Radio astronomy has its roots back in the 1930's when Karl Jansky accidentally detected radio emission from the center of the Milky Way as part of his research on the interference on transatlantic phone lines. The British advanced radio antenna technology in their development of radar technology to fight the German warplanes in World War II. After the war, astronomers adapted the technology to detect radio waves coming from space.
A radio telescope uses a large metal dish or wire mesh, usually
parabolic-shaped,
to reflect the radio waves to an antenna above the dish. An example of a
mesh is shown at
left. This was the mesh of the parabolic dish for the former 100-meter
radio telescope at
Green Bank, West Virginia (photos courtesy of
National Radio
Astronomy Observatory). Looking from
underneath the radio
telescope, a person could see the clouds in the sky overhead but to
the much longer
wavelength radio waves, the metal mesh was an excellent reflector.
The signal from the antenna is sent to an amplifier to magnify the very faint signals. At the last step, the amplified signal is processed by a computer to turn the radio signals into an image that follows the shape of the radio emission. False colors are used to indicate the intensity of the radio emission at different locations. An example is shown below for Jupiter. Charged particles in its magnetic field produce a large amount of radio energy in donut-shaped regions around its center. A visible band image of Jupiter is shown below the radio image.
Radio telescopes are much larger than optical telescopes because radio wavelengths are much longer than optical wavelengths. The longer wavelengths means that the radio waves have lower energy than optical light waves. In order to collect enough radio photons to detect a signal, the radio dishes must be very large. Both optical and radio telescope reflectors use a parabolic shape to perfectly focus the light to a point. Increasing the size of the radio dish is also necessary in order to improve the clarity of the radio images. I will discuss the issue of image clarity further in the next two sections.
Radio telescopes detect the emission from cool clouds of hydrogen in the space between the stars. Hydrogen atoms are the most common type of atoms in the universe and much of the hydrogen gas is too far away from any star to produce emission in the optical wavelength band. Therefore, radio telescopes are a vital tool in understanding the universe. I will discuss further the use of radio waves to explore the material between the stars and the structure of our galaxy in the interstellar medium chapter.
Go back to previous section --
Go to next section
last updated: 28 May 2001