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Category The Universe

WHAT DOES THE UNIVERSE CONTAIN?

The Universe contains quite literally everything — from you and me to the most distant stars. It is everything and anything that exists, occupying an unimaginably vast area. Distances in space are so immense that light from the furthest galaxies takes over 10 billion light years to reach Earth, even though light travels fast enough to go round the Earth several times every second. Everything that you can see in the night sky lays our Universe, from the Sun to far-off gas clouds like the Eagle Nebula (right).

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.

Picture Credit: Google

CAN WE PROVE THERE WAS A BIG BANG?

The idea of the “Big Bang” was first suggested in the 1920s by an astronomer named Edwin Hubble. He discovered that the Universe was expanding and suggested that it must have been much smaller in the past. The most convincing argument for the Big Bang lies in the presence of cosmic back-ground radiation. This is an echo of the energy released by the Big Bang, and was detected in 1965 by two astronomers. Scientists believe that the only possible source of this radiation is the dying heat of the Big Bang.

The Big Bang theory may be nice but it has to pass the judgment of observation. Nature and experiments is the final judge of the correctness of scientific ideas. Though some details of the Big Bang still need to be perfected, the general scheme of an early hot universe with a definite beginning is accepted by most astronomers today. Even so, we have to be open to the possibility that future observations could show it to be wrong. The observations given below are sometimes said to be “proof” of the Big Bang theory. Actually, the observations are consistent with the Big Bang theory, but do not provide proof. Recall from the discussion that scientific theories cannot be proven to be correct. As of now, the Big Bang theory is the only one that can explain all of these observations.

The galaxies (or galaxy clusters) are systematically moving away from us such that the farther away galaxies are moving faster away from us. As a result of General Relativity this means that space itself is expanding carrying the galaxies with it. Both the Big Bang Theory and its major competitor, the Steady State Theory, could explain it. Recall that the Steady State Theory used the perfect cosmological principle while the Big Bang uses the cosmological principle.

The cosmic microwave background radiation can be explained only by the Big Bang theory. The background radiation is the relic of an early hot universe. The Steady State theory could not explain the background radiation, and so fell into disfavor.

The amount of activity (active galaxies, quasars, collisions) was greater in the past than now. This shows that the universe does evolve (change) with time. The Steady State theory says that the universe should remain the same with time, so once again, it does not work.

The number of quasars drops off for very large redshifts (redshifts greater than about 50% of the speed of light). The Hubble-Lemaitre Law says that these are for large look-back times. This observation is taken to mean that the universe was not old enough to produce quasars at those large redshifts. The universe did have a beginning.

The observed abundance of hydrogen, helium, deuterium, lithium agrees with that predicted by the Big Bang theory. The abundances are checked from the spectra of the oldest stars and gas clouds which are made from unprocessed, primitive material. Even better observations are those made of light from very distant quasars that have passed through gas in regions of the universe where are no stars that could have contaminated the gas. The intervening intergalactic primordial gas imprints its signature on the quasar light giving us the composition of the primordial gas. All of those places have the predicted relative abundances.

Picture Credit: Google

Where is Ursa Minor?

 

 

 

Ursa Minor is the name of a group of stars in the Northern Hemisphere. The word used in astronomy for a group of stars is “constellation”.

      The stars and constellations have Latin names. Ursa Minor means The Little Bear. Its brightest star is called Polaris, and is centered over the North Pole. It is of great importance in helping sailors to find their bearing when navigating at night.

    Star maps of the sky will help you locate the constellations.

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What is a star?

A star is a body of luminous gas, like the sun. But as stars are much farther away from the earth than the sun, they appear to be only small points of twinkling light. With the naked eye it is possible to see about 2,000 stars at any one time or place but with the most powerful telescope over 1,000 million stars are visible. Although light travels at 186,000 miles a second, the light from the stars takes many years to reach the earth.

     Stars are not fixed in space, but are travelling in different directions at different speeds.  Seen from the earth, these movements appear to be so small that groups of stars, or constellations, seem to have a permanent relationship. The star patterns we see in the sky are almost the same as those seen by our ancestors hundreds, or even thousands of years ago.

    The sizes of stars vary tremendously, from less than the diameter of the sun to thousands of times its size. Most stars appear white when looked at with the naked eye, but some are bluish-white, yellow, orange and red. The varied colours are due to differences in surface temperature. The brilliant, white stars are the hottest with surface temperatures of several hundred thousand degrees. The less brilliant, orange and res stars have surface temperatures of about 2,000 degrees.

      There are exceptions, however. Te red giant, betelgeux, in the constellation (or group) of Orion, appears to be brilliant because of its size. Its diameter is 250 million miles, which is greater than the diameter of the earth’s orbit round the sun.

     Shooting stars which are sometimes seen moving across the night sky for a few seconds are really meteors. These small particles flare up as they strike the earth’s atmosphere and usually burn out.

Picture credit: google

The Universe

What is the Milky Way?

The Milky Way is a huge mass of gas and stars that can be clearly seen as a band of light across the night sky.

            The Earth and everything else in the Solar System is part of the Milky Way. It is known as our Galaxy. It is so huge that light takes nearly 100,000 years to travel from one side to another. Where stars are packed close together the Milky Way is bright, but huge clouds of gas and dust block the light from the other parts of the Galaxy. These clouds prevent astronomers from observing the whole Milky Way.

