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

The highest clouds in the Earth's atmosphere, at altitudes between 75 and 90 km. They resemble thin cirrus clouds with a bluish or silverish color, and are visible only during twilight.

From nocti- combining form of L. nox, → night, + L. lucent p.p. of lucere "to shine," from lux→ light; → cloud.

Abr, → cloud, + šabtâb "noctilucent," from šab, → night, + tâb present stem of tâbidan "to shine," → luminous.

Relating to or of the nature of a node.

→ node; → -al.

The line connecting the ascending and descending nodes of an orbit.

→ nodal; → line.

Any of the two points on the → axis of a → lens system, such that if the → incident ray passes through one, travelling in a given direction, the → emergent ray passes the other in a parallel direction.

→ nodal; → point.

For a ring inclined to the planet's equator, the points at which the ring crosses the equator (nodes) slowly move around the planet (regress) in a direction opposite to that of the ring's orbital motion. (Ellis et al., 2007, Planetary Ring Systems, Springer).

→ nodal; → regression.

1) A point of zero → amplitude in a system of → stationary waves. See also → antinode.
2) A → junction point in a network.
3) Same as → orbital node; see also → lunar node.
4) In → graph theory, same as → vertex.

From L. nodus "knot;" cognate with necto "I bind," Skt. nahyati "binds, ties," Av. naska-, "bundle," Old Irish nascim "to bind," Old Norse knutr, Norwegian knut, Icelandic hnutur, O.E. cnotta, Modern E. knot, O.H.G. knotto, Ger. Knoten; PIE root *ned- "to bind, tie."

Gereh "knot," from Mid.Pers. grih "knot;" Sogdian γr'nš "knot, bond, joining;" Khotanese grantha- "knot;" cf. Skt. granthi- "knot."

The time interval between two successive passages of the Moon through its ascending node (27.212220 days, i.e., 27 days 5 hours 5 minutes 35.8 seconds). Nodical month is important for predicting eclipses. Also called → draconic month.

Nodical adj. of → node; → month.

Mâh, → month; gerehi, adj. of gereh, → node; gowzahri→ draconic month.

1) A small node, knot, or knob.
2) A small, rounded mass or lump.

From L. nodulus "small knot;" → node, → -ule.

Gerhule, from gereh, → node, + -ul, → -ule.

A → symmetry in a physical system leads to a → conserved quantity. For example, symmetry under → translation corresponds to conservation of → momentum, symmetry under → rotation to conservation of → angular momentum, and symmetry in → time to conservation of → energy. The Noether symmetry theorem is a fundamental tool of modern theoretical physics and the calculus of variations, allowing to derive conserved quantities from the existence of variational symmetries.

Named in honor of the German-American woman mathematician Amalie Emmy Noether (1182-1935), who published the theorem in 1918 ("Invariante Variationsprobleme," Nachr. D. König. Gesellsch. D. Wiss. Zu Göttingen, Math-phys. Klasse 1918: 235-257).

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.

A set or system of names or terms assigned to objects or items in a particular science or art.

From Fr. nomenclature, from L. nomenclatura "calling of names," from nomenclator, variant of nomenculator "one who announces names, namer," from nomen, → name, + calator "caller," from calare "to call."

Nâmgozâri, from nâm, → name, + gozâri, verbal noun of gozâštan "to place, put; to allow, let," related to gozaštan "to pass, proceed, go over;" Mid.Pers. vitar- "to let pass, lead; to pass;" O.Pers. vitar- "to go across," viytarrayam "I put across;" Av. tar- "to cross over," vī-tərəta- "taken away, isolated;" ultimately Proto-Ir. *ui-tar-.

1) Of, pertaining to, or constituting a name or names, a noun or nouns.
2) Describing a value quoted for commodity, expectation, or its current estimate, as opposed to the actual value. → nominal value.
3) Within acceptable limits; as expected.
4) a) Grammar: Relating to a noun or to any word or word group that functions as a noun. b) A word which differs from a noun but functions as one.

From L. nominalis "pertaining to a name or names," from nomen "name," cognate with Pers. nâm, as below.

Nâmenâl, from nâmen, from O.Pers./Av.nâman-, → name, + suffix -al.

An approximate value of the → focal length, used for the classification of lenses, mirrors, or cameras, as opposed to the measured one.

→ nominal; → focal; → length.

The assigned, specified, or intended value of a quantity.

→ nominal; → value.

1) To propose (someone) for appointment or election to an office; to appoint to a duty or office.
2) To name; designate.

From L. nominatus, p.p. of nominare "to name, call by name, give a name to," also "name for office," from nomen, → name.

Nâmenidan, from nâmen, from O.Pers./Av.nâman-, → name, + infinitive suffix -idan.

Having received a → nomination.

Past participle of → nominate.