People who know a lot about astronomy and different types of light?

Well light comes in many different forms or wavelengths than just visible light or what you can see. Problem is, our eyes are only sensitive enough to see visible light. Spectrometers used in space can gather light from a distant object in space and use a prism to seperate the different wavelengths. They can measure these wavelengths. When a star is behind a distant planet, some of the light from the star will shine through the atmosphere of the planet and be directed straight towards earth. When we yze this light after seperating it with a prism there are dark lines ociated with a wavelength of light that is missing. It is missing because and element ociated with that wavelength of light absorbed the light from the star. It also works both ways, a star can shine through a planets atmosphere exciting the atoms of a certain element releasing photons of a specific wavelength ociated with that element and that will also tell us what is in the atmosphere. I hope this helps.