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Infrared Astronomy

Infrared astronomy

Infrared astronomy involves the use of special telescopes that detect electromagnetic radiation (radiation that transmits energy through the inter-action of electricity and magnetism) at infrared wavelengths. The recent development of this technology has led to the discovery of many new stars, galaxies, asteroids, and quasars.

Electromagnetic spectrum

Light is a form of electromagnetic radiation. The different colors of light that our eyes can detect correspond to different wavelengths of light. Red light has the longest wavelength; violet has the shortest. Orange, yellow, green, blue, and indigo are in between. Infrared light, ultraviolet light, radio waves, microwaves, and gamma rays are all forms of electromagnetic radiation, but they differ in wavelength and frequency. Infrared light has slightly longer wavelengths than red light. Our eyes cannot detect infrared light, but we can feel it as heat.

Infrared telescopes

Two types of infrared telescopes exist: those on the ground and those carried into space by satellites. The use of ground-based telescopes is somewhat limited because carbon dioxide and water in the atmosphere absorb much of the incoming infrared radiation. The best observations are made at high altitudes in areas with dry climates. Since infrared telescopes are not affected by light, they can be used during the day as well as at night.

Words to Know

Dwarf galaxy: An unusually small, faint group of stars.

Electromagnetic radiation: Radiation that transmits energy through the interaction of electricity and magnetism.

Infrared detector: An electronic device for sensing infrared light.

Infrared light: Portion of the electromagnetic spectrum with wavelengths slightly longer than optical light that takes the form of heat.

Optical (visible) light: Portion of the electromagnetic spectrum that we can detect with our eyes.

Quasars: Extremely bright, starlike sources of radio waves that are the oldest known objects in the universe.

Redshift: Shift of an object's light spectrum toward the red-end of the visible light rangean indication that the object is moving away from the observer.

Stellar nurseries: Areas within glowing clouds of gas and dust where new stars are formed.

Space-based infrared telescopes pick up much of the infrared radiation that is blocked by Earth's atmosphere. In the early 1980s, an international group made up of the United States, England, and the Netherlands launched the Infrared Astronomical Satellite (IRAS). Before running out of liquid helium (which the satellite used to cool its infrared detectors) in 1983, IRAS uncovered never-before-seen parts of the Milky Way, the galaxy that's home to our solar system.

In 1995, the European Space Agency launched the Infrared Space Observatory (ISO), an astronomical satellite. Before it ran out of liquid helium in 1998, the ISO discovered protostars, planet-forming nebula around dying stars, and water throughout the universe (including in the gas giants like the planets Saturn and Uranus).

In mid-2002, the National Aeronautics and Space Administration (NASA) plans to launch the Space Infrared Telescope Facility (SIRTF), which will see infrared radiation and peer through the veil of gas and dust that obscures most of the universe from view. It will be the most sensitive instrument ever to look at the infrared spectrum in the universe. SIRTF researchers will study massive black holes, young dusty star systems, and the evolution of galaxies up to 12 billion light-years away.

Discoveries with infrared telescopes

Infrared telescopes have helped astronomers find where new stars are forming, areas known as stellar nurseries. A star forms from a collapsing cloud of gas and dust. Forming and newly formed stars are still enshrouded by a cocoon of dust that blocks optical light. Thus infrared astronomers can more easily probe these stellar nurseries than optical astronomers can. The view of the center of our galaxy is also blocked by large amounts of interstellar dust. The galactic center is more easily seen by infrared than by optical astronomers.

With the aid of infrared telescopes, astronomers have also located a number of new galaxies, many too far away to be seen by visible light. Some of these are dwarf galaxies, which are more plentifulbut contain fewer starsthan visible galaxies. The discovery of these infrared dwarf galaxies has led to the theory that they once dominated the universe and then came together over time to form visible galaxies, such as the Milky Way.

With the growing use of infrared astronomy, scientists have learned that galaxies contain many more stars than had ever been imagined. Infrared telescopes can detect radiation from relatively cool stars, which give off no visible light. Many of these stars are the size of the Sun. These discoveries have drastically changed scientists' calculations of the total mass in the universe.

Infrared detectors have also been used to observe far-away objects such as quasars. Quasars have large redshifts, which indicate that they are moving away from Earth at high speeds. In a redshifted object, the waves of radiation are lengthened and shifted toward the red end of the spectrum. Since the redshift of quasars is so great, their visible light gets stretched into infrared wavelengths. While these infrared wavelengths are undetectable with optical telescopes, they are easily viewed with infrared telescopes.

