III.

Types of Space Telescopes

The Hubble Space Telescope is a general-purpose observatory that can detect different types of electromagnetic radiation from infrared to ultraviolet. However, most space telescopes are designed to study a particular range of wavelengths on the electromagnetic spectrum. The major divisions of the spectrum from longest to shortest wavelength are: radio, microwave, infrared, visible light, ultraviolet radiation, X ray, and gamma ray. Radio waves easily penetrate Earth’s atmosphere, so radio telescopes can be ground-based.

A.

Microwave Space Telescopes

Space telescopes that detect microwaves are used to study the earliest stages of the universe after the big bang 13.7 billion years ago. See also Background Radiation; Big Bang Theory.

B.

Infrared Space Telescopes

Earth’s atmosphere emits infrared radiation, called infrared background glow, which interferes with readings by ground-based infrared telescopes. The atmosphere also contains water vapor that absorbs some infrared radiation, preventing it from reaching ground-based infrared telescopes. Infrared telescopes in space are not hampered by background glow and are extraordinarily sensitive to faint infrared sources. See also Infrared Astronomy; Infrared Space Observatory; Spitzer Space Telescope; James Webb Space Telescope.

C.

Visible-Light Space Telescopes

Visible-light observations from space have the advantage of a clearer image. Ground-based telescopes are hampered by interference by Earth’s atmosphere, which produces fuzzy images. Space telescopes designed to detect visible light have been used to study galaxies, stars, planets, and objects in the solar system. See also Hubble Space Telescope.

D.

Ultraviolet Space Telescopes

Some of the hottest and most energetic stars in the universe are visible in the ultraviolet region of the electromagnetic spectrum. Sources include the atmospheres of young stars, the surfaces of hot white dwarf stars and the cores of active galaxies. See also Ultraviolet Astronomy.

D.1.

X-Ray Space Observatories

Earth’s atmosphere absorbs almost all the X rays that enter it from space. X rays are often associated with high-energy events that are of interest to astronomers. Supernovas (stars that explode at the end of their lives) and the centers of active galaxies emit X rays. X rays are also emitted by binary star systems in which the gravitational pull of a small, dense star such as a white dwarf (a very compact, small star) or a neutron star (the collapsed remnant of a massive star) is pulling gas off of its normal companion star and heating it to millions of degrees. See also X-Ray Astronomy; Chandra X-Ray Observatory.

D.2.

Gamma-Ray Space Observatories

Studying gamma rays offers scientists answers to some of the most perplexing questions about the explosive and dynamic physical processes in the universe. Gamma-ray observation also provides clues about the structure and dynamics of the Milky Way and other galaxies; the nature of pulsars, quasars, black holes, and neutron stars; and the origin and history of the universe itself. See also Gamma-Ray Astronomy; Compton Gamma Ray Observatory.