Overview (The Solar System)
Infrared astronomy focuses its study on wavelengths of Electromagnetic radiation that are a little longer than those of visible light. The infrared region of the spectrum covers a wide range of wavelengths from waves slightly longer than those of visible light (0.7 micron, or 0.7 millionth of a meter) to those as long as 1,000 microns. The longest infrared wavelengths are about 1 millimeter in length and mark the boundary with the microwave radio spectrum.
Infrared radiation from distant sources is very difficult to detect. The Sun is so close that the Infrared radiation it emits can be detected in the form of heat. The Moon also emits easily detected infrared radiation. However, to detect emissions from other stars, planets, nebulae, or galaxies, very sensitive detectors are needed. The shortest infrared waves are known to astronomers as the “photographic infrared” because they are very similar to visible light and can be detected with certain types of photographic emulsions and other types of optical detectors. At longer wavelengths of infrared radiation, objects can be detected that are not visible at optical wavelengths. Nevertheless, at these wavelengths, the detectors used for the photographic infrared are no longer useful.
Modern infrared detectors often use a substance called indium antimonide, which changes its electrical conductivity when exposed to infrared radiation. In order to be effective, however, it...
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Applications (The Solar System)
Infrared radiation can give astronomers valuable information about the formation of stars. Stars are believed to be formed from large clouds of rotating dust and gas that condense under their own gravity. Energy released in the collapse causes the forming star, or “protostar,” to increase in temperature until nuclear reactions begin. It is not until the star “turns on” in this way that it begins to emit radiation in visible wavelengths. As a result, the process of star formation is difficult to study optically. As the star begins to shine, newly created energy warms the surrounding dust, which radiates the energy away as infrared waves. The process is still not understood completely, and astronomers have learned much by the study of infrared and radio wavelengths.
Many infrared sources are clouds of dust heated by a nearby star. Infrared stars generally are either very young or very old stars, those that are associated with dust clouds. One of the early infrared discoveries was of a giant cloud of gas and dust in the Constellation of Orion: the Kleinmann-Low nebula, named for its discoverers. It was found to have a mass greater than two hundred times that of the Sun, yet it is invisible at optical wavelengths. In the infrared, it outshines the Sun more than 100,000 times. It was determined to be a relatively close area of active star formation (within 1,600 light-years). Detailed studies of the Kleinmann-Low Nebula in...
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Context (The Solar System)
Infrared astronomy is part of the Revolution that has been called the “new astronomy.” Instruments of modern astronomers give them access to information from the entire range of the electromagnetic spectrum. This revolution has occurred mostly since the early 1960’s, when it became possible to place remote detectors above Earth’s atmosphere. Before then, astronomers relied for the most part on the optical range of wavelengths for their information about the universe.
It was not until 1800 that the first sign of another way to look at the universe was discovered. While analyzing sunlight by separating the white light into a spectrum, English astronomer Sir William Herschel noticed that a thermometer placed in the dark area just outside the red limit of the spectrum registered an increase in temperature. In 1881, American astronomer Samuel Pierpont Langley developed the bolometer, an electrical detector that measures heat over a broad range of wavelengths. In measuring the Sun’s energy from a high altitude, Langley found that the Radiant energy of the Sun extended far past the visible portion of the spectrum and far past the region that Herschel had discovered previously. Herschel had discovered the near-infrared, whereas Langley was detecting the longer-wavelength middle-infrared band.
Infrared radiation from the Sun was fairly simple to detect, but more sensitive instruments had to be developed before it was possible...
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Further Reading (The Solar System)
Chaisson, Eric, and Steve McMillan. Astronomy Today. 6th ed. New York: Addison-Wesley, 2008. This traditional treatise on introductory astronomy includes up-to-date spacecraft information such as that from NASA’s Great Observatories program and rovers on Mars. Includes images that span the electromagnetic spectrum.
Dinwiddie, Robert, et al. Universe. New York: DK Adult, 2005. A remarkable collection of articles written by science writers and professional astronomers on a wide range of topics that span the discipline of astronomy. Heavily illustrated and filled with high-quality photographs. For the general reader.
Gregory, Stephen A. Introductory Astronomy and Astrophysics. 4th ed. San Francisco: Brooks/Cole, 1997. Suitable as a textbook for an introductory college-level or advanced high school course in general astronomy. Covers all topics from solar system bodies to cosmology. Some errors and issues with mathematical presentations.
Henbest, Nigel, and Michael Marten. The New Astronomy. New York: Cambridge University Press, 1983. Compares optical, infrared, ultraviolet, radio, and X-ray observations of well-known astronomical objects. For general readers.
Karttunen, H. P., et al., eds. Fundamental Astronomy. 5th ed. New York: Springer, 2007. A well-used university textbook in introductory astronomy. Contains some calculus-based treatments for those who find...
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Infrared Astronomy (Encyclopedia of Science)
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.
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.
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...
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