Overview (The Solar System)
Until radio experiments by Karl Guthe Jansky (1905-1950) in the 1930’s, virtually all astronomical knowledge was a product of analyzing visible starlight. Historically, optical telescopes and photographic techniques enhanced scientists’ vision of the small range of frequencies in the Electromagnetic spectrum perceived as visible light (400 to 700 nanometers in wavelength). Radio signals are found in the long-wavelength part of the electromagnetic spectrum, ranging from millimeters to several thousand meters. Jansky’s 1932 discovery of radio sources beyond Earth ultimately led astronomers to imagine millions of discrete radio transmitters broadcasting throughout the universe. The small slit of visible light through which astronomers had previously viewed the cosmos suddenly expanded to a wide-open window with the addition of radio signals. Unfortunately, the radio universe is invisible to humans’ biological eyes, and consequently it is necessary to convert radio signals into a visual format for interpretation of data.
A radio telescope collects and converts radio signals through its basic components: the antenna, which collects the signals; an amplifier, which magnifies these incredibly weak waves; and a recorder, which translates this information into a medium that can be viewed. A Radio telescope is a directional antenna that may take several forms. Jansky’s design was a square wooden frame around which he wrapped wire....
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Applications (The Solar System)
The universe, before the introduction of radio astronomy, appeared rather stable if not static apart from the occasional supernova. Then, with the development of radio and the associated radio telescope in the early twentieth century, a new picture emerged of an active universe. Discovery of radio sources identified as pulsars underlies this dynamic element.
In 1934, two astronomers, Walter Baade and Fritz Zwicky, proposed that the remaining Stellar core from a supernova explosion represents the transition of a star to a neutron star. This theory received little attention until 1967.
In the mid-1960’s in Cambridge, England, Antony Hewish and his colleagues were building a radio telescope to observe scintillation, or twinkling, of radio sources known as quasars. By coincidence, the parameters for the telescope matched the characteristics of pulsars (later to be described as rapidly rotating Neutron stars). Jocelyn Bell, a graduate student, detected a regular pulsating source of radio emissions that kept appearing from the same area in the sky and with a regularity of every 1.33 seconds. Bell’s discovery of pulsars was the beginning of a small Revolution in astronomy. Their signals were unlike any previously detected from stars or galaxies. The intriguing idea of the Little Green Men (LGM) phenomenon was entertained for a brief time. Then another Pulsar was discovered, which was pulsating at 1.2 seconds. It was the...
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Context (The Solar System)
The ability to see the universe through the radio window is a fairly recent technological development, whose evolution parallels the maturation of radio and its associated technology. Transmission of radio waves through space was demonstrated in 1887 by German physicist Heinrich Rudolph Hertz (1857-1894) in experiments based on predictions of James Clerk Maxwell (1831-1879). This successful demonstration began the age of radio.
Some astronomers suspected that stars might be a source of radio waves; the most easily examined star of course is the Sun. The search for solar radio signals began in 1890 with American inventor Thomas Alva Edison (1847-1931), followed in England by Sir Oliver Joseph Lodge (1851-1940) in 1894 and Charles Nordman of France in 1900. Negative results from their experiments diminished interest in this line of research. The idea of extraterrestrial radio waves generally receded from the minds of the astronomical community at this point. Scientists of the period were not aware of the ionized reflecting layer in the upper atmosphere (ionosphere), which effectively filters radio frequencies longer than about 20 meters.
This apparent failure of radio science did not deter its technological development. Radio caught the imagination of the public and scientists with Guglielmo Marconi’s (1875-1937) transatlantic transmission in 1901. This achievement led Arthur Edwin Kennelly (1861-1939) and Oliver Heaviside...
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Further Reading (The Solar System)
Burke, Bernard F., and Francis Graham-Smith. An Introduction to Radio Astronomy. Cambridge, England: Cambridge University Press, 2002. A review of radio observations of stars, pulsars, quasars, radio galaxies, and the center of the Milky Way, including a detailed explanation of the cosmic microwave background. Technical.
Condon, J. J., and S. M. Ransom. Essential Radio Astronomy. Available online at http://www .cv.nrao.edu/course/astro534. Detailed notes from a National Radio Astronomy Observatory/University of Virginia course in radio astronomy. Includes links to chapters on pulsar physics and observations.
Hey, J. S. The Evolution of Radio Astronomy. New York: Science History Publications, 1973. A fine historical account of an emerging science from one of its pioneers.
Jansky, Karl G. “Electrical Disturbances Apparently of Extraterrestrial Origin.” Proceedings of the Institute of Radio Engineers 21 (1933): 1387-1398. This paper is the primary source for radio astronomy and one of the most important for astronomy as a whole. Jansky describes many basic astronomical concepts as well as his announcement of an extraterrestrial source. Readable and informative.
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...
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Radio Astronomy (Encyclopedia of Science)
Matter in the universe emits radiation (energy) from all parts of the electromagnetic spectrum, 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.
Radio astronomy is the study of celestial objects by means of the radio waves they emit. Radio waves are the longest form of electromagnetic radiation. Some of these waves measure up to 6 miles (more than 9 kilometers) from peak to peak. Objects that appear very dim or are invisible to our eye may have very strong radio waves.
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