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

Noise in radio wavelengths caused by natural atmospheric processes, mainly lightening discharges in thunderstorms. They can affect radio observations.

→ atmospheric; → noise.

An unwanted signal in a system which is producing or recording a signal. For instance, a randomly fluctuating signal superimposed on the signal from a cosmic radio source.

→ background; → noise.

Radio waves emanating from extraterrestrial sources.

→ cosmic; → radio; → noise.

In a → CCD detector, statistical fluctuation of the → dark current, equal to the square root of the dark current. CCDs can be cooled either with thermoelectric coolers or liquid nitrogen to reduce this effect. Ideally, the dark current noise should be reduced to a point where its contribution is negligible over a typical exposure time.

→ dark; → current; → noise.

A diffuse radio signal that originates outside the solar system. It is strongest in the direction of the Galactic plane.

→ galactic; → radio; → noise.

The random fluctuation of voltage across a resistor caused by the thermal excitation of electrons within it, and the dissipation of power associated with these fluctuations. More generally, an intrinsic noise generated by thermal agitation of electrons by all bodies whose temperature is above 0 K. Also called → thermal noise, Johnson noise, or Nyquist noise.

Named after John Bertrand Johnson (1887-1970) and Harry Nyquist (1889-1976) Swedish-born American engineers and physicists, who did important work on thermal noise and information theory. → noise.

1) The → random → fluctuations that are always associated with a measurement that is repeated many times over. Any unwanted disturbance, random or → systematic, which contaminates the → signal from an object under study. More specifically:
2) Electronics: An undesired signal within the useful frequency band.
3) Acoustics: Any extraneous sound tending to interfere with the perception of wanted sound.
See also:
→ atmospheric noise, → background noise, → cosmic radio noise, → dark current noise, → Galactic radio noise, → Johnson-Nyquist noise, → noise source, → noise temperature, → noise voltage, → noise-equivalent power, → photon noise, → quantum noise, → radio noise, → random noise, → readout noise, → receiver noise, → Schottky noise, → shot noise, → signal-to-noise ratio, → speckle noise, → stationary noise, → system noise, → thermal noise, → white noise.

Noise, of obscure origin; it has been related to O.Fr. noise "uproar, brawl," apparently from L. nausea "disgust, annoyance," literally "seasickness." Alternatively the O.Fr. word is traced to L. noxia "hurting, injury, damage."

Nufé "noise," related to Mod.Pers. noyidan "to cry loud, lament," navidan, nâvidan "to lament," noyé, nôyah "plaint, mown," navâ "sound, song," (with prefix *uz-) zenudan, zenav-, zonudan "to wail," Ossetic niwyn/newun "to howl," O.Khotanese nuva- "to make a noise," Yaqnâvi nuyok "crying, howling," novva "sound," Shahmirzâdi nâv- "to cry; cf. Skt. nav- "to sound loudly, roar," náva- "show of joy or triumph;" L. nuntius "messenger," adnuntiare "to annoince;" Tocharian AB nu- "to roar, PIE *neu- "to shout".

An electronic device designed to generate known amounts of radio noise in order to test and calibrate the receivers of radio telescopes.

→ noise; → source.

A means for specifying the noise generated as unwanted → electromagnetic radiation in a receiver system or one of its components. It is usually measured in terms of the equivalent temperature in a → Rayleigh-Jeans spectrum. Noise temperature is used mainly in radio astronomy.

→ noise; → temperature.

Fluctuations of electric potential in a physical system due to spontaneous disturbances in the system.

→ noise; → voltage.

A measure of the sensitivity of an electronic detector, defined as the power input to the detector that will create a signal to noise ratio of one for an integration time of half a second.

→ noise; → equivalent; → power.

An intrinsic noise caused by the quantum nature of light. Same as → quantum noise.

→ photon; → noise.

A random variation of signal due to fluctuations in the average rate of incidence of quanta on a detector. Quantum noise is described by the → Poisson distribution. Same as → photon noise and → shot effect.

→ quantum; → noise.

The electromagnetic noise at radio wavelengths.

→ radio + → noise.

Unpredictable noise comprising large numbers of frequent, transient impulses occurring at statistically random time intervals. Thermal noise is a form of random noise.

→ random; → noise.

The noise added in the process of reading a detector such as a CCD.

→ reading rate; → noise.

The unwanted signal affecting a receiver.

→ receiver; → noise.

Excess voltage generated by random fluctuations in the emission of electrons from a hot cathode, causing a hissing or sputtering sound (shot noise) in an audio amplifier and causing snow on a television screen. Same as → shot effect, → shot noise.

Named after Walter Hans Schottky (1886-1976), German physicist; → noise.

Same as → Schottky noise and → shot effect.

→ shot effect.

→ Schottky noise.

Concept used to quantify the effects of noise. It is the ratio of a signal to the standard deviation of the signal.

→ signal; → noise; → ratio.