Hubble Space Telescope is a reflecting telescope built as an orbiting observatory. Its main light-gathering mirror measures 94 inches (240 centimeters) in diameter. The United States space agency, the National Aeronautics and Space Administration (NASA), administers the telescope. NASA launched the Hubble Space Telescope on a space shuttle in 1990.

The Hubble telescope is controlled by radio commands from NASA's Goddard Space Flight Center in Greenbelt, Maryland. The telescope transmits data by radio to astronomers on the ground. It is named for American astronomer Edwin P. Hubble.

The Hubble telescope orbits the earth about 380 miles (610 kilometers) above the surface, enabling it to escape the effects of the earth's atmosphere. The atmosphere bends light from the stars and galaxies, and so it blurs images. But the Hubble telescope produces significantly sharper images and observes objects 50 times fainter than telescopes on the earth can. It can also study ultraviolet and infrared light that is blocked by the earth's atmosphere. These forms of light, like visible light, consist of electromagnetic radiation. The wavelength (distance between successive wave crests) of ultraviolet light is shorter than that of visible light. Infrared light has longer wavelengths than visible light.

Astronomers have used the Hubble telescope to find evidence for massive black holes. They also have made images of Pluto, the most distant planet in the solar system, and of a satellite of Pluto called Charon. In addition, the telescope has shown that at least half the young stars in the Great Nebula are surrounded by disks of dust and gas that may form planets. The Great Nebula is a cloud of dust particles and gas in the Orion constellation.

Excerpt from the "Hubble Space Telescope" article, The World Book Encyclopedia © 1999