SATELLITE OBSERVATORY

Earth-orbiting spacecraft that makes it possible to observe cosmic objects and detect radiation from above the atmosphere. Modern astronomers use such observatories to avoid the problems of atmospheric absorption and atmospheric seeing. Absorption by molecules and atoms in the upper atmosphere effectively blocks all but visible light, radio waves, and some infrared radiation from reaching the Earth's surface. In the phenomenon of seeing (q.v.), visible images of celestial objects appear to be blurred or unstable as a result of turbulence in the lower part of the atmosphere. An observatory in space can potentially detect all electromagnetic frequencies, but different instruments are needed for different parts of the spectrum. Since the early 1970s, many countries have launched satellite observatories. The Infrared Astronomical Satellite has mapped the sky in the infrared region, and the International Ultraviolet Explorer has studied faint objects in the ultraviolet region. In the optical portion of the spectrum, the Hubble Space Telescope has provided images of unprecedented clarity, while the Roentgen Satellite and the Compton Gamma Ray Observatory have permitted the investigation of X-ray and gamma-ray sources, respectively. Other satellite observatories, such as the Orbiting Solar Observatories, have been specially designed for studying the Sun, usually at many wavelengths simultaneously. Still other observatories have been designed to detect cosmic-ray particles.