A body that absorbs all the radiation falling on it. It has no reflecting power. It is also a perfect emitter of radiation. The concept of a blackbody is hypothetical. However, the radiation from stars can be described by assuming that they are black bodies. Black-body radiation is the thermal radiation that would be emitted by a black body at a particular temperature.

Cyclotron Maser Instability (from Planetary Radio Emissions by Donald A. Gurnett in the Astronomy and Astrophysics Encylopedia,1992, pg 536)

Five planets, Earth, Jupiter, Saturn, Uranus, and Neptune, produce powerful radio emissions via a mechanism known as the cyclotron maser instability. These intense radio emissions from the five planets have several common characteristics:

These characteristics are all consistent with a plasma instability called the cyclotron maser instability. For this instability an electromagnetic wave acts to organize the phase of the cyclotron motion in such a way that the electrons radiate in phase with the original wave


The lower part of the Sun's outer atmosphere that lies directly above the Sun's visible surface (photosphere)

Dynamic Spectra

A plot of the intensity of a signal as a function of frequency and time

Electromagnetic radiation

A flow of energy that is produced when electrical charged bodies, such as electrons, are accelerated.

Io Phase

The orbital position of Io can be defined by something called the Io phase. The Io phase is 0 degrees when Io is directly behind Jupiter as seen from Earth. The Io phase increases as Io orbits until it becomes 180 degrees when Io crosses in front of Jupiter as seen from Earth.

Io Plasma Torus

The Io plasma torus is a ring of plasma surrounding Jupiter near the orbit of Jupiter's moon Io. The plasma consists mostly of oxygen and sulfur ions which originate from Io and are caught up in Jupiter's magnetic field. As the magnetic field rotates with Jupiter it sweeps the plasma into a torus around Jupiter. The ions emit radiation mostly in the extreme ultraviolet, but some emissions are observable by earth-based telescopes.

Jovian Decimetric and Decametric Radio Emission

Jupiter not only emits thermal radiation but also non-thermal radiation in two frequency bands: Decimetric radiation between 1000 and 3000 MHz and the decametric radiation between 5 and 40 MHz. Radiation below 5MHz is absorbed by the Earth's atmosphere and cannot be absorbed on the ground.

Jovian central meridian longitude (CML)

CML is defined by the longitude of Jupiter facing the Earth at a certain time.

Modulation lanes

A spectral feature present in the dynamic spectra of the Jovian decametric radio emission. Modulation lanes were reported by J. Riihimaa in 1968. They consist of drifting curved structures

Non-thermal radiation

Electromagnetic radiation, such as synchrotron emission, that is produced by the acceleration of electrons or other charged particles but is non-thermal in origin, i.e. its spectrum is not that of a perfect black-body radiator.


A measure of the way in which light or other electromagnetic radiation from a celestial body is affected by factors such as scattering due to cosmic dust or strong stellar or interstellar magnetic fields, or reflection from a surface. It can also be described as the degree to which the direction of the electric or magnetic vector in an electromagnetic wave changes in a regular fashion. Waves in which the electric vectors are entirely vertical or horizontal with respect to the direction of motion are described plane or linearly polarized. In general, both polarizations are present and the wave is then elliptically polarized in the right handed or left-handed sense accordingly as the resultant vector rotates clockwise or anticlockwise when viewed along the direction of motion of the wave.

Radio Spectrograph

An instrument used in radio astronomy for obtaining the intensity of the emission as a function of frequency.

Solar Bursts (Type III)

The Type III bursts are short, strong bursts that begin right after a visible flare and move rapidly from around 500MHz to lower frequencies. At low frequencies (less than 25 MHz) the drift is very slow. The bursts display a slow negative drift rate of 1MHz/sec.  These bursts are caused by solar flares which eject high energy electrons into space zipping away from the sun at about 1/4 the speed of light. These electrons excite radio waves in space as they move along in the Sun's outer atmosphere. Since the density of the plasma in space falls off as you move away from the sun, these zipping electrons cause radio emission at successively lower frequencies. 

Synchrotron  radiation

Electromagnetic radiation from very high energy electrons moving in a magnetic field. It is an example of non-thermal emission.

Thermal Radiation

Electromagnetic radiation resulting from interactions between electrons and atoms or molecules in a hot dense medium.