The Quest To Broaden Our Cosmic View
In their quest to improve our ability to observe the universe,astronomers have followed two lines of technological development. First,they have designed and constructed increasingly powerful telescopes and detectors,capable of observing progressively fainter sources with greater clarity. During the next decade, astronomers will construct telescopes with ever finer resolution, and will also link these instruments to create systems whose observational precision equals that of a single giant telescope as large as the maximum separation of the individual instruments. Second,as a more subtle but equally important way to widen our observational capabilities, astronomers have attempted to study different regions of the spectrum of electromagnetic radiation. This spectrum includes a variety of waves that differ in their wavelengths of vibration.Only a tiny part of the spectrum includes the waves that our eyes can detect.We call these waves "light," and our eyes and brains recognize the different wavelengths of light as different colors.
Every type of atom or molecule produces radiation, or blocks radiation from other sources, only at particular wavelengths. Observations over the total array of wavelengths therefore provide a "cosmic fingerprint" that reveals the different varieties and numbers of atoms and molecules in the objects whose radiation we can study in detail. By measuring this fingerprint from any cosmic source of radiation, astronomers can also determine the motions within the source, as well as the speed with which the source is approaching or receding from us. Visible light, however, can furnish only a small portion of this fingerprint. On either side of the spectral region that contains light waves, vast domains of the electromagnetic spectrum extend to shorter and Radio Infrared Optical/Visible X ray Gamma ray longer wavelengths. Though human eyes cannot perceive this radiation, these domains are just as rich in information as the visible light with which we view our world. During past decades, astronomers have developed the tools to exploit most of these regions of the spectrum. Each new spectral domain opened by a new set of astronomical instruments not only has improved our understanding of objects already known, but also has revealed entire new classes of objects previously unsuspected. By studying cosmic sources of radio waves, for example, astronomers found totally unexpected phenomena such as pulsars, which produce rapid-fire bursts of radio emission; radio galaxies, in which explosive events accelerate charged particles to nearly the speed of light; and quasars, apparently the cores of young galaxies, where matter continuously spirals around and into a supermassive black hole.
Most radio waves, the longest-wavelength and lowest-frequency domain of the spectrum, can penetrate our atmosphere. But our atmospheric veil blocks most radiation outside the radio and visible-light domains, including gamma rays, x rays, ultraviolet light, and most infrared radiation. To improve our understanding of the cosmos, we require not only better ground-based observatories, which can detect visible light, radio waves, and some infrared radiation, but also space-borne observatories to study the cosmos in gamma rays, x rays, ultraviolet light, and those portions of the infrared spectrum that cannot penetrate Earth's atmosphere. By combining the results from these different instruments, we can understand sources of radiation far better than we could with observations made with any single telescope or within any particular domain of the spectrum.
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