The Galaxy , – in Space
What is galaxy?
A galaxy is massive group of hundreds of millions ofstars , all held together by gravity, orbiting around a common centre.
The Milky Way is the galaxy in which our Sun ,Earth , and planets exist.All stars visible to the naked eye from the Earth also belong to our galaxy, the Milky Way . Our Sun is just a star in Milky Way .There are billions of galaxies in the Universe . Some galaxies are small having only million stars , while some other could have as many as 500 billion stars , or even more .
Why is the Milky Way special to us?
The Milky Way is the galaxy in which our Sun, Earth, and planets exist .
The Milky Way is shaped like huge whirlpool or spiral that rotates once every 200 million years .
It is made up of at least 100 billion stars , as well as dust and gas . It is so big that light takes 1,00,000 years to cross from one side to the other!
Scientists think that the centre of the galaxy contains a super massive black hole that swallows anything passing too close . The Sun and its planets , including our Earth, lie in the quiet part of Milky Way, about half way out from the centre.
How are galaxies born ?
Scientists believe that clumps of gas joined together to form young galaxies called protogalaxies. These protogalaxies developed in different ways. Some had huge clumps of gas at the centre , which formed massive explosion. Many massive explosions are forced the gas remained . So , only the stars formed in this manner become elliptical galaxies.
Sometimes a protogalaxy will contain only small clumps of gas . Since it’s centre will be smaller , there will be fewer massive explosions. Most of the gas is retained along with the stars that have formed , and the galaxy become a spiral galaxy.
Irregular galaxies are probably protogalaxies in which explosions are still going on .
What is a solar system?
The solar system consists of the Sun , and
everything that revolves round it . The Sun, eight planets including our Earth, on which we are living , their moons
are satellites, asteroids or moons planets , and millions of comets and meteoroids make up the solar system.
The Sun is the faint of the solar system. The mass of the Sun is much more than masses of all the planets put together.
Therefore, it occupies the centre of the solar system.
The word ‘solar’ means ‘related to the Sun’ . There may be many solar systems in the Universe.
Our neighbours: Though there are billions of galaxies in the Universe, only three of them can be seen from the Earth through a telescope. They appear as small patches of light . The Andromeda galaxy is one of the nearest large galaxies, which is about 2.2 million light years away.
Spiral Milky Way : All galaxies do not look alike . There are three main types of galaxies spiral , elliptical, and irregular. Our galaxy, the Milky Way is spiral galaxy.
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