Light and telescopes

The universe is full of amazing things, but we need help to see most of them. There are many types of light that our eyes cannot see, so we use instruments, such as telescopes, that can detect this hidden light.

About light

Most objects in space give off (radiate) light. This light is given different names, depending on its wavelength and energy – radio waves (long wavelength, low energy), microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays (short wavelength, high energy). Scientists call the whole range of light types the electromagnetic spectrum. They don’t use the word ‘light’ because most of us think of light as just what we can see with our eyes. Get used to using the scientific term electromagnetic spectrum when talking about light.

Our eyes only see a very small part of the electromagnetic spectrum, so we need special instruments to detect the rest. Even though you may not be able to see certain wavelengths, you will have experienced them in one way or the other:

• Radio waves – you can’t see them, but you’ve listened to the radio.
• Microwaves – you may have used them to heat your food.
• UV – can give you sunburn.
• X-rays – reveal broken bones.

Even though you can’t see them with your eyes, they are there, and we use different instruments to make them visible.

Most objects in space give off several types of electromagnetic radiation at the same time. What they radiate depends on many things, such as how hot they are and what they are made of. Astronomers collect information about the radiation from space objects to find out about such things as the births and deaths of stars, how hot objects are, how far away they are, even how the universe was formed.

Telescopes and the electromagnetic spectrum

Astronomers use telescopes that detect different parts of the electromagnetic spectrum. Each type of telescope can only detect one part of the electromagnetic spectrum. There are radio telescopes, infrared telescopes, optical (visible light) telescopes and so on.

We can’t see most of the radiation detected, so computers turn data into images we can see. Many of the images you see of space have amazing colours – these are called false colours because computers have taken the data from wavelengths we can’t see and presented them as colours we can see.

Astronomers have a huge problem detecting radiation from space because the Earth’s atmosphere blocks most of it and stops it from reaching the surface. Visible light and radio waves get through to telescopes on the ground, and some detectors (infrared, UV and gamma) work when they are high up on mountains. The best place to detect most radiation is above the blocking atmosphere, so some telescopes are put in orbit around the Earth. Even visible light is distorted by the atmosphere, so clearer pictures can be got from orbiting telescopes. For example, the Hubble Space Telescope is positioned outside the Earth’s atmosphere and takes very sharp images of very distant objects in space.