STARS AND OUR SOLAR SYSTEM

1] Stars and constellations : On a clear moonless night, we can see thousands of stars in the sky. Some of them form beautiful patterns.The groups of stars forming such patterns are called constellations. The International Astronomical Committee has of as far recognised 88 constellations. Of these constellations, 37 belong to the northern hemispheres ky and 51 belong to the southern hemisphere sky. Ancient Indian astronomers had imagined 27 constellations (called nakshatras). Mriga (orion) , Krittika and Saptarshi (Great Bear or Ursa Major) are some examples of the nakshatras. 2] Solar system : The sun, eight planets, moons (satellites) of planets, numerous asteroids, meteoroids, dwarf planets and comets all together form the solar system. 3] Sun : The sun is a medium sized star. It is the centre of our solar system. Its surface temparature is about 6000 degree celsius. It is big enough to hold 13 lakh earths within it. Due to its gravitational force of attraction, the planets, comets and other celestian objects revolve around the sun. 4] Planets : Mercury, Venus, Earth, Mars, Jupiter, Saturn ,Uranus and Neptune are the eight planets revolving around the sun in nearly circular orbits which are well separated from each other. The time taken by a planet to go once around sun is calle the period of revolution of the planet. It depends on the distance between the planet and the sun. If the distance is more, the period of revolution is more. Every planet rotates about its axis. The time taken by a planet to complete one rotation about its axis is called its period of rotation. It is different for different planets. 5] Satellites or moons : A small heavenly body revolving around a planet is called its satellite or moon. The earth's natural satellite, the moon, is at about 384400 km from the earth. Mercury and Venus do not have moons. Mars has two satellites. Jupiter has sixty-three satellites and Saturn has more than sixty satellites. 6] Asteroids : Small remnants of heavenly bodies revolving around the sun between the orbits of Mars and Jupiter are called asteroids. 7] Many comets revolve around the sun in highly elliptical orbits. When a comet approaches the sun, the matter in the outer layer of the comet starts vaporising and forms a tail extending millions of kilometres. Halley's comet completes one revolution around the sun in about 76 yrs. It was last seen in 1986 as it approached the sun. Some comets approaches the sun only once and then move far away from the sun, never to return. 8] Meteors : Small pieces of matter, called meteoroids, move at random in the solar system. If any of these pieces approaches the earth, it is accelerated towards it due to the gravitational force of attraction. As it enters the earth' atmosphere, a large amount of heat is generated due to friction with air. Hence its temparature rises so much that it starts burning. It is called meteors. A burning meteor looks like a shooting star. Most of the meteor burn completely before reaching the earth. The meteors which reach the earth are called meteorites. 9] Artificial satellites : India, as well as some other nations, have launched many satellites into orbits around the earth. They are called artificial satellites. They have many uses such as making contact with objects in space, communication, weather forecasting, telecommunication, broadcasting radio and T.V programmes, space research, implementing education programmes and making accurate maps. 10] Indian Radio telescope : The Tata Institute of Fundamental Research (TIFR) has set up a radio telescope (GMRT : Giant Metrewave Radio Telescope) close to the Pune-Nashik Highway at Khodad near Narayangaon. It is used in space research.