Overview (The Solar System)
Any material with a temperature above Absolute zero emits electromagnetic radiation, and that radiation carries with it information about the nature of the event that produced it. An object will emit radiation over a range of wavelengths, with a concentration at a single wavelength. Very hot objects produce shorter wavelengths, while cooler objects emit longer wavelengths. For example, as metal is heated, it first glows red (the longer wavelengths of visible light), then, as its temperature increases, it begins to glow in the shorter-wavelength yellow light. In space, objects that are very cold, perhaps only a few degrees above absolute zero, will emit radiation in the very long infrared and radio wavelengths. At the other extreme, very hot stars give off ultraviolet radiation, X rays, and gamma rays.
Ultraviolet astronomy focuses on the area of the spectrum that is beyond violet light—the shortest wavelengths the eye can see. The ultraviolet portion of the spectrum begins at a Wavelength of 390 nanometers, ranges to the extreme ultraviolet at 90 nanometers, and merges into the X-ray portion of the spectrum at 10 nanometers.
While the visible portion of the spectrum can be observed from the surface of the Earth, observations at ultraviolet wavelengths must be done outside the Earth’s atmosphere. Ultraviolet radiation is readily absorbed by gases, both in space and in the Earth’s atmosphere. Only the longest...
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Applications (The Solar System)
Each energy region in the electromagnetic spectrum allows astronomers to “see” objects in a unique way. The more information that can be discovered about the nature of a celestial object in each of these energy areas, the more completely the object can be understood.
All objects known to exist in the universe—from comets and planets to stars, galaxies, and quasars—can be effectively studied in the ultraviolet range. Ultraviolet telescopes see the hottest stars of all; as a result, they tend to pick out the youngest star groups in the sky. Ultraviolet astronomy can thus focus on the youthful clusters of stars that lie close to regions of star birth. With this particular window, ultraviolet astronomy has been very useful for mapping regions of star formation, both in the Milky Way and in distant galaxies. Other galactic studies have shown that the Milky Way, as well as other galaxies, surrounded by a hot halo of gas.
There are excellent images of the Sun in the ultraviolet. Views of the ultraviolet Sun reveal different layers of its chromosphere, transition region, and lower corona. Bright, scintillating points of ultraviolet light in the Sun’s atmosphere provide a measure of magnetic activity within the Sun, with perhaps even more accuracy than the Sunspots that are seen on the visible photosphere. By observing other stars in the ultraviolet, astronomers have gained valuable knowledge about the nature of stars,...
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Context (The Solar System)
For thousands of years, the human eye was the only astronomical instrument. The eye evolved to be most sensitive to the range of visible light, the most abundant source of radiation at the surface of the Earth. Any celestial objects that were dim or emitted radiation at mostly nonoptical wavelengths remained invisible to the eye, which limited the range of information about the universe scientists could study.
The invention of the telescope radically altered astronomy, not only because of the fainter objects it allowed astronomers to see but also because it opened up the possibility that there was more to the universe than what the human eye was able to image. Astronomy improved dramatically over the next few centuries but remained optical. The first sign that there was another way to look at the universe with anything other than optical wavelengths came in 1800, when Infrared radiation was discovered by Sir William Herschel, who placed a thermometer just outside the red range of the visible light separated by a prism.
The opening up of the wavelengths of electromagnetic energy got under way with the rapid growth of Radio astronomy in the 1950’s and 1960’s and with the birth of the space program during the same period. The space program allowed ultraviolet astronomy to become an important new area of study. The potential value of ultraviolet observation from space was proposed to the U.S. Air Force in 1946 by the American...
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Further Reading (The Solar System)
Arny, Thomas T. Explorations: An Introduction to Astronomy. 3d ed. New York: McGraw-Hill, 2003. A general astronomy text for the nonscientist. Includes an interactive CD-ROM and is updated with a Web site.
Barstow, Martin A., and Jay B. Holberg. Extreme Ultraviolet Astrophysics. Cambridge, England: Cambridge University Press, 2007. The universe in extreme ultraviolet (EUV) was revealed only when rockets in the late 1960’s sent relatively primitive instruments capable of detecting EUV radiation briefly into space. Those initial investigations demonstrated the universe was rich in EUV-emitting sources. This work catalogs EUV sources, explains the cosmological importance of those sources, and describes the instrumentation that detected them.
Henbest, Nigel. Mysteries of the Universe. New York: Van Nostrand Reinhold, 1981. Explores the limits of what is known about the universe. Discusses theories about the origin of the solar system and the universe, exotic astronomy, and astronomy at invisible wavelengths.
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 need a more advanced textbook than the standard introductory work. Suitable for an audience with varied science and mathematical backgrounds. Covers all topics from...
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Ultraviolet Astronomy (Encyclopedia of Science)
Matter in the universe emits radiation (energy in the form of subatomic particles or waves) from all parts of the electromagnetic spectrum. The electromagnetic spectrum is the range of wavelengths produced by the interaction of electricity and magnetism. The electromagnetic spectrum includes light waves, radio waves, infrared radiation, ultraviolet radiation, X rays, and gamma rays.
Ultraviolet astronomy is the study of celestial matter that emits ultraviolet radiation. Ultraviolet waves are just shorter than the violet end (shortest wavelength) of the visible light spectrum. This branch of astronomy has provided additional information about stars (including the Sun), galaxies, the solar system, the interstellar medium (the "empty" space between celestial bodies), and quasars.
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