[See also Electromagnetic spectrum; Galaxy; Spectroscopy; Star; Starburst galaxy ]

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infrared astronomy

infrared astronomy, study of celestial objects by means of the infrared radiation they emit, in the wavelength range from about 1 micrometer to about 1 millimeter. All objects, from trees and buildings on the earth to distant galaxies, emit infrared (IR) radiation. The study of such radiation from celestial objects is of particular importance for several reasons. Cosmic dust particles effectively obscure parts of the visible universe, such as the center of our galaxy, the Milky Way, but this dust is transparent in the IR wavelengths. Most of the energy radiated by objects ranging from interstellar matter to planets lies in the IR wavelengths; IR observations are therefore significant in studying asteroids, comets, planetary satellites, and interstellar dust clouds where stars are forming. Finally, because the expansion of the universe shifts energy to longer wavelengths, most of the visible radiation emitted by stars and galaxies during the early stages of the formation of the universe is now shifted to the IR range; studies of the most distant objects in the IR spectrum are necessary if astronomers are to understand how the universe was formed.

The beginnings of IR astronomy can be traced to the discovery of IR radiation in the spectrum of the sun by English astronomer Sir William Herschel about 1800. It is reported that Irish astronomer Lord William Rosse detected IR radiation from the moon about 1845. As early as 1878 the American inventor Thomas Alva Edison observed a solar eclipse from a site in Wyoming using a sensitive IR detector, and during the 1920s the first systematic IR observations of celestial objects were made by Seth B. Nicholson, Edison Pettit, and other American astronomers. However, modern IR astronomy did not begin until the 1950s because of the lack of appropriate instrumentation. Since then, special interference filters and cryogenic systems (to minimize IR interference from the radiation emitted by the equipment itself) have been introduced for ground-based observations, and aircraft, balloons, rockets, and orbiting satellites have been successively employed to carry the equipment above the water vapor in the earth's atmosphere.

The Kuiper Airborne Observatory (KAO), operated by the National Aeronautics and Space Administration (NASA), had its first flight in 1975. Named for the American astronomer Gerard P. Kuiper, the KAO was a C-141 jet transport that carried its 36-inch (91-cm) telescope to altitudes of up to 45,000 ft (13,720 m). Before it flew its last mission in 1995, the KAO was instrumental in the discovery of the rings of Uranus, the atmosphere around Pluto, and the definitive detection of water during the crash of comet Shoemaker-Levy 9 into Jupiter. Also sponsored by NASA is the Infrared Telescope Facility, a 10-ft (3-m) IR telescope located at an altitude of 14,000 ft (4,270 m) on the summit of Mauna Kea in Hawaii; established in 1979, it effectively is the U.S. national IR observatory. Also near the summit of Mauna Kea is the 12.5-ft (3.8-m) United Kingdom Infrared Telescope (UKIRT), the largest telescope in the world used solely for IR observations.

The first IR satellite to be launched (1983) was the Infrared Astronomical Satellite (IRAS), a joint venture of the United States, Great Britain, and the Netherlands. Orbiting the earth for 10 months, IRAS performed an all-sky survey that yielded catalogs of hundreds of thousands of IR sources, more than half of these previously unknown, including asteroids and comets; detected a new class of long-lived "cool" galaxies that are dim in the visible region of the spectrum; located a protoplanetary disk around a nearby star; and showed clearly for the first time the bulge near the center of the Milky Way. In 1989 the second IR satellite, the Cosmic Background Explorer (COBE), was launched by NASA. Operating through 1993, COBE detected small temperature variations in the cosmic microwave background radiation that provided vital clues to the nature of the early universe and its evolution since the "big bang." The European Space Agency (ESA) launched the Infrared Space Observatory (ISO) in 1995. Operating until May, 1998, ISO monitored nearby planets, asteroids, and comets. It found water vapor in the atmospheres of Saturn, Neptune, Uranus, and Titan, Saturn's largest moon; detected water vapor and fluorides in the interstellar medium; and studied the "cool" galaxies first seen by IRAS. The near-infrared camera multiobject spectrometer (NICMOS) was placed aboard the Hubble Space Telescope in 1997. Consisting of three cameras and three spectrometers, it has been used to study interstellar clouds where stars are being formed, young stars, and the atmospheres of Jupiter and Uranus.

The Spitzer Space Telescope, a cryogenically cooled satellite observatory with a 2.8-ft (0.85-m) telescope, was launched in Aug., 2003, and placed in a solar orbit in which it trails the earth by 5.4 million mi (8.7 million km); the lifetime of its main instruments ended in 2009. In May, 2009, ESA launched the Herschel Space Telescope, with a 138-in. (3.5-m) mirror; it also was cryogenically cooled. Positioned some 930,000 mi (1.5 million km) from earth on a mission that lasted until 2013, it observed wavelengths from the infrared to the submillimeter. NASA's Wide-field Infrared Survey Explorer (WISE) was launched in Dec., 2009, on a six-month mission to survey the entire sky at infrared wavelengths. A KAO replacement, the Stratospheric Observatory for Infrared Astronomy (SOFIA), flew its first official science mission in 2010. Consisting of a Boeing 747-SP aircraft modified to accommodate a 8.2-ft (2.5-m) reflecting telescope (the largest airborne telescope in the world), it is a joint project of NASA and the German space agency, DLR.

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