What is Radio Astronomy?
Astronomers Study all Forms of Celestial Electromagnetic Waves
May 22, 2008
Traditionally astronomers studied stars, planets, galaxies, and other celestial objects using visible light and optical telescopes. Visible light is simply the range of electromagnetic radiation that the human eye can detect. There is nothing astronomically special about visible light compared to other forms of electromagnetic waves.
By the middle of the twentieth century the technology to detect other types of electromagnetic waves became available. Astronomers also began to realize that these other wavelength ranges of electromagnetic waves could help us probe the universe.
Origin of Radio Astronomy
In the 1930s, Karl Jansky discovered the first extraterrestrial radio signals. These signals originated from the center of the Milky Way galaxy. Jansky's discovery launched the field of radio astronomy, so he is considered the father of radio astronomy.
Radio Astronomy
Just as optical astronomers study the visible light from celestial objects, radio astronomers study the radio waves from planets, stars, galaxies, and other celestial objects. Radio telescopes use radio receivers with antennas that can point in a specific direction, so astronomers can study the radio waves from a specific celestial object.
Optical reflecting telescopes use a concave mirror and a smaller secondary mirror to focus incoming light into an eyepiece, camera, or other light detector for detailed study. Radio telescopes use similar principles but with radio waves.
Radio telescopes use a large concave reflector. This reflector is metal and is designed to reflect radio waves. It is somewhat like a large version of an antenna for satellite television signals. These reflectors must be steerable, so they can point towards any direction of the sky. They also have a relatively narrow field of view, so they can select the radio waves from a specific celestial object. The large size increases their sensitivity to allow astronomers to study faint radio sources.
At the focal point of this reflecting antenna a radio receiver picks up the celestial radio waves. A tunable receiver allows astronomers to study specific frequency radio waves. Astronomers can map a region of the sky at a specific radio frequency. They can also study the radio spectrum of a specific celestial object, whose signal strength varies with the frequency.
Discoveries from Radio Astronomy
Radio waves have a longer wavelength than visible light. Interstellar dust grains that would be large enough to completely block a visible light wave are often too small to affect radio waves. For this reason radio waves can probe dusty regions of interstellar space that block visible light.
There is a lot of interstellar dust in the plane of the Milky Way galaxy, so mapping the spiral structure of our galaxy is easier with radio astronomy than with optical astronomy.
Newly forming stars are usually still enshrouded in dust. Radio astronomy helps us probe these dusty regions to study star formation. Stars usually form in molecular clouds which astronomers study with radio telescopes.
Pulsars, which are rapidly rotating neutron stars, were first discovered at radio wavelengths. They are brightest at radio wavelengths, so radio astronomers still gather much of our knowledge of these objects.
Quasars and other very energetic active galaxies are also brightest at radio wavelengths. Radio astronomers help us understand these highly energetic objects.
Further Reading
Zeilik, M. Astronomy: The Evolving Universe, 9th ed. Cambridge, 2002.
Chaisson, E. and McMillan, S. Astronomy Today, 5th ed. Pearson Prentice Hall, 2005.
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