An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Plural form of → radius.

→ radius.

1) An apparatus for receiving or transmitting radio broadcasts.
2) Pertaining to the → radio waves of the → electromagnetic radiation.
3) As a prefix, indicating → radition or → radioactivity.

1); 2) Short from radiophone and radio-telegraphy.
3) Combining form of → radiation.

Râdio, loan from Fr., as above; partow→ ray.

A large number of narrow filaments in → radio continuum occurring toward the → Galactic Center, about 15 to 20 arc-minutes (some 50 parsecs in projection) north of → Sgr A*. The radio Arc is the prototype of → non-thermal filaments (NTFs) and resolves into a set of more than a dozen vertical filaments with lengths of about 30 pc distributed symmetrically with respect to the → Galactic equator (Yusef-Zadeh et al. 1984, Nature 310, 557). Among more than 100 NTFs found in the Galactic center region, the Arc is the only one known to show inverted spectrum with a → spectral index α = +0.3 (Law et al. 2008, ApJS 177, 515, and references therein). This implies a very hard energy spectrum of particles for a source of → synchrotron radiation.

→ radio; → arc.

The branch of astronomy that deals with the study of the Universe by means of → radio waves.

→ radio; → astronomy.

A burst of emission in the radio frequencies of the electromagnetic spectrum.

→ radio; → burst.

A → continuum emission with frequencies in the radio range of the electromagnetic spectrum.

→ radio; → continuum; → emission.

The representation in → radio wavelengths of an astronomical object that has emission in other parts of the → electromagnetic spectrum.

→ radio; → counterpart.

→ Electromagnetic radiation carried by → radio waves.

→ radio; → emission.

Total radiation in radio wavelengths going out from the 2π solid angles of a hemisphere. → flux.

→ radio; → flux.

The flux of → radio waves that falls on a → detector per → unit → surface area of the detector per unit → bandwidth of the radiation per unit → time. The unit is → jansky.

→ radio; → flux; → density.

The → electromagnetic radiation with the frequency range between 3 → kiloherz (kHz) to 300 → gigahertz (GHz). See also → radio wave.

→ radio; → frequency.

A galaxy that is extremely luminous at radio wavelengths between 10 MHz and 100 GHz. The radio luminosity of a strong radio galaxy (10³⁷-10³⁹ watts) can be up to a million times greater than the radio output of an ordinary galaxy and up to a hundred times greater than the optical luminosity of a galaxy such as the Milky Way. The optical counterparts of radio galaxies are usually an → elliptical galaxy. Radio galaxies often exhibit jet structure from a compact nucleus. They typically display two → radio lobes that are often approximately aligned with the jets observed in the optical and that may extend for millions of → light-years.

→ radio; → galaxy.

An → interferometer designed for radio frequencies.

→ radio; → interferometer.

An → astrophysical jet appearing in the radio wavelengths of the electromagnetic spectrum.

→ radio; → jet.

An extended region of diffuse radio emission, often dumbbell shaped, that surrounds a radio galaxy.

→ radio; → lobe.

The electromagnetic noise at radio wavelengths.

→ radio + → noise.

A → pulsar that emits → pulses in → radio waves. The bulk of discovered pulsars are radio pulsars. There is a small number of pulsars that emit at optical wavelengths, X-ray wavelengths, and gamma-ray wavelengths.

→ radio; → pulsar.

A → recombination line whose wavelength lies in the radio range of the electromagnetic spectrum. Radio recombination lines are the result of electronic transitions between high energy levels (n > 50) in an atom or ion.

→ radio; → recombination line.

A signal in the → radio frequency region of the → electromagnetic spectrum.

→ radio; → signal.

A condition in which all fixed or mobile equipments capable of radio transmitting in an area are kept inoperative, typically for the duration of some sensitive time period. The term has both military and civilian applications.

→ radio; → silence.