NASA's Great Observatories Hubble Compton Chandra SIRTF
400th Anniversary of the Telescope »»
 Gemini South Telescope in Chile |
For most people a telescope is an optical telescope, which lets an astronomer see objects in space that radiate or reflect visible light. However, much of what can be seen across the Universe is invisible to human eyes because we see only the visible light portion of the electromagnetic spectrum.
Stars, galaxies, black holes, pulsars, quasars and other objects strewn across deep space emit lots of energy elsewhere in the electromagnetic spectrum. Astronomers use radio, infrared, ultraviolet, X-ray and gamma-ray telescopes to look at those invisible emissions to gain a better understanding of the Universe.
Each kind of telescope tunes in a different wavelength of energy along the electromagnetic spectrum. Many celestial phenomena can be seen at more than one wavelength.
- Optical telescopes can be used on Earth and in space. An example of a huge optical telescope in space is the Hubble Space Telescope through which astronomers can look out across the Universe without the distortion of light by the Earth's atmosphere. The first optical telescope was created 400 years ago, while the other kinds of telescopes were invented in the 20th century.
- Radiotelescopes also can be used on Earth or in space. An example of a radiotelescope on Earth is the Very Large Array of 27 antennas sprawling across New Mexico. Radio signals received from deep space received by the VLA are combined electronically to create a virtual antenna 22 miles across.
- Infrared telescopes are affected by Earth's atmosphere. They have to be at high altitudes, above water vapor in the atmosphere, or else out in space. Frequently they are on mountaintops. The large Space Infrared Telescope Facility (SIRTF) was to be launched in 2003. Hubble also observes in infrared light.
- Ultraviolet telescopes also are affected by the atmosphere. They have to be at even higher altitudes than infrared telescopes. Earth's ozone layer is in the stratosphere some 12-24 miles above the surface. The ozone layer blocks most ultraviolet (UV) light. Earth's atmosphere absorbs UV, protecting life on the surface from its damaging effects. Telescopes designed to see UV must be above the atmosphere. Hubble also observes in ultraviolet light.
- X-ray telescopes also must be above the atmosphere. X-rays are considered high energy and Earth's atmosphere protects us from their damaging effects. NASA's first X-ray telescope was the satellite Uhuru — Swahili for freedom — launched from the African nation of Kenya on Dec. 12, 1970, the seventh anniversary of Kenya's independence. The large Chandra X-ray Observatory was launched in 1999.
- Gamma-ray telescopes also must be above the atmosphere. Gamma rays also are considered high energy and Earth's atmosphere protects life on the surface. Explorer XI, the first gamma-ray telescope satellite, was launched in 1961. The large Compton Gamma Ray Observatory was launched to space in 1991.
400th Anniversary of the Telescope »»
NASA's Great Observatories »»Hubble Compton Chandra SIRTF
Swift Gamma-Ray Burst Observatory »»
Gemini South Telescope Twin in Chile »»
Southern African Large Telescope »»
James Webb Space Telescope »»
Lovell Telescope at Jodrell Bank Observatory »»
Ulug'bek's Great Observatory at Samarkand »»
Ancient Linfen Observatory in Northern China »»
The Nassau Astronomical Station »»
Remote Control Telescope on the Internet »»
The Puckett Private Observatory »»
NASA's Deep Space Network »»
Using a Telescope in Your Backyard »»
Lightyears »»