Instruments on telescopes are used to make measurements of objects in space.
When astronomers first used telescopes, they looked through them and made drawings or notes of what they saw. When cameras were invented we could save this information as a picture.
The images record what is seen. Modern cameras also let us see more detail. For example, by keeping the shutter on the camera open longer. This gives the image a longer exposure time letting more light reach the telescope. We use this to see fainter objects in space.
Today telescopes have lots of different instruments on them. Each takes a different kind of measurement. They can be attached to the telescope in a number of places. Some are right behind the main mirror. We can also use small mirrors to move the light around and put the instruments in different places. The Liverpool Telescope has 5 instruments which sit at the bottom of the telescope on a carousel. This means it can switch between them quickly.
The most common instruments are cameras. These are CCD cameras which can look at visible or infrared light. Spectrographs are also found on most telescopes. These split up the light into its different colours. They can also look at what an object is made of. They do this by looking for elements which absorb bits of the light.