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Universe – The Beginning Astronomers are now fairly sure that the Universe was born 15 billion years ago due to the Big Bang. The Big Bang theory tells us how the Universe began and that it is evolving. Basically, it is a theory that was created to explain two facts that we know about the Universe - it is gradually expanding and cooling at the same time. In the 1920s, Edwin Hubble found that the galaxies far from our own Milky Way are moving away from us. So he concluded that the whole Universe must have been expanding. Working backwards, this means that at one stage, the Universe must have originated from a single point. Our Solar System To reach mercury it takes 5.5 earth months. It has the widest range in temperature of any planet, from a chilly -170°C at night to a sizzling 350°C during the day. This is because it has no atmosphere. Venus is the brightest object in the sky after the Sun and Moon. It is the hottest planet – temperatures can go up to 480 Celsius. This is because the gases in the atmospheres act as good insulators and trap all the heat of the sun – this is called the greenhouse effect! Mars is also called the ‘Red planet’(after the Roman god of war) because of its colour. It has the largest volcano(extinct) in the solar system and is named Olympus Mons. It is 27km high and 700 km wide! Scientists believe that one day they might find life on Mars. Jupiter is the largest planet in the solar system. It is a ‘gas giant’. It has the largest number of moons (about 63). The surface appears banded because of belts of clouds. It has a giant red spot(3 times the size of the Earth) – which is actually the largest storm in the solar system raging for over 300 years! Our Solar System Saturn is the next of the “gas giants’. It is the least dense planet – it could in fact float on water if there was an ocean large enough. It has a spectacular ring system made of particles and ice crystals. It took Voyager II, 29 years to reach Saturn. Neptune is the fourth gas giant. It also appears to be blue in colour – though no one knows why. It also has a system of rings. It has the wildest weather in the solar system with winds raging up to 2000 km per hour! Uranus is the third largest planet in the solar system. It is also a gas giant. It has a blue colour. This is because the atmosphere has methane gas which absorbs red light and the blue light is reflected. It also has rings – but these are not visible. It is the only planet to spin on its side. Pluto is the smallest planet. It is half the size of the moon. It is also the coldest planet (temperatures are around – 200 Degrees Celsius). It has a funny orbit and for twenty years it is closer to the sun than Neptune! When this happens Neptune is the farthest planet of the solar system. It is made up of rock and ice. Beyond the Solar System Our Solar System was a vast cloud of gas and dust billions of years ago. Comets are made of the same material, a part of cosmos at athat time. TheThe comets When a large star haswhich burnt formed all its fuel, it explodes into Supernova. stuffconsist that is of the chunks ofextremely hydrogen, ice dust which then escaped the gravitational pull ofin the Sun Nebula is the Latin word forand ‘cloud’. It is a cosmic cloudIfof gas and dust floating left becomes dense to form a ‘Neutron Star’. this Neutron Star is too as it was being leftover masses the material then startedit orbiting space. Nebulae are These the basic building blocks outcosmic of which starsdue and large, itThe exerts aformed. tremendous gravitational pulloftowards the center tosolar which round the Sunbeen These are and called Comets. A comet has comprising hydrogen cornea systems have made. Bulk of the Nebulae consists of hydrogen and that helium starts imploding further becomes even denser. It nucleus becomes so dense duewith to its and a tail of dust gas.escape Many comets beenhole discovered using powerful telescopes a small percentage of heavy metals. It is have then presence ofathese metals that give the gravity even light and cannot it. Hence a black is region in space-time from available nowadays. The most comet is the Halley’s Comet which to was nebulae different Nebulae are verycannot vast. Sometimes these extend which nothing cancolours. escape. The famous black holes be seen but its presence can last be seen in 1986. Itusing orbits round the Sun and appears once in 75 years. As such, it is expected to pass thousands of the light years in extent. known radio telescopes. the solar system in the year 2061. Halley’s Comet This picture is a Nebula Our Universe – The end If the expansion continues forever then the Universe is destined for the Big Freeze, gradually pulled apart into a cold desolate wasteland of dying stars and black holes. OR If space stops stretching and springs back on itself, it will shrink until galaxies start colliding in the Big Crunch - terminating in the mother of all black holes. OR The final scenario involves the Universe gradually slowing down to a halt. Eventually the Universe would succumb to the Big Freeze, it would just take a lot longer. But before that , in about 4 billion years the Sun will expand and engulf our planet Earth (become huge, a red giant). Also around the same time, our nearest galactic neighbor, Andromeda, will start to crash into our own galaxy, the Milky Way. Life on Earth must escape into space if it is to survive. This is what it will look like when the universe collides on itself resulting into a Big Crunch