In spectroscopy, they analyze the light itself. Most telescopes are equipped with cameras that record images showing the relative brightness of a satellite's surface areas. A change in brightness in an area may indicate geologic activity, such as volcanic eruptions. Scientists photograph most satellites in black and white through a special light filter. To create a color picture, they combine several images taken with different colored filters.
Spectroscopy breaks up the sunlight reflected from a satellite into the light's individual colors.
The colors form a rainbowlike band called a spectrum. Every chemical element absorbs and reflects certain wavelengths of light, producing an individual spectral pattern. By studying a satellite's spectral patterns, scientists can identify its chemical elements and determine whether the elements are solids, liquids, or gases. They can also measure its temperature. See Light .