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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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How did the universe begin—and what were its early days like?

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.

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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.

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.

A tiny, ghostly particle called a neutrino and its antimatter counterpart, an antineutrino, could shed some light on the matter, and two big experiments, called DUNE and Hyper-Kamiokande , are using these chargeless, nearly massless particles to try to solve the mystery.

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.

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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. Scientists have tried to glimpse this “cosmic dawn,” but the results have been mixed. Back in 2018, an Australian team announced detected signs of the first stars forming around 180 million years after the big bang, though other groups haven't been able to recreate their results. By 300 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 . To astronomers' surprise, the pace of expansion is accelerating . Estimates of the expansion rate vary, but data from the James Webb Space Telescope adds to a growing body of evidence that it's significantly faster than it should be.

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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Cosmic History

The Universe’s History

The origin, evolution, and nature of the universe have fascinated and confounded humankind for centuries. New ideas and major discoveries made during the 20th century transformed cosmology – the term for the way we conceptualize and study the universe – although much remains unknown. Here is the history of the universe according to cosmologists’ current theories.

Cosmic Inflation

Around 13.8 billion years ago, the universe expanded faster than the speed of light for a fraction of a second, a period called cosmic inflation. Scientists aren’t sure what came before inflation or what powered it. It’s possible that energy during this period was just part of the fabric of space-time. Cosmologists think inflation explains many aspects of the universe we observe today, like its flatness, or lack of curvature, on the largest scales. Inflation may have also magnified density differences that naturally occur on space’s smallest, quantum-level scales, which eventually helped form the universe’s large-scale structures.

Big Bang and Nucleosynthesis

When cosmic inflation stopped, the energy driving it transferred to matter and light – the big bang. One second after the big bang, the universe consisted of an extremely hot (18 billion degrees Fahrenheit or 10 billion degrees Celsius) primordial soup of light and particles. In the following minutes, an era called nucleosynthesis, protons and neutrons collided and produced the earliest elements – hydrogen, helium, and traces of lithium and beryllium. After five minutes, most of today’s helium had formed, and the universe had expanded and cooled enough that further element formation stopped. At this point, though, the universe was still too hot for the atomic nuclei of these elements to catch electrons and form complete atoms. The cosmos was opaque because a vast number of electrons created a sort of fog that scattered light.

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Recombination

Around 380,000 years after the big bang, the universe had cooled enough that atomic nuclei could capture electrons, a period astronomers call the epoch of recombination. This had two major effects on the cosmos. First, with most electrons now bound into atoms, there were no longer enough free ones to completely scatter light, and the cosmic fog cleared. The universe became transparent, and for the first time, light could freely travel over great distances. Second, the formation of these first atoms produced its own light. This glow, still detectable today, is called the cosmic microwave background. It is the oldest light we can observe in the universe.

After the cosmic microwave background, the universe again became opaque at shorter wavelengths due to the absorbing effects of all those hydrogen atoms. For the next 200 million years the universe remained dark. There were no stars to shine. The cosmos at this point consisted of a sea of hydrogen atoms, helium, and trace amounts of heavier elements.

First Stars

Gas was not uniformly distributed throughout the universe. Cooler areas of space were lumpier, with denser clouds of gas. As these clumps grew more massive, their gravity attracted additional matter. As they became denser, and more compact, the centers of these clumps became hotter – hot enough eventually that nuclear fusion occurred in their centers. These were the first stars. They were 30 to 300 times more massive than our Sun and millions of times brighter. Over several hundred million years, the first stars collected into the first galaxies.

Reionization

At first, starlight couldn’t travel far because it was scattered by the relatively dense gas surrounding the first stars. Gradually, the ultraviolet light emitted by these stars broke down, or ionized, hydrogen atoms in the gas into their constituent electrons and protons. As this reionization progressed, starlight traveled farther, breaking up more and more hydrogen atoms. By the time the universe was 1 billion years old, stars and galaxies had transformed nearly all this gas, making the universe transparent to light as we see it today.

For many years, scientists thought the universe’s current expansion was slowing down. But in fact, cosmic expansion is speeding up. In 1998, astronomers found that certain supernovae, bright stellar explosions, were fainter than expected. They concluded this could only happen if the supernovae had moved farther away, at a faster rate than predicted.

Scientists suspect a mysterious substance they call dark energy is accelerating expansion. Future research may yield new surprises, but cosmologists suggest it’s likely the universe will continue to expand forever.

