Introduction to Science in the Galactic Plane
Lesson 7:The Radio Telescope
QUESTION: What is a Radio Telescope?
Radio telescopes collect radio waves from astronomical sources, such as
Supernovas, Star forming regions, pulsars, black holes at the centers
of distant galaxies, and the background emission from the Big Bang.
Radio telescopes work in a similar manner to optical telescopes, by collecting
radio wavelength light and focusing it on the detector. For optical
telescopes, the detectors are your eye, photographic film or a CCD camera.
For radio telescopes, the receiver is the combination of a feed antenna,
amplifiers and a power detector. Radio telescopes measure the
power from the radio sources as a function of position around the
source and as a function of radio wavelength to make a spectrum.
The Galactic Plane A (GPA) survey uses the 45 foot (13.6 meter) diameter
radio telescope in Green Bank, West Virginia to map the Milky Way Galaxy.
In this lesson, the student is shown how a radio telescope collects
radio waves and focuses them on the receiver.
Galactic Plane Science
The Perfect Shape: A Parabola
Most large Radio and Optical telescopes have large parabolic
surfaces (mirrors) which focus the radio and light waves onto a detector.
The large surface is needed to collect the very faint signals for
detection by a receiver.
The sensitivity of a radio telescope increases linearly with the
surface area of the primary reflector.
A simple formula relates the resolution of the telescope to
its size, measured in WAVE-LENGHTs.
The angular resolution, THETA,
of the telescope increases linearly with the DIAMETER of the
telescope. Smaller resolution (smaller THETA) means
that smaller structures can be seen (smaller is better).
THETA = 1.2 * WAVE-LENGTHS / DIAMETER
Where the THETA is measured in RADIANS. To convert from
RADIANS to DEGREES, multiply by 57.3.