce your topic. An intro paragraph is also supposed to grab your reader’s attention. The intro paragraph is your chance to provide just enough info and intrigue to make your reader say, “Hey, this topic sounds interesting. I think I’ll keep reading this essay!” That can help your essay stand out from the crowd.

In most cases, an intro paragraph will be relatively short. A good intro will be clear, brief, purposeful, and focused. While there are some exceptions to this rule, it’s common for intro paragraphs to consist of three to five sentences . 

Effectively introducing your essay’s topic, purpose, and getting your reader invested in your essay sounds like a lot to ask from one little paragraph, huh? In the next section, we’ll demystify the intro paragraph format by breaking it down into its core parts . When you learn how to approach each part of an intro, writing one won’t seem so scary!

Once you figure out the three parts of an intro paragraph, writing one will be a piece of cake!

The 3 Main Parts of an Intro Paragraph

In general, an intro paragraph is going to have three main parts: a hook, context, and a thesis statement . Each of these pieces of the intro plays a key role in acquainting the reader with the topic and purpose of your essay. 

Below, we’ll explain how to start an introduction paragraph by writing an effective hook, providing context, and crafting a thesis statement. When you put these elements together, you’ll have an intro paragraph that does a great job of making a great first impression on your audience!

Intro Paragraph Part 1: The Hook

When it comes to how to start an introduction paragraph, o ne of the most common approaches is to start with something called a hook. 

What does hook mean here, though? Think of it this way: it’s like when you start a new Netflix series: you look up a few hours (and a few episodes) later and you say, “Whoa. I guess I must be hooked on this show!” 

That’s how the hook is supposed to work in an intro paragrap h: it should get your reader interested enough that they don’t want to press the proverbial “pause” button while they’re reading it . In other words, a hook is designed to grab your reader’s attention and keep them reading your essay! 

This means that the hook comes first in the intro paragraph format—it’ll be the opening sentence of your intro. 

It’s important to realize  that there are many different ways to write a good hook. But generally speaking, hooks must include these two things: what your topic is, and the angle you’re taking on that topic in your essay. 

One approach to writing a hook that works is starting with a general, but interesting, statement on your topic. In this type of hook, you’re trying to provide a broad introduction to your topic and your angle on the topic in an engaging way . 

For example, if you’re writing an essay about the role of the government in the American healthcare system, your hook might look something like this: 

There's a growing movement to require that the federal government provide affordable, effective healthcare for all Americans. 

This hook introduces the essay topic in a broad way (government and healthcare) by presenting a general statement on the topic. But the assumption presented in the hook can also be seen as controversial, which gets readers interested in learning more about what the writer—and the essay—has to say.

In other words, the statement above fulfills the goals of a good hook: it’s intriguing and provides a general introduction to the essay topic.

Intro Paragraph Part 2: Context

Once you’ve provided an attention-grabbing hook, you’ll want to give more context about your essay topic. Context refers to additional details that reveal the specific focus of your paper. So, whereas the hook provides a general introduction to your topic, context starts helping readers understand what exactly you’re going to be writing about

You can include anywhere from one to several sentences of context in your intro, depending on your teacher’s expectations, the length of your paper, and complexity of your topic. In these context-providing sentences, you want to begin narrowing the focus of your intro. You can do this by describing a specific issue or question about your topic that you’ll address in your essay. It also helps readers start to understand why the topic you’re writing about matters and why they should read about it. 

So, what counts as context for an intro paragraph? Context can be any important details or descriptions that provide background on existing perspectives, common cultural attitudes, or a specific situation or controversy relating to your essay topic. The context you include should acquaint your reader with the issues, questions, or events that motivated you to write an essay on your topic...and that your reader should know in order to understand your thesis. 

For instance, if you’re writing an essay analyzing the consequences of sexism in Hollywood, the context you include after your hook might make reference to the #metoo and #timesup movements that have generated public support for victims of sexual harassment. 

The key takeaway here is that context establishes why you’re addressing your topic and what makes it important. It also sets you up for success on the final piece of an intro paragraph: the thesis statement.

Elle Woods' statement offers a specific point of view on the topic of murder...which means it could serve as a pretty decent thesis statement!

Intro Paragraph Part 3: The Thesis

The final key part of how to write an intro paragraph is the thesis statement. The thesis statement is the backbone of your introduction: it conveys your argument or point of view on your topic in a clear, concise, and compelling way . The thesis is usually the last sentence of your intro paragraph. 

Whether it’s making a claim, outlining key points, or stating a hypothesis, your thesis statement will tell your reader exactly what idea(s) are going to be addressed in your essay. A good thesis statement will be clear, straightforward, and highlight the overall point you’re trying to make.

