Universe – The Beginning 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. Astronomers are now fairly sure that the Universe was born 15 billion years ago due to the Big Bang.

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. 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! 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.

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. 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. 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. 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!

Beyond the Solar System When a large star has burnt all its fuel, it explodes into a Supernova. The stuff that is left becomes extremely dense to form a ‘Neutron Star’. If this Neutron Star is too large, it exerts a tremendous gravitational pull towards the center due to which it starts imploding further and becomes even denser. It becomes so dense that due to its gravity even light cannot escape it. Hence a black hole is a region in space-time from which nothing can escape. The black holes cannot be seen but its presence can be known using the radio telescopes. Halley’s Comet Our Solar System was a vast cloud of gas and dust billions of years ago. Comets are made of the same material, which formed a part of cosmos at that time. The comets consist of the chunks of hydrogen, ice and dust which then escaped the gravitational pull of the Sun as it was being formed. These leftover masses of the cosmic material then started orbiting round the Sun These are called Comets. A comet has nucleus comprising hydrogen cornea and a tail of dust and gas. Many comets have been discovered using powerful telescopes available nowadays. The most famous comet is the Halley’s Comet which was last seen in It orbits round the Sun and appears once in 75 years. As such, it is expected to pass the solar system in the year This picture is a Nebula Nebula is the Latin word for ‘cloud’. It is a cosmic cloud of gas and dust floating in space. The Nebulae are the basic building blocks out of which stars and solar systems have been made. Bulk of the Nebulae consists of hydrogen and helium with a small percentage of heavy metals. It is then presence of these metals that give the nebulae different colours. Nebulae are very vast. Sometimes these extend to thousands of light years in extent.

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