Ground Telescopes

Very Large Telescope
The moon setting behind the Very Large Telescope in Chile

Most of the telescopes used by astronomers are known as ground-based, this means that they are located here on Earth at some of the best observing sites in the world.

It is obviously easier to have a telescope here on Earth as it can be visited much more frequently and is much easier to fix if things go wrong, it is also substantially cheaper to build. However, there are down sides as well. When a telescope is placed on the ground it has to look up through the Earth's atmosphere to see into space, and the atmosphere can blur our images.

The atmosphere also blocks out light from certain parts of the electromagnetic spectrum, this means we cannot see this light from the ground and instead need to put a telescope into space to get this information.

The gaps in our atmosphere where light is able to get through to the ground are called atmospheric windows and they can be seen below where the opacity, or how much light is let through, is 0% (transparent to the light), or a low number (translucent to light). Where the opacity is 100% no light of that wavelength can get through, or it is opaque to that light.

Atmospheric Windows
The opacity of the Earth's atmosphere to light of different wavelengths.
Credit: NASA