 

 

 

 

The super supernova

Sometimes a star appears in the sky quite suddenly. This happens when there are pairs of stars rotating together. These are called binaries, and there is usually one large star called a red giant, orbiting with a smaller, hotter star. The nova takes place when gas is drawn from the red giant into the smaller star, where the heat causes a massive explosion and emits huge amounts of light. A supernova takes place when a star collapses as it begins to burn out, then suddenly explodes, producing a huge amount of light energy, and leaving behind a tiny core of neutrons, which is the heaviest substance in the Universe. A pinhead-sized mass of neutrons weighs many thousands of tonnes.

 

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The Universe

 

What was the Big Bang?

The Big Bang is the most popular theory about the creation of the Universe. According to it, the whole Universe was created in a split second in one huge explosion. All matter was squeezed together into a tiny, super-hot, dense ball that was smaller than an atom. The ball gradually expanded as it cooled, then exploded, releasing energy and matter in all directions. We cannot see the Big Bang because it would have happened billions of years ago. But we can see that the Universe is growing steadily bigger. All the galaxies are speeding away from each other as the Universe expands.

 

 

 

 

 

What is the Universe made of?

The Universe is made up almost entirely of hydrogen and helium. These are the two lightest elements. All the rest of the matter in the Universe is very rare. Elements such as silicon, carbon and others are concentrated into clouds, stars and planets. The Universe is held together by four invisible forces. Gravity and electromagnetism are the two familiar forces. The other two kinds are strong and weak nuclear forces. These operate only inside the incredibly tiny nucleus of atoms, holding the tiny particles together.

 

 

 

 

 

 

 

How old is the Universe?

It is possible to calculate the approximate age of the Universe by looking at how fast distant galaxies are moving away from us. However, it is not possible for us to make this calculation accurately. Scientists have estimated that the Universe is between 13,000 and 18,000 million year old.

INTRODUCTION – THE SOLAR SYSTEM

 

 

Look at the sky on a clear night and you can see thousands of stars. The universe contains countless millions more stars which are too far away to see. Our own part of this vast universe is called the Solar System. If we could travel from one side of the Solar System to the other it would take many years.

Telescopes enable us to see faraway objects such as galaxies.

WHAT IS THE SOLAR SYSTEM?

The Solar System is made up of the Sun, nine planets, several moons (the number changes as more are discovered) and a band of rocks called the Asteroid Belt. The planets and the Asteroid Belt all travel round the Sun. we say they ‘orbit’ the Sun. They each take a certain time to round the Sun. The time is the planet’s ‘year’. As the planets orbit, they themselves spin. They all spin at different speeds. The time they take to spin round once is called a ‘day’. Many of the planets have moons. While the planets orbit the Sun, the moons orbit the planets.

All the planets are different sizes. The Sun is so big compared to the planets that only a tiny part of it fits on the page!

The planets vary greatly in size and all are a very long way from the Sun. The planets closest to the Sun have the shortest years as they do not have as far to travel. The planets with the shortest days are the ones that spin round fastest.

ORIGINS OF THE SOLAR SYSTEM

Scientists think that the Sun and planets grew out of a cloud of dust and gas about 4,600 million years ago. Part of this cloud collapsed and shrank and got very hot. This was the beginning of the Sun. The planets formed from the left-over gas and dust that circled the Sun.

Our Sun is a star. Stars form in enormous groups called ‘galaxies’. Our Sun is part of the Milky Way galaxy. Stars are so far apart that we use special units called ‘light years’ to measure distances between them. Light travels faster than anything else in the universe. But light takes about 80,000 years to cross from one side of the Milky Way to the other! We say the Milky Way measures 80,000 light years across.

 

 

 

 

 

Birth of the Solar System

These diagrams show how the Solar System probably began. The Sun formed first at the centre of the cloud. Specks of material bumped into each other and gradually built up into lumps. These grew to form the planets.

Close to the Sun, where it was hottest, rocky planets grew. They had iron at their centres. These are the ‘inner planets’. Further from the Sun, where it was cooler, giant gas planets grew. All the planets moved around the Sun.

 

 

 

 

 

 

This spiral galaxy at the top of the photo is a similar shape to our own galaxy.

THE SUN

 

The Sun keeps the planets in their orbits. Like other stars, the Sun emits radiation in the form of heat, part of which is visible as light. Energy from the Sun is essential for life on Earth.

The Sun is huge. A hollow ball the size of the Sun could hold about a million Earths! It is also very hot. The ‘surface’ of the Sun reaches about 6,000 degree Celsius. The centre of the Sun is about 13 million degrees centigrade!

The Sun is made of the gases hydrogen and helium. At its centre, hydrogen is constantly being turned into helium. This is a nuclear reaction which releases huge amounts of energy. This energy travels to the surface of the Sun and then into space as radiation.

 

 

 

 

 

 

 

 

The surface of the Sun is called the ‘photosphere’. Here there are often dark patches called ‘sunspots’. These are areas of gas that are cooler than the rest of the surface. Although we call them spots, they are many times larger than the Earth. Giant jets of gas shoot out from the Sun. They are called ‘flares’. Sometimes arches of gas loop across the surface. These are known as ‘prominences’.

 

 

 

 

 

 

 

 

 

This picture of the Sun shows a giant loop prominence.