Some instructors also ask students to include an essay map as part of their thesis. An essay map is a section that outlines the major topics a paper will address. So for instance, say you’re writing a paper that argues for the importance of public transport in rural communities. Your thesis and essay map might look like this: 

Having public transport in rural communities helps people improve their economic situation by giving them reliable transportation to their job, reducing the amount of money they spend on gas, and providing new and unionized work .

The underlined section is the essay map because it touches on the three big things the writer will talk about later. It literally maps out the rest of the essay!

So let’s review: Your thesis takes the idea you’ve introduced in your hook and context and wraps it up. Think of it like a television episode: the hook sets the scene by presenting a general statement and/or interesting idea that sucks you in. The context advances the plot by describing the topic in more detail and helping readers understand why the topic is important. And finally, the thesis statement provides the climax by telling the reader what you have to say about the topic. 

The thesis statement is the most important part of the intro. Without it, your reader won’t know what the purpose of your essay is! And for a piece of writing to be effective, it needs to have a clear purpose. Your thesis statement conveys that purpose , so it’s important to put careful thought into writing a clear and compelling thesis statement. 

How To Write an Introduction Paragraph: Example and Analysis

Now that we’ve provided an intro paragraph outline and have explained the three key parts of an intro paragraph, let’s take a look at an intro paragraph in action.

To show you how an intro paragraph works, we’ve included a sample introduction paragraph below, followed by an analysis of its strengths and weaknesses.

Example of Introduction Paragraph

While college students in the U.S. are struggling with how to pay for college, there is another surprising demographic that’s affected by the pressure to pay for college: families and parents. In the face of tuition price tags that total more than $100,000 (as a low estimate), families must make difficult decisions about how to save for their children’s college education. Charting a feasible path to saving for college is further complicated by the FAFSA’s estimates for an “Expected Family Contribution”—an amount of money that is rarely feasible for most American families. Due to these challenging financial circumstances and cultural pressure to give one’s children the best possible chance of success in adulthood, many families are going into serious debt to pay for their children’s college education. The U.S. government should move toward bearing more of the financial burden of college education. 

Example of Introduction Paragraph: Analysis

Before we dive into analyzing the strengths and weaknesses of this example intro paragraph, let’s establish the essay topic. The sample intro indicates that t he essay topic will focus on one specific issue: who should cover the cost of college education in the U.S., and why. Both the hook and the context help us identify the topic, while the thesis in the last sentence tells us why this topic matters to the writer—they think the U.S. Government needs to help finance college education. This is also the writer’s argument, which they’ll cover in the body of their essay. 

Now that we’ve identified the essay topic presented in the sample intro, let’s dig into some analysis. To pin down its strengths and weaknesses, we’re going to use the following three questions to guide our example of introduction paragraph analysis: 

• Does this intro provide an attention-grabbing opening sentence that conveys the essay topic? 
• Does this intro provide relevant, engaging context about the essay topic? 
• Does this intro provide a thesis statement that establishes the writer’s point of view on the topic and what specific aspects of the issue the essay will address? 

Now, let’s use the questions above to analyze the strengths and weaknesses of this sample intro paragraph. 

Does the Intro Have a Good Hook? 

First, the intro starts out with an attention-grabbing hook . The writer starts by presenting  an assumption (that the U.S. federal government bears most of the financial burden of college education), which makes the topic relatable to a wide audience of readers. Also note that the hook relates to the general topic of the essay, which is the high cost of college education. 

The hook then takes a surprising turn by presenting a counterclaim : that American families, rather than students, feel the true burden of paying for college. Some readers will have a strong emotional reaction to this provocative counterclaim, which will make them want to keep reading! As such, this intro provides an effective opening sentence that conveys the essay topic. 

Does the Intro Give Context?

T he second, third, and fourth sentences of the intro provide contextual details that reveal the specific focus of the writer’s paper . Remember: the context helps readers start to zoom in on what the paper will focus on, and what aspect of the general topic (college costs) will be discussed later on. 

The context in this intro reveals the intent and direction of the paper by explaining why the issue of families financing college is important. In other words, the context helps readers understand why this issue matters , and what aspects of this issue will be addressed in the paper.  

To provide effective context, the writer refers to issues (the exorbitant cost of college and high levels of family debt) that have received a lot of recent scholarly and media attention. These sentences of context also elaborate on the interesting perspective included in the hook: that American families are most affected by college costs.

Does the Intro Have a Thesis? 

