near-Earth asteroid (NEA)
Fr.: astéroïde géocroiseur
An → asteroid whose orbit lies partly between 0.983 and 1.3 → astronomical units from the Sun, so that it passes close to the Earth. Currently thousands of near-Earth asteroids are known, ranging in size up to about 30 km. Among them, there are between 500 and 1,000 such asteroids larger than one km in diameter. They are divided into three subclasses: → Amor asteroids, → Apollo asteroids, and → Aten asteroids. See also → near-Earth object.
near-Earth object (NEO)
An → asteroid, → comet, or large → meteoroid whose orbit brings it exceptionally close to the Earth, and which may therefore pose a collision danger. Most such objects are in orbits around the Sun with → perihelion distance less than 1.3 → astronomical units. See also → near-Earth asteroid.
forusorx-e nazdik (#)
Fr.: proche infrarouge
That region of the → electromagnetic spectrum covering shorter infrared wavelengths. It contains the → infrared windows between about 0.8 and 8 → microns, but the longer wavelength limit is not well defined. See also: → infrared radiation, → mid-infrared, → far-infrