The Universe
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14. Sun, stars and galaxies

Figure 10.28 Different type of galaxies
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galaxy is a group of stars and other space stuff, like interstellar gas and dust.

Stars are huge celestial bodies, made mostly of hydrogen and helium, that produce light and heat from nuclear fusion reactions.

The stars tend to spin around a centre of high gravity, like the planets spin around the Sun in the Solar System.

Galaxies are huge and can have trillions of stars. Each star can often have their own planetary systems.

As big as galaxies are, they are generally separated by large areas of empty space.

There are even clusters of galaxies that are separated by even larger areas of space. Scientists think there are over 100 billion galaxies. The universe is huge!

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