Category The Universe

              The question whether there is life on planets other than the Earth has often perplexed scientists. If it is true that there is life on planets other than the Earth, what could be the possible ways of establishing contact with the living beings of other planets?

               It is felt that only radio can help to solve this problem. In 1960 American scientists received radio signals from some stars that created a hope about the existence of life on some other heavenly bodies. However, they could not get any concrete evidence to prove this.

                     A few years ago, people talked of having seen some unidentified flying objects (UFO’S) in the sky at many places. It was observed that the flying objects were shaped like saucers. People called them flying saucers. This led scientists to think of the possibility of life on other planets as well. It was felt that these saucers were extra-terrestrial attempts at scientific experiments. These saucers had different shapes. Some of them were round while others were cigar shaped. Many stories were heard about their colours. Their speed was reported to be very high.

                  These flying saucers have also been photographed. They were even chased by aeroplanes. A thorough study of these objects revealed that the so-called flying saucers were either balloons launched for weather studies or some meteoric bodies. Now scientists are of the view that the Earth is the only planet which has favourable conditions for the existence of life. Scientists have not found any other planet in the universe where there is life.

 

              The universe includes the Sun, Earth, solar system, galaxies and everything else that exists. Even with the most powerful telescopes, astronomers can not see the limit of the universe. Most scientists believe, however, the universe is mostly a vast empty space.

              Now the question that arises is how did this universe come into existence? There are many theories regarding its origin. According to one theory, the entire matter in the beginning of the universe was like a fire-ball. At a certain time, a big explosion took place and the matter of this giant fire ball got scattered in all directions. On cooling down these scattered parts gave birth to the galaxies. The matter of these galaxies has been expanding continuously.

            This incident took place around 20 billion years ago. Obviously, if this expansion continues, it will make the universe empty.

            However, according to another theory, because of the force of gravitation, a time will come when the expansion of the galaxies will stop, and they will start contracting. This suggests a pulsating universe. Again, according to a third theory, new galaxies are constantly under formation and the matter of the older galaxies goes on scattering. This is the theory of the balanced universe. It is difficult to say which of the three theories is authentic. However, in order to propound a correct theory regarding the origin of the universe and its existence, researches are still in process.

 

            When we look at the sky in the night, a dim strip of milky colour extending far and wide is seen. This is our Milky Way or ‘Akash Ganga’. With the help of the powerful telescopes, it has been observed that the Milky Way contains innumerable stars, dust and gases. Its milky colour is due to the presence of cluster of stars. The Solar System also belongs to this galaxy. There are billions of such galaxies in the universe.

            Scientists have studied the shape, size and structure of the Milky Way with the help of the powerful telescopes. It is like a lens, whose central part is very thick and edges are thin. Our Solar System is situated at the thin edge. When we look at the sky, we are, in fact, looking at the centre of the Milky Way. That is why the stars present in it seem to have clustered together. Studies have revealed that the Milky Way is spiral-shaped. It has around 150 trillion stars.

            Do you know the size of the Milky Way? Its size can not be measured in terms of kilometres. There is a separate unit for measuring large distances. This unit is called a light year, which is the distance travelled by light in a year. We know that light travels with a velocity of 30 thousand km per second. In a year, it will travel a distance of 9 million km. This distance is called one light year. The diameter of Milky Way is one hundred thousand light years. The sun is located at a distance of 30 thousand light years from the centre of the Milky Way. Our sun also revolves around this Milky Way and takes 225 million years to complete one revolution.

            If we look carefully at the Milky Way, some black parts are also seen. These are the regions which have less stars and more dust. 

We see innumerable stars in the sky every night. Some of the stars are very bright while others are dim. Some are small, others are big. You must be curious to know how stars came into existence.

All these stars, in fact, have evolved from the gases and clouds of particles spread in space. Whenever such clouds or gases due to their own gravitational pull, contract, they get transformed into a spherical ball. In order to evaluate it to convert into a star, the weight of such a cloud should be thousand times more than that of the sun. When such a cloud starts contracting, the pressure so generated produces heat. A portion of this heat is radiated out in various directions. This helps the cloud to further contract. A stage is reached when the cloud is broken into several pieces and every piece goes on contracting. When these pieces become very hot, they start radiating light and then each shining piece becomes a self-luminous star.

These stars continue their contraction further till the temperature, at their centres reaches millions of degree centigrade. At this temperature thermo-nuclear reactions start. These reactions are similar to those which take place in a hydrogen bomb. In these reactions four nucleus of hydrogen combine to form a helium nucleus. The emission of energy from the stars is caused by these reactions.

