An optical telescope is the type with which most people are familiar, the kind one looks through in the backyard. The only type of radiation it detects is visible light, meaning it sees what the human eye sees except magnified many times. Other types of telescopes are used to observe radiation from other regions of the electromagnetic spectrum. For example, infrared telescopes detect infrared radiation, and radio telescopes detect radio waves. Other telescopes, placed onboard satellites, study ultraviolet radiation, X-rays, and gamma rays in space. The two main types of optical telescopes are refractors and reflectors.
