My Science School

            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.

 

            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.  

               Saturn is the second largest planet of the Solar System. On the basis of the distance from the Sun, this is the sixth planet. Its distance from the Sun is 1,427 million km. Its intense brightness is due to its bigger size. It keeps on revolving round the Sun and takes about 291  years to complete one revolution. It has seventeen moons revolving round it. It appears yellow in colour. It is 96 times heavier than the Earth, while its volume is 743.7 times more than that of the Earth.

               Saturn is the most peculiar of all the planets. Its peculiarity lies in the rings surrounding it. These rings are not visible to the naked eyes but can be seen very clearly with the help of telescopes. In July, 1610 when Galileo studied it with the help of his telescope, he saw some unknown materials stuck to this planet on all sides. In 1655, a scientist named Christian Huygen discovered with the help of a powerful telescope that Saturn is surrounded by a ring which does not touch its main body at any point.

               With the help of powerful telescopes, three rings are seen very clearly. In 1969 scientists discovered a fourth ring also. The four rings of Saturn are called A, B, C, and D rings. The total width of these rings is about 274,000 km. which is twice the diameter of Saturn. Scientists are of the view that these rings might have been formed by minute particles of dust and ice.

                The outermost ring A which is somewhat brighter has its outer diameter to be 274,000 km. and its inner diameter to be 2, 38,400 km. Its width is about 16,000 km. The distance between A and B rings is 4,000 km. The B ring is the brightest. Its outer diameter is 2, 30,400 km, and the inner diameter is 1, 79,200 km. Its outer part is brighter than inner part. Its width is about 25,600 km. The distance between B and C rings is about 960 km. The C ring is not bright. Its outer diameter is 1, 77,600 km and whereas the inner diameter is 1, 43,920 km. The fourth is the D ring. This is very dim and hence it is difficult to locate its boundaries.

               All these rings appear elliptical. From the earth, all these rings appear to be connected with each other. Of all the planets Saturn is the only planet which has such rings.

            The Moon is a heavenly body. Any heavenly body that revolves round a planet is called its satellite. The Moon revolves round the Earth. Therefore, it is called a satellite of the Earth.

            The Moon is the only satellite on which man has landed. On July 20, 1969, Neil Armstrong, an American astronaut, succeeded for the first time in landing on the Moon’s surface in Apollo 11 flight and unravelled many mysteries about it. In this very flight, a retro-reflector was mounted on the Moon’s surface. Laser beams sent from the Earth’s surface and reflected back by this retro-reflector enabled scientists to calculate the exact distance of the Moon from the Earth. The distance so calculated has an accuracy of less than 15 cm. The distance has been calculated to be 3, 84,400 km.

            The Moon is a solid spherical body like a football. It completes one revolution round the Earth in an elliptical path in a period of 29 days 12 hours and 43 minutes. We call this period a lunar month. Only one side of the Moon is always visible to us because the period of its rotation on its axis is approximately the same as the period of its revolution round the Earth.

           The Moon does not have its own light but shines due to the Sun-light. Ten percent of the Sun’s light falling on the Moon is reflected by its surface while the rest is absorbed by it. During noon, the surface temperature of the Moon is about 130°C, while, during the night, it is very cold. The Moon’s surface is very uneven. There are mountains, valleys and black plains on the Moon’s surface. These black portions appear as lunar spots. There are heaps of ashes on its surface caused by the fall of meteors. The diameter of the largest crater on the Moon is 232 km which is 365.7 metres deep. Studies on the samples of rocks collected from the Moon’s surface have revealed that they contain metals like aluminium, iron, magnesium etc. The lunar surface contains silicates also. The Moon does not have air and water and, therefore, there are no signs of life there.

             The average distance of the Moon from the Earth keeps on changing slightly because of the Moon’s elliptical orbit. The diameter of the Moon is approximately 3476 km. It rotates on its axis with a speed of 3430 km per hour. The Earth is about 81.3 times heavier than the Moon and 49 times larger in volume. The force of gravity on the Moon is one-sixth that of the Earth. Scientists are making constant efforts to obtain more and more information about the Moon.