These stars exist as long as their hydrogen content does not go below ten percent. Their life span extends to billions of years. Our Sun is also a star in which thermonuclear reactions are going on. As a result of these reactions, we have been receiving heat and light energy from the Sun constantly. It is estimated that our Sun will live for 10 billion years. Half of its life is, of course, over.

 

            If you look at the sky in the night you will observe that some stars are brighter than others. On viewing through powerful telescopes, we not only observe a difference in their brightness, but also in their colours.

            The brightness and colour of the stars, in fact, depend on their temperature. The higher the temperature, the brighter is the star.

            The relationship between colour and temperature helps in determining the brightness of a star. The Stars whose colour appears to be red or orange are colder than those whose colour is yellow or green. ‘White’ stars are hotter than ‘yellow’ or ‘green’ stars, and that the ‘blue’ stars have the highest surface temperature.

            The surface temperature of ‘blue’ stars is around 27,750° C or even more. The Sun is a ‘yellow’ star and as such its temperature is much less than that of the ‘blue’ stars. Its surface temperature is nearly 6,000° C. The stars which appear to be red are colder and less bright. Their surface temperature is around 1,650° C or even less. All these facts make it clear that the brightness of stars is related to their surface temperature. Since brightness is reduced by distance, stars with very high surface temperature but at a great distance from us, look less bright than those whose surface temperature is less but are nearer to the Earth. 

          The Solar System consists of the Sun, the nine planets and their moons, asteroids comets, meteoroids and other debris. The Sun holds all these objects in fixed orbits by its strong gravitational pull. The Sun makes up 99% of the solar systems mass. Most of the solar system is a vast emply space.

          The study of the nine planets is necessary for the study of the Solar System.

Mercury: Mercury is the smallest planet of the Solar System and nearest to the Sun. It takes 88 days to complete one revolution round the Sun and the same time to complete one rotation on its own axis. It is difficult to see it very clearly because of its extreme proximity to the Sun. However, studies reveal that there are many hills on its surface. There is no water on this planet. Its distance from the Sun is 58 million kms or 36 million miles.

Venus: Venus is the planet nearest to the Earth. Its distance from the Sun is 108 million km. It is approximately of the same size and weight as is the earth. It takes 224.7 days to complete one revolution round the Sun and thirty days to complete one rotation on its own axis. It has some atmosphere. Man has already launched his spacecraft on this planet.

Earth: Earth is the only planet of the Solar System that is inhabited by living beings. Its distance from the Sun is 150 million km. It takes 365  days to complete one revolution round the Sun. To complete one rotation on its own axis, it takes about 24 hours. The Moon is a satellite of the Earth and revolves round it.

Mars: Mars is red in appearance. Besides the Earth, this is the only planet where signs of vegetation are found. Studies have revealed that it has mounts of ice on its poles. Its distance from the Sun is 228 million km. It takes about 687 days to make one revolution round the Sun. On its own axis, it makes one rotation in 24 hours and 37 minutes. It has two small moons—Phogos and Diamos.

Jupiter: Jupiter is the biggest planet of the solar family. Its distance from the Sun is 778 million km. or 484 million miles. It completes one revolution round the Sun in 11.8 years, whereas it makes one rotation on its own axis in 9 hours and 50 minutes. It is 317 times heavier than the Earth. Being at a great distance from the Sun, it is an extremely cold planet. It has altogether 14 moons.

Saturn: Saturn is a peculiar planet of the Solar System. Its distance from the Sun is 1,427 million km. It takes 29  years to complete one revolution round the Sun, but only 10 hours and 14 minutes to make one rotation on its own axis. There are many rings round it. It has 10 moons.

Uranus: Uranus completes one revolution round the Sun in 84 years. But it takes 10 hours and 49 minutes to make one rotation on its own axis. Its distance from the Sun is 2,870 km. It has five moons.

Neptune: Neptune takes 164.8 years in making one revolution round the Sun. It completes one rotation on its own axis in about 15 hours and 48 minutes. Its distance from the Sun is 4,497 million km. It has two moons.

Pluto: Pluto is the farthest planet from the Sun. It completes one revolution of the Sun in 248.4 years. On its own axis it takes 153 hours to complete one rotation. Its distance from the Sun is 5,900 million km. It has one moon.        

