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Distant stars and galaxies are too far away for us to reach. We cannot go to them to study them. So everything we know about distant stars and galaxies comes from analysing the radiation they produce.

Telescopes are devices used to observe the universe. There are many different types and some are even sited in space.

Optical telescopes

Optical telescopes observe visible light from space. Small ones allow amateurs to view the night sky relatively cheaply but there are very large optical telescopes sited around the world for professional astronomers to use.

Optical telescopes on the ground have some disadvantages:

• They can only be used at night.
• They cannot be used if the weather is poor or cloudy.