GEOGRAPHY

Know Interesting Facts about Solar System

• The Universe or the Cosmos, as perceived today, consists of millions of Galaxies. A galaxy is a huge congregation of stars held together by the forces of gravity.
• Edwin Hubble in 1924 first demonstrated existence of galaxies beyond Milky Way. He proved that these galaxies are flying away from each other and that the farther they are, the faster they fly. This means that the universe is expanding like a balloon that is being blown up.
• In 140 AD, Ptolemy propounded the theory that the earth was the centre of the universe and the sun and other heavenly bodies revolved around it. In 1543, Copernicus argued that the sun and not the earth was the centre of the universe.
• However, he still equated the universe with the solar system. Kepler supported Copernicus but said that the sun was the centre of the solar system and not the universe. In 1805, Hershel made it clear that the solar system was a part of the much larger system of stars called galaxy.
• Our galaxy is Milky Way Galaxy (or the Akash Ganga). It is spiral in shape. It consists of over a 100 billion stars rotating and revolving about its centre. Nearest galaxy to ours is Andromeda.
• The Big Bang Theory evaluates that 15 billion years ago, cosmic matter (universe) was in an extremely compressed state, from which expansion started by a primordial explosion. This explosion broke up the super dense ball and cast its fragments far out into space, where they are still traveling at thousands of miles per second. 

Measurement Units of Space are :

• Light Year : It is the distance covered by light in one year in vacuum at a speed of 3 105 km/s. Astronomical Unit (A.U) : It is the mean distance between the earth and the sun. One light year is equal to 60,000 A.U.
• Parsec : It represents the distance at which the mean radius of earth’s orbit subtends an angle of one second of an arc. It is equal to 3.26 light years.Stars are self – luminous bodies that account for 98 per cent of the material in the galaxy. The rest 2 per cent consists of interstellar or galactic gas and dust in an attenuated form.
• A star’s colour indicates the temperature of its surface. Blue colour denotes maximum temperature. Then comes yellow, then red, etc.
• The life of a star is spread over billions of years. It begins to form by compression of galactic gas and dust. Compression generates heat which in turn causes hydrogen to be converted into helium in nuclear fusion, thereby emitting large amount of heat and light.
• If the star is of sun’s size, it becomes a White Dwarf. Their central density can reach up to 10grams per cubic cm.
• If die star is bigger than the sun but not more than twice as big, it will turn into a Neutron Star or Pulsar. Their central density is 1014 grams per cubic cm. They are formed due to Novae or Super novae explosion.
• Stars having mass greater than three times that of the sun, because of their great gravitational power, have contracteso much that they have developed super density of 1016 grams per cubic cm. It is so dense that nothing, not even light, can escape from its gravity and hence called ‘Black Hole’.
• Brightest star outside our Solar System is Sirius, also called Dog Star.
• Closest star of Solar System is Proxima Centauri (4.2 light years away). Then come Alpha Centauri (4.3 light years away) and Barnard’s Star (5.9 light years away).