           In addition to these planets, there are about 1,700 asteroids which also revolve round the Sun. They lie between Mars and Jupiter. They are, in fact, small pieces broken away from the bigger planets and since have been revolving round the Sun.

 

            Sun is one of the billions of stars in the sky. It forms the nucleus of the Solar System. All planets revolve around the Sun in elliptical orbits. It looks bright and big because of its nearness to the Earth than the other stars. It is at a distance of 150 million kilometres from the earth. Its diameter is 13, 92,000 km, compared to the Earth’s diameter of 12,756 km. Its volume is approximately 1.3 million times more than that of the Earth. Even though it is gaseous, it weighs more than 300,000 times as much as the earth. It takes 8 minutes 20 seconds for its rays to reach the Earth.

           Like other heavenly bodies, the Sun also is not static. It, along with its family of nine planets, revolves round the Milky Way and takes about 225 million years to complete one revolution. It also rotates on its own axis. The temperature at its centre is approximately 15 million degree centigrade. The solar surface is composed of three gaseous layers. The inner most layers are called ‘photosphere’. Its temperature is 6000° C. The solar spots are seen on this very layer. The next layer is ‘chromospheres’ which is approximately 14,000 km thick. This is composed of hydrogen, helium and other gases. The temperature of this layer is about 5000° C. The outer layer of the Sun is called ‘corona’.

               The Sun not only gives light to the Earth, but also gives life to its inhabitants. The Sun is the biggest source of heat and energy. Without it, there is, of course, no question of life on the Earth.

 

               The most spectacular feature of the Sun’s surface is the ‘Sunspots’. Galileo was the first man to observe these spots in 1610 with the help of his telescope. Through the telescope the Sunspots looked like dark holes on the shining surface of the Sun.

               These spots often appear in groups. They increase in number, and then diminish in regular cycles. These cycles repeat every seventh, eleventh or fourteenth year. The portion of the Sun having these spots emits light of less intensity. According to modern scientific theories, these spots are formed by reactions between the electrically charged gases of the Sun and solar magnetic fields. When at any place on the Sun, strong magnetic field develops; the temperature of that place is lowered. Consequently, these portions appear as black spots amidst hotter and brighter portions. The temperature of these spots is approximately 4000° C. They are not permanent but go on changing.

               Can you imagine the size of these spots? Some spots are big enough to accommodate hundreds of earths. Even a small spot is so big that it can cover two-thousandth part of the Sun’s surface. These spots are spread over an area of 500 million square miles on the Sun. On June 4, 1946 scientists saw a Sunspot measuring 4, 80,000 km in length and 1, 12,000 km in breadth. Most of the solar spots last for a few days only. But some may last for two months or even more.

               It is inferred from the change of state of Sunspots that, like the earth, the Sun is also rotating on its own axis. These spots are moving from East to West because the Sun is moving from East to West. Changes occur in the location, sizes and rotation period of these spots. 

           We know that the Earth is a planet in the Solar System and revolves around the Sun. Similarly the Moon is a satellite of the Earth and revolves around it. The Earth and the Moon cast long shadows in space as the Sun’s light falls on them. When the Sun, the Earth and the Moon come in one straight line and the Moon comes in between the Earth and the Sun, the Moon obscures the Sun from our view. This is solar eclipse. For people living in that particular part of the earth, it becomes almost dark. The situation in which the Sun, the Moon and the Earth come in a straight line occurs only on new moon-days. The solar eclipse, therefore, takes place only on new moon-days.

            However, the solar eclipse does not take place on every new moon-day. The reason for this is that the plane of earth’s orbit makes an angle of 5° with the orbit plane of the Moon. Had their orbits been in the same plane, we would have seen solar eclipse on every new moon day. Because of this angle, the revolving moon is sometimes above and sometimes below the orbit plane of the Earth. Only sometimes they come in one straight line.

           By knowing the position of the Earth, the Sun and the Moon, solar eclipse and its duration, can be predicted in advance. If the Moon obstructs the full Sun, there is total solar eclipse and if the Moon obstructs only a part of the Sun, it will be a partial solar eclipse. In total solar eclipse, the edge of the Sun is visible.              

          Total solar eclipses are of great importance to the scientists as, during the period of eclipse, the shining edge of the Sun and other parts can be easily studied. Solar eclipse can take place twice a year or five times at the most. During 1935 there were five solar eclipses. In 1982 four solar eclipses took place. The total solar eclipse which took place on February 16, 1980 and was seen in India lasted for a very long time.