Basic Information Glossary
Radio Astronomy Glossary
Many people feel that astronomers speak their own language. Consider this glossary your
"Scientist-to-Teacher" translation dictionary.
- Angstrom
- An angstrom is a unit of length that is equivalent to 10^-10m or 0.1nm. Used mainly to specify the wavelength of radiation.
- Azimuth
- The angular distance of an object, measured eastward, from north. 0° is due north,
90° is due east, 180° is due south, and 270° is due west.
- Black Body Radiation
- The thermal radiation that would be emitted from a black body (an object that reflects no incoming
radiation) at a particular temperature.
- Corona
- The outermost part of the sun's atmosphere.
- Coronal Mass Ejection
- The ejection of a large amount of material from the Sun. Also refered to as a CME. "As if the Sun lets loose a big burp!" - Dr. P. Erickson
- Declination
- The angular distance of an object north or south of the celestial equator.
- Doppler Effect
- The compression or expansion of a wave due to its motions towards you or away from you.
- Electromagnetic Wave
- A wave generated by an electromagnetic field. These waves (unlike sound waves) do NOT require a medium to travel through.
Go to The Electromagnetic Spectrum (by Georgia State University)
for a chart of the electromagnetic spectrum and a wavelength/frequency calculator.
- Elevation
- The angular distance of an object above the horizon. 0° is on the horizon and 90° is straight up.
- Electron
- A tiny particle that has a negative charge
- Emission
- The release of a photon from an atom when an electron in the atoms jumps from a higher to a lower energy level.
- Excitation
- When an atom absorbs a photon and is raised to a higher energy level.
- Focal Length
- The distance between the center of a reflecting surface (or refracting medium) and the focal point.
- Focal Point
- The point where parallel beams are brought together (into focus) by a convex lens
or a concave mirror (or other reflecting surface.)
- Interference
- Unwanted radio signals received by a radio telescope that originate in human activity rather than natural phenomena.
- Ion
- An atom or molecule that has lost or gained one or more electrons, and is now positively or negatively charged.
- Ionosphere
- An upper level of the atmosphere where ions and electrons can be separated.
- Light Year
- The distance traveled by light, or other electromagnetic radiation,in one tropical year through space. One light year is equivalent to 9.4607 x 10^12 km, or 63,240 astronomical units, or 0.3066 parsecs.
- Maser
- A small celestial source of electromagnetic radiation in the microwave range. They have been detected
in the atmospheres of old variable stars and molecular clouds associated with newly formed
or forming stars.
- Nebula
- A cloud of interstellar gas and dust.
- Noise
- Unwanted fluctuations that occur in the output of any electronic device. It can be associated
with background radiation and thermal radiation from your instrument.
- Optical Depth
- A measure of the absorption of radiation as it passes through a medium. Essentially, it is how far light can penetrate a material. For example, dirty, muddy water has a shorter
optical depth than clear water.
- Parsec (pc)
- A astronomical distance approximately 3.3 light years. The term parsec comes from a parallax second, since a parsec is defined by the parallax of object as seen from opposite ends
of the Earth's orbit.
- Plasma
- The high- energy state of matter when electrons are ripped from molecules, leaving a mixture of the
negatively charged electrons and the positively charged ions. It is formed at high temperatures.
- Radar
- A device that bounces radio transmissions off of objects and studies the reflections.
- Radiation
- Energy propogating in the form of electromagnetic waves or photons.
- Radio astronomy
- The study of the Universe in the radio part of the electromagnetic spectrum. The radio spectrum ranges from approximately 1mm to 30 meters, almost all of it accessible from ground-based observatores, day and night.
- Radio Telescope
- A telescope that receives radio emissions from celestial bodies. The key difference between radars and
radio telescopes is that radars actively probe an object by emitted radio waves and a radio telescope passively
receives radio waves.
- Right Ascension (RA)
- The angular distance of an object measured eastwards along the celestial equator.
- Solar Wind
- The flow of energetic charged particles from the sun's corona.
- Sun Spot
- Relatively dark spots on the sun. They are the centers of intense, localized magnetic fields.
- Thermal Line
- A known radio emission line.
- Variable Star
- A star whose physical properties (brightness, radial velocity, and spectral type) vary with time.
- Wavelength
- The distance between successive peaks or troughs of a wave. Wavelengths are equal to the speed of the wave divided by its frequency.
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