 

            Billions of stars which we see in the sky every night are made up of hot gases. Even the Sun is a star. However, there are stars which are million times more shining than the Sun, but they don’t appear so because of their greater distances from the earth. The stars are of varying sizes.

            We measure the distance of stars in units of light years. A light year is the distance travelled by light (its velocity being 3 x  km or 3 hundred thousand km per second) in one year. The star nearest to the earth (other than the Sun) is Proxima Centauri. Its distance from the earth is 4.28 light years. This star is visible only in the Southern Hemisphere. The nearest star visible in the Northern Hemisphere is Sirius. Its distance from the earth is 8.8 light years. In addition to this, another neighbouring star is Alpha Centauri which is 4.37 light years away from us.

            The farthest star from the earth which is visible with our naked eye is more than eight million light years away from us. If we use powerful telescopes, we can even see stars that are 1000 times more distant than this one. Some stars are so far away from the earth that light from them takes more than 1,000 million years to reach the earth.

            Scientists have developed various kinds of optical and radio telescopes to study stars. They have gained considerable knowledge relating to the heavenly bodies with the help of these telescopes. 

            In ancient times, when people looked up at the sky in the night, they observed many bright stars arranged in a certain pattern or group. Each group is called a constellation. It means a group of stars. Studies of movements of these constellations led to the discovery that they move in space in fixed directions. The number of constellations visible during the year at different times was found to be 12. The Sun and the Moon were always seen rising and setting in the same directions in which these twelve constellations were located. These 12 constellations were called the signs of the zodiac.

            The hypothetical part of the sky through which the Sun, the Moon and other planets seem to be passing is called the zodiac. Each of the 12 constellations situated at an angle of 30°, is named as a different sign of the zodiac. In this way the 12 signs of the zodiac have come into existence. Each sign is connected with one constellation and the shape of each constellation resembles certain earthly body or substance. The names of these signs and the position of the Sun are as follows:

1. Aries: The Ram - 21 March to 19 April


2. Taurus: The Bull - 20 April to 20 May


3. Gemini: The Twins - 21 May to 21 June


4. Cancer: The Crab - 22 June to 22 July


5. Leo: The Lion - 23 July to 22 August


6. Virgo: The Virgin - 23 August to 22 September


7. Libra: The Balance - 23 September to 23 October


8. Scorpio: The Scorpion - 24 October to 21 November


9. Sagittarius: The Archer - 22 November to 21 December


10. Capricorn: The Goat - 22 December to 19 January


11. Aquarius: The Water Bearer - 20 January to 18 February


12. Pisces: The Fish - 19 February to 20 March

     

Continue reading "What is the Zodiac? "

            When we stand in the sunlight, the rays of the Sun fall on us and we can see our shadows. Exactly like this, shadows of the Earth and the Moon are also formed in the space due to the Sun rays falling on them. Since the Earth and the Moon are spherical in shape, their shadows are conical in shape. These shadows are very long. The larger the distance of a body from the Sun, the longer will be its shadow. Lunar eclipse is darkness on the Moon due to the Earth’s shadow over a portion of it.

          While making their revolutions, the Sun, the Earth, and the Moon come in a straight line and the Earth sometimes comes in between the Sun and the Moon, thus the shadow of the Earth falls on the Moon. In other words, the Sunlight does not fall on the Moon when the Earth comes in between the two. The portion over which the shadow falls becomes dark. This is called lunar eclipse. Such a situation occurs only on Purnima (full Moon) days. Therefore, the lunar eclipse takes place only on that day. If the Earth’s shadow covers the entire Moon, it is total lunar eclipse. If the shadow covers only a part of the Moon, it is partial eclipse. Generally, there are three lunar eclipses in a year, out of which one is a total lunar eclipse.

             Now the question arises: when the full Moon comes every month, why does lunar eclipse not take place every month? The reason is that the plane of the Moon’s orbit makes an angle of 5° with the plane of the Earth’s orbit. Consequently, the Moon revolves either above or below the Earth’s shadow. So, it is only twice or thrice a year that all the three - the Sun, the Moon, and the Earth - come in one straight line. Hence the lunar eclipse does not take place every month. Astronomers, using mathematical calculations, easily predict the time and duration of the lunar eclipse.