Finally, this intro provides a thesis statement that conveys the writer’s point of view on the issue of financing college education. This writer believes that the U.S. government should do more to pay for students’ college educations. 

However, the thesis statement doesn’t give us any details about why the writer has made this claim or why this will help American families . There isn’t an essay map that helps readers understand what points the writer will make in the essay.

To revise this thesis statement so that it establishes the specific aspects of the topic that the essay will address, the writer could add the following to the beginning of the thesis statement:

The U.S. government should take on more of the financial burden of college education because other countries have shown this can improve education rates while reducing levels of familial poverty.

Check out the new section in bold. Not only does it clarify that the writer is talking about the pressure put on families, it touches on the big topics the writer will address in the paper: improving education rates and reduction of poverty. So not only do we have a clearer argumentative statement in this thesis, we also have an essay map!  

So, let’s recap our analysis. This sample intro paragraph does an effective job of providing an engaging hook and relatable, interesting context, but the thesis statement needs some work ! As you write your own intro paragraphs, you might consider using the questions above to evaluate and revise your work. Doing this will help ensure you’ve covered all of your bases and written an intro that your readers will find interesting!

4 Tips for How To Write an Introduction Paragraph

Now that we’ve gone over an example of introduction paragraph analysis, let’s talk about how to write an introduction paragraph of your own. Keep reading for four tips for writing a successful intro paragraph for any essay. 

Tip 1: Analyze Your Essay Prompt

If you’re having trouble with how to start an introduction paragraph, analyze your essay prompt! Most teachers give you some kind of assignment sheet, formal instructions, or prompt to set the expectations for an essay they’ve assigned, right? Those instructions can help guide you as you write your intro paragraph!

Because they’ll be reading and responding to your essay, you want to make sure you meet your teacher’s expectations for an intro paragraph . For instance, if they’ve provided specific instructions about how long the intro should be or where the thesis statement should be located, be sure to follow them!

The type of paper you’re writing can give you clues as to how to approach your intro as well. If you’re writing a research paper, your professor might expect you to provide a research question or state a hypothesis in your intro. If you’re writing an argumentative essay, you’ll need to make sure your intro overviews the context surrounding your argument and your thesis statement includes a clear, defensible claim. 

Using the parameters set out by your instructor and assignment sheet can put some easy-to-follow boundaries in place for things like your intro’s length, structure, and content. Following these guidelines can free you up to focus on other aspects of your intro... like coming up with an exciting hook and conveying your point of view on your topic!

Tip 2: Narrow Your Topic

You can’t write an intro paragraph without first identifying your topic. To make your intro as effective as possible, you need to define the parameters of your topic clearly—and you need to be specific. 

For example, let’s say you want to write about college football. “NCAA football” is too broad of a topic for a paper. There is a lot to talk about in terms of college football! It would be tough to write an intro paragraph that’s focused, purposeful, and engaging on this topic. In fact, if you did try to address this whole topic, you’d probably end up writing a book!

Instead, you should narrow broad topics to  identify a specific question, claim, or issue pertaining to some aspect of NCAA football for your intro to be effective. So, for instance, you could frame your topic as, “How can college professors better support NCAA football players in academics?” This focused topic pertaining to NCAA football would give you a more manageable angle to discuss in your paper.

So before you think about writing your intro, ask yourself: Is my essay topic specific, focused, and logical? Does it convey an issue or question that I can explore over the course of several pages? Once you’ve established a good topic, you’ll have the foundation you need to write an effective intro paragraph . 

Once you've figured out your topic, it's time to hit the books!

Tip 3: Do Your Research

This tip is tightly intertwined with the one above, and it’s crucial to writing a good intro: do your research! And, guess what? This tip applies to all papers—even ones that aren’t technically research papers. 

Here’s why you need to do some research: getting the lay of the land on what others have said about your topic—whether that’s scholars and researchers or the mass media— will help you narrow your topic, write an engaging hook, and provide relatable context. 

You don't want to sit down to write your intro without a solid understanding of the different perspectives on your topic. Whether those are the perspectives of experts or the general public, these points of view will help you write your intro in a way that is intriguing and compelling for your audience of readers. 

Tip 4: Write Multiple Drafts

Some say to write your intro first; others say write it last. The truth is, there isn’t a right or wrong time to write your intro—but you do need to have enough time to write multiple drafts . 

Oftentimes, your professor will ask you to write multiple drafts of your paper, which gives you a built-in way to make sure you revise your intro. Another approach you could take is to write out a rough draft of your intro before you begin writing your essay, then revise it multiple times as you draft out your paper. 

