Category The Universe

            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.