Let there be light
There are many different forms of light, which together we call the electromagnetic spectrum. Astronomers can now "see" the Universe across the entire spectrum, from radio waves to gamma rays. Many types of light are absorbed or scattered by the Earth's atmosphere, with only narrow optical and radio "windows" open to ground-based observation. To open other windows on the Universe, we must put telescopes in space.
Image credit: www.international-light-association.org