Category Astronomy

            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.

            When we look at the sky during the night, we sometime see a star falling and making a streak of light in the atmosphere as it falls. Ultimately, it disappears. It, in fact, disintegrates. Such heavenly bodies falling after disintegration are not stars – they are meteorites. They are of varying sizes.

           Whenever any one of the celestial bodies, while making revolutions, comes nearer to the earth, it is attracted towards the earth due to its force of gravitation. Attraction of the earth increases the velocity of the body and this, in turn, increases friction with the atmospheric air. Consequently, it becomes very hot. As a result of this, hot gases start coming out of it. These gases start burning and the atmosphere is lighted. The sound of friction in the air is heard over long distance. Because of heat and friction, the body disintegrates into small pieces which are scattered in the atmosphere. But some of these meteorites are so big that they are not completely destroyed in the atmosphere and some of their parts fall on the earth.

            Meteorites become visible to us only when they are in the atmosphere, at a height of 112 km from the earth. Majority of them are destroyed in the atmosphere by the time they come down to a height of 80 km. Their downward velocity ranges from 160 km to 200 km per sec. They fall down both during the day and the night, but they are not visible during the day because of the bright sunlight.

            Meteorites are, in fact, pieces of comets. Whenever the earth approaches the orbit of some comet, some pieces of it are attracted towards the earth. These pieces may be either big or small. The biggest meteorite reaching the earth weighed 37 tons.

Continue reading “What are Meteorites?”

          All bodies of the universe attract each other. This force of attraction is called the force of gravitation. It was Newton who propounded the law of gravitation. The force of gravitation between two bodies depends upon two things – their masses and the distance between them. The greater the masses of the bodies, the greater will be the force of attraction. But, with the increase distance between them, the force as a consequence decreases. As a matter of fact, if the distance between two bodies is doubled, the force of attraction will be reduced to one-fourth.

               The Moon is a satellite of the Earth. It revolves round the Earth. The mass of the Earth is about 81 times more than that of the Moon while the Moon is only a quarter of the Earth’s diameter. The gravitational pull of the Moon is only one-sixth of the Earth’s gravity. If a man can jump one metre high on the Earth, he can jump six metres high on the Moon. Similarly, if a ball is thrown up from the surface of the Moon, it will go up six times higher than it would on the Earth.

               The Moon does not have atmosphere because of its low force of gravity. As a result, air molecules cannot be attracted towards it and they fail to stay around it. The Moon’s gravitational pull affects our Earth also. Because of this pull, water in the seas is attracted upwards causing tides. 

            The shining celestial bodies with tails are called comets. They are the members of the solar system and also revolve round the sun in definite orbits. Every comet has two parts – head and tail. They are very big in size. Many of them are so big that their heads alone are many times bigger than the sun. Their tails are millions of miles long.

            Comets are made up of rocks, dust and gases. Their tails contain ammonia, methane, water vapour and ice particles. As the sun-light falls on them, they shine. Some comets are very bright and can be seen with naked eyes but others can be observed only with the help of telescopes. Scientists have been constantly studying these comets with the help of telescopes. It is estimated that on an average, nine new comets are discovered every year.

            Halley’s Comet is the biggest amongst the comets discovered so far. It comes near the earth after every 75  years and only then it becomes visible. This was seen for the first time by the famous astronomer Edmund Halley of England in 1682, and was named after him. This was subsequently observed in 1758, 1835 and 1910. Between September 1909 and July 1911, many studies were conducted about this comet with the help of powerful telescopes. It was last seen in 1986 when space probe Giotto took its close-up photographs. It is estimated that this will be again visible in the year 2061. Some comets come near the earth after few years, but there are others which take thousands of years in this process, as they take thousands of years to complete one revolution around the sun. Sometimes the comets approaching the earth are crushed to dust and then meteoric dust falls on the earth.

            It is now believed that comets are born out of the dust generated by the bursting of volcanoes from some planets or satellites. Some scientists contend that they were formed simultaneously with the solar system. But, till now the scientists are not certain about their origin.