How do modern telescopes work?
Telescopes gather light in one of two ways. Reflecting telescopes focus light with a series of mirrors, while refracting telescopes use lenses. For research purposes, reflecting telescopes have become the standard because of the relative ease of constructing and working with large mirrors. The lenses needed for refracting telescopes present endless engineering problems and must be extremely pure throughout their entire volumes, while mirrored surfaces require ultra-fine precision only on the surface.
Modern telescopes gather information from the electromagnetic spectrum far beyond the range of visible light. Telescopes that survey radio, x-ray, and gamma-ray wavelength have dramatically broadened our understanding of the universe. Radio telescopes -- huge wire-mesh dishes designed to focus radio signals from space -- have helped to map the spiral arms of our galaxy, while gamma-ray observatories high in Earth orbit have captured the high-energy signals of exotic objects such as black holes and gamma-ray bursts.
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