Here’s why this approach can work: as you write your paper, you’ll probably come up with new insights on your topic that you didn’t have right from the start. You can use these “light bulb” moments to reevaluate your intro and make revisions that keep it in line with your developing essay draft. 

Once you’ve written your entire essay, consider going back and revising your intro again . You can ask yourself these questions as you evaluate your intro: 

• Is my hook still relevant to the way I’ve approached the topic in my essay?
• Do I provide enough appropriate context to introduce my essay? 
• Now that my essay is written, does my thesis statement still accurately reflect the point of view that I present in my essay?

Using these questions as a guide and putting your intro through multiple revisions will help ensure that you’ve written the best intro for the final draft of your essay. Also, revising your writing is always a good thing to do—and this applies to your intro, too!

What's Next?

Your college essays also need great intro paragraphs. Here’s a guide that focuses on how to write the perfect intro for your admissions essays. 

Of course, the intro is just one part of your college essay . This article will teach you how to write a college essay that makes admissions counselors sit up and take notice.

Are you trying to write an analytical essay? Our step-by-step guide can help you knock it out of the park.

Ashley Sufflé Robinson has a Ph.D. in 19th Century English Literature. As a content writer for PrepScholar, Ashley is passionate about giving college-bound students the in-depth information they need to get into the school of their dreams.

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Astronomy 2141 - Life in the Universe

Is there life on other planets and moons in our Solar System? Are there planets around other stars? Are any of them like the Earth? Is there intelligent life elsewhere in the universe?

Astronomy 2141, Life in the Universe , is an introduction to Astrobiology for non-science majors. It is a New General Education (GEN) Physical Science course in the Natural Science category. The goals of courses in this category are for students to understand the principles, theories, and methods of modern science, the relationship between science and technology, the implications of scientific discoveries, and the potential of science and technology to address problems of the contemporary world.

Are we alone in the universe? This is one of the oldest questions of humanity.  As little as 30 years ago we know of only one planetary system, our own.  Today we know of nearly 5000 planetary systems around other stars, many completely different than your own.  The explosion of knowledge about planets around other stars has moved the question “Are we alone?” from the realm of speculation and science fiction into the forefront of astronomical research in the 21 st century, emerging as a question that can be answered scientifically. The hunt for other Earths has emerged as one of the primary research questions driving the planning for new observatories and space missions in the 21 st century.  Life in the Universe is an introduction to Astrobiology for non-science majors. The topics covered in this course lie at the intersections between Astronomy, Chemistry, Biology, and the Earth and Planetary sciences. We will learn about scientists' ongoing quest for answers to some of the most fundamental human questions: How did life originate on Earth? Is there life on other worlds? Are we alone in the universe? What is the long-term future of life in the universe?

The course covers three primary topics:

• The emergence and nature of life on the Earth
• The potential for life on other planets in our Solar System
• The search for habitable worlds and life around other stars in our Galaxy.

The course will begin with a brief introduction to modern science and astronomy and ends with a brief discussion of the long-term future of life on Earth and in the Universe in general.

Course Topics

The course will cover the following topics.

Introduction: Imagining Other Worlds

• Week 1. Introduction and overview, how we have imagined extraterrestrial life in human cultures, the scale of the cosmos. Homework 1 assigned (due start of week 2).
• Week 2. The depths of geological and cosmic time, the nature of matter, light, and energy. Miniquiz 1 (in class). Reading: OpenStax Astronomy.

Life on Earth

• Week 3. The structure of Earth’s interior and atmosphere, the geological history of the Earth. Field trip, Orton Geological Museum. Homework 2 assigned (due start of week 4). Reading: Basin and Range .
• Week 4. Atmospheric climate regulation and climate change, the definition of life, evolution by natural selection, the structure of cells and nature of cellular metabolism. Field Trip, Byrd Polar Research Center. Miniquiz 2 (in class).
• Week 5. The chemistry of life; DNA, RNA, and heredity, and extremophile organisms. Reading: Microcosmos .
• Week 6. Abiogenesis (the origin of life from non-life), and the history of life on Earth from its earliest forms to the present day, mass extinction events and planetary impacts. Quiz 1. Field trip, Museum of Biological Diversity.

Life in the Solar System

• Week 7. Overview of our Solar System, comparison of the terrestrial planets, the giant planets and their moons. Miniquiz 3 (in class). Homework 3 assigned (due start of week 8). Reading: Openstax Astronomy . Planetarium Visit.
• Week 8. The requirements for life in a planetary context, the planet Mars, and the searches for past and present-day life on Mars. Miniquiz 4 (in class). Homework 4 assigned (due start of week 9).
• Week 9. The potential for life Jupiter’s moon Europa and Saturn’s moons Enceladus and Titan.  The habitable zone of the Sun. Quiz 2.