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Black Holes

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

The Origin of The Universe

• Categories: Big Bang Theory Universe

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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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Essay Samples on Universe

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Best topics on Universe

1. Unraveling the Cosmos: About the Origin of the Universe

2. From Geocentric to Heliocentric: The Evolution of Astronomical Thought

3. History of Telescopes and the Revolutionary Launch of the Hubble Space Telescope

4. Analysis of the Probabilities of Earth Extinction Scenarios

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15. Hubble Space Telescope: Creation, Usage and Prospects

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Essay: The Universe

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• Subject area(s): Science essays
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• Published: 22 September 2015*
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Abstract The universe is a known place to our young and sensitive eyes. Stars galaxies, planets, comets, asteroids are part of this abundant place that has an end of 13. 8 billion years to us. The age of the universe was known by studying the oldest objects within the universe, which can be studied using binary system or the HR Diagram. Knowing how fast the universe is expanding can be done by knowing how close and far are objects from us and their velocity towards or away from our galaxy. Finally we can know the observable universe by knowing how light and light speed works and travels in space. Introduction What is in the universe? Galaxies, planets, stars, comets, asteroids, and much other chemical composition ‘stuff’ are part of the universe. We are not able to see the entire universe but just the observable part of it. The observable universe is a term referring to the volume of space that we are physically able to detect, it can be defined as what we are potentially able to see, is there more? That is unknown to our eyes. The universe is 13.8 billion years old to us this is until what our eyes can see. The age of the universe was known because of these main reasons, one, by studying the oldest objects within the universe and second, by measuring how fast the universe is expanding, but the one and most important is knowing how light and light speed works and travels in space. Main body Studying the oldest objects within the universe Many countless objects are part of the universe having each a different birthday, one year, ten years and up to a billion years of age. Studying the age of the objects in the universe has some work attached to it. The life cycle of a star is based on its mass (Redd). We can know that if a star is bright it has a bigger mass causing it to have a longer life cycle. Measuring the mass of a star is easier when using a binary system. Binary system is when two (bi) start orbit around each other. By measuring the orbital speed the orbital period and the size of the orbit we can get to know the mass of both the stars. Another easy method to know the mass of the star and therefore the age of it is using the H-R diagram. Depending where the star is in the H-R diagram we can know the mass and therefore its age. Therefore an example can be, if we want to know the age of star ‘A’ and star ‘B’ we first measure the speed, the orbital period between star ‘A’ and star ‘B’, the size of the orbit and we get to know the mass both. The stellar mass is the mass that we have been using and continue to use in order to know determine the age of a star. Hertzsprung’Russell diagram One of the most useful and powerful plots in astrophysics is the Hertzsprung-Russell diagram (hereafter called the H-R diagram). It originated in 1911 when the Danish astronomer, Ejnar Hertzsprung, plotted the absolute magnitude of stars against their colour (hence effective temperature). Independently in 1913 the American astronomer Henry Norris Russell used spectral class against absolute magnitude. Their resultant plots showed that the relationship between temperature and luminosity of a star was not random but instead appeared to fall into distinct groups (Australia). This diagram has several different representation one of which is called the observational Hertzsprung- Russell diagram or color-magnitude diagram (CMD). What this diagram does is that when stars are at the same distance it compares the color, using the color index which can state which star is more luminous. Therefore once we are able to know which star is more luminous we can determine it age. How fast the universe is expanding For a fact we know that stars die but there are some stars that live longer than other and by discovering how old is one star and them discovering that another star is older we have come to know that they may not be the limit and by looking more in to it we may find older objects. The universe is expanding every day away from us and towards us. Galaxies and stars are moving and we can know if a star is close to us, away from us or if it is moving closer or farther away from us. Knowing the wavelength range by using infrared light can answer us where are the stars standing now and once we know where the stars are know we can know their color and therefore their age. Farther stars and galaxies are moving way faster from us that does closer stars and galaxies, this is due to the young age they have which allows them to move in a faster rate. Light The speed of light is what determines our possible visibility of the universe. The speed of light is defines as C= the speed of light= 300,000km/s or 3.0 * 10^8 m/s. A light year is the distance traveled in one year. If you see a star that is 40 light years away, you are seeing it as it was 40 years ago. Thus the deeper you peek into space, the farther you are seeing back in time. Any event that happened beyond a certain point in the past is unknowable to us if the signal from it hasn’t had time to reach us (Observable universe). We can see up to objects that are 13.8 billion light years away from us because 13.8 billion light years is our visible limit. For that reason the universe that old, and there may be more but it has not yet reached our eyes. Conclusion Human beings have a limit of the visibility of the universe. The universe to our yes is enormous with all different stars ‘stuff’ that are part of it. Our eyes and our telescopes can only see back to 13.8 billion years. The light has traveled to us in a speed of 13.8 billion light years, and has not yet seen more. We do not have knowledge of how old or what is beyond what we see, this will be known in several billion years more, if they are to come.

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