Telescopes
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 telescopeA device used to see distant objects more clearly. An optical telescope receives and refracts visible light using an arrangement of lenses. 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.
Other telescopes
radio-telescopeA telescope that detects the Radio wave part of the EM spectrum. Often used to detect signals from other star systems and space. detect radio waves coming from space. Although they are usually very large and expensive, these telescopes have an advantage over optical telescopes. They can be used in bad weather because the radio waves are not blocked by clouds as they pass through the atmosphere. Radio telescopes can be used in daytime as well as at night.
X-rays are partly blocked by the Earth's atmosphere and so X-ray telescopes need to be at high altitude, flown in balloons or carried in satellites above the Earth's atmosphere.
Space telescopes
Objects in the universe emit other electromagnetic radiation such as infraredRadiation which transfers heat energy. Part of the electromagnetic spectrum with a longer wavelength than light waves but a shorter wavelength than radio waves., X-rays and gamma rays. These are all blocked by the Earth's atmosphere, but can be detected by telescopes placed in orbit round the Earth.
Telescopes in space can observe the whole sky and they can operate both night and day. However, they are difficult and expensive to launch and maintain. If anything goes wrong, sometimes only astronauts can repair them.