Life in the Universe

• Week 10. The properties of the stars, the demographics of stars in the solar neighborhood, and the life cycle of stars. Homework 5 assigned (due start of week 11). Planetarium Visit.
• Week 11. Habitable Zones around stars, the discovery and characterization of exoplanetary systems. Miniquiz 5 (in class). Reading: The Planet Factory .
• Week 12. Searches for other Earths with biosignatures, the definition of intelligent life, and the Drake Equation. Homework 6 assigned (due start of week 13). Reading: Rare Earth .
• Week 13. The search for extraterrestrial intelligence (SETI), interstellar travel and colonization, and the Fermi Paradox. Miniquiz 6 (in class). Reading: Packing for Mars .
• Week 14. Convergent evolution and the possible nature of extraterrestrial life, the possible scientific and societal impacts of detecting life elsewhere, and contact protocols if we find intelligent life. Quiz 3.

Learning Objectives (GEN)

General education learning goals & outcomes.

Goals: Successful students will:

• Successful students will analyze an important topic or idea at a more advanced and in-depth level than in the Foundations component. [Note: In this context, "advanced" refers to courses that are e.g., synthetic, reply on research or cutting-edge findings, or deeply engage with the subject matter, among other possibilities.]
• Successful students will integrate approaches to the theme by making connections to out-of-classroom experiences with academic knowledge or across disciplines and/or to work they have done in previous classes and that they anticipate doing in future.
• Successful students will appreciate the time depth of the origins and evolution of natural systems, life, humanity, or human culture, and the factors that have shaped them over time.
• Successful students will understand the origins and evolution of natural systems, life, humanity, or human culture, and the factors that have shaped them over time.

Expected Learning Outcomes, Origins & Evolution Theme

Successful students will be able to:

• 1.1. Engage in critical and logical thinking about the topic or idea of the theme.
• 1.2. Engage in an advanced, in-depth, scholarly exploration of the topic or idea of the theme.
• 2.1. Identify, describe, and synthesize approaches or experiences as they apply to the theme.
• 2.2. Demonstrate a developing sense of self as a learner through reflection, self-assessment, and creative work, building on prior experiences to respond to new and challenging contexts.
• 3.1. Illustrate their knowledge of the time depth of the universe, physical systems, life on Earth, humanity, or human culture by providing examples or models.
• 3.2. Explain scientific methods used to reconstruct the history of the universe, physical systems, life on Earth, humanity, or human culture and specify their domains of validity.
• 3.3. Engage with current controversies and problems related to origins and evolution questions.
• 4.1. Describe their knowledge of how the universe, physical systems, life on Earth, humanity, or human culture have evolved over time.
• 4.2. Summarize current theories of the origins and evolution of the universe, physical systems, life on Earth, humanity, or human culture.

Learning Objectives – GE Legacy (GEL) Course

Students taking the course for the Legacy GE (GEL) will have the following goals and expected learning outcomes.

• Successful students will engage in theoretical and empirical study within the natural sciences while gaining an appreciation of the modern principles, theories, methods, and modes of inquiry used generally across the natural sciences.
• Successful students will discern the relationship between the theoretical and applied sciences while appreciating the implications of scientific discoveries and the potential impacts of science and technology.
• 1.1. Explain basic facts, principles, theories, and methods of modern natural sciences, and describe and analyze the process of scientific inquiry.
• 1.2. Identify how key events in the development of science contribute to the ongoing and changing nature of scientific knowledge and methods.
• 1.3. Employ the processes of science through exploration, discovery, and collaboration to interact directly with the natural world when feasible, using appropriate tools, models, and analysis of data.
• 2.1. Analyze the interdependence and potential impacts of scientific and technological developments.
• 2.2. Evaluate social and ethical implications of natural scientific discoveries.
• 2.3. Critically evaluate and responsibly use information from the natural sciences.

Prerequisites

The prerequisites for this course are completion of the Natural Science GE Foundation and math at the level of Math 1050. The math in this course will not go beyond simple algebra, but there will be equations and geometrical or mathematical reasoning in some lectures and assignments. The math itself will not be difficult, but the concepts will be challenging, and translating concepts into equations and back is one of the major things you will learn during the course . The GE foundation pre-requisite is waived for students taking this course to satisfy the legacy GEL requirement (formerly Astronomy 1141). However, students should be aware that the material will be presented at a higher level than foundations courses, and they should consult with their advisor and/or the course instructor to ensure that they have adequate preparation for the course.