We hear much news about the Hubble Space Telescope (HST) and, sometimes, it seems that it is the only telescope in space. However, it is not. HST, like other space observatories, is an instrument launched into outer space that is used by astronomers to observe planets, stars, galaxies, and other space objects.
Many space telescopes have been launched into space in the past, and now in the present. Some of the early space telescopes include the Infrared Astronomical Satellite (IRAS), Röntgen Satellite (ROSAT), Copernicus, and Uhuru (X-ray Explorer Satellite).
These space telescopes use electromagnetic radiation—self-propagating waves with electric and magnetic components—that are emitted by celestial objects. Visible radiation, or light that we see, is the most common form of electromagnetic radiation but many other forms of electromagnetic (sometimes abbreviated EM) radiation exist in different forms depending on the size of their wavelength. These forms include: radio, microwave, infrared, visible, x ray, and gamma ray.
Radio wave radiation has the longest wavelength, with a range from a few millimeters to about 50,000 kilometers. Gamma-ray radiation occurs at the wavelength range of 0.01 nanometers and less—the shortest wavelength of all radiation. Of all the many different space telescopes in operation today, each one operates in a specific range within the electromagnetic spectrum. HST observes mostly with visible radiation (from about 360 to 780 nanometer), but also uses UV radiation that is slightly shorter in wavelength, and IR radiation that is slightly longer in wavelength, than visible radiation.
The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite that uses microwave radiation to measure the temperature of heat left over from the Big Bang, the theory on the origin of the universe. Microwaves range from 30 centimeters to about 1 millimeters in wavelength. In 2003, NASA announced that WMAP had captured a photograph of the early universe that showed first-generation stars, which first formed only about 200 million years after the Big Bang. WMAP also pinpointed the age of the universe at about 13.7 billion years old.
The Spitzer Space Telescope (SST) is an infrared (IR) radiation observatory—launched by NASA in August 2003—which possesses a heliocentric (Sun-centered) orbit rather than the traditional geocentric (Earth-centered) orbit. IR radiation comes in a range of wavelengths from 750 nanometers to 1 millimeter. In 2005, SST observed the light from an extrasolar planet, the first direct radiation from a planet orbiting a star other than the Sun. SST has also observed blobs of light from stars that formed only 100 million years after the Big Bang, other infant stars in the early universe.
The Galaxy Evolution Explorer (GALEX), launched by NASA in April 2003, makes observations with ultraviolet radiation (about 400 nanometers to 1 nanometer in wavelength) to measure star and galaxy formation in the early universe, galactic distances, and star formation rates. In all, GALEX will develop a history of star formation for the first three-quarters of the universe, in all about 10 billion years.
X-ray radiation occurs in a wavelength range of 10 to 0.01 nanometers. Two telescopes that use x rays include the X-ray Multi-Mirror Newton (XMM-Newton), which was launched by the European Space Agency in December 1999 and is expected to remain in operation until 2010, and the Chandra X-ray Observatory (Chandra), which was launched by NASA in July 1999 and is still functioning nominally in space.
The Space Shuttle Discovery will fly to Hubble on one of its last missions to service the ailing telescope. If successful, the Hubble’s useful life will be extended to at least 2013. In that year, the James Webb Space Telescope (JWST) is scheduled to be launched as the replacement for Hubble. However, the JWST will observe only in the infrared region of the EM radiation spectrum, and not also in the visible and ultraviolet parts, like Hubble.
As you can see, the Hubble Space Telescope only operates at one small region within the electromagnetic spectrum. Many other telescopes are currently operating at other regions so that most forms of radiation are being studied. Even though the Hubble Space Telescope will eventually be decommissioned, many other telescopes are now in use or will soon be in use to continue to scan the universe looking with eyes that are specifically sensitive to a particular range of radiation within the electromagnetic spectrum. Hubble has been very important to the advancement of astrophysics and cosmology, but it is just one of many space telescopes. Like people, Hubble will live a useful life but eventually it will be replaced by a new generation of space telescopes.
(published in Helioza on January 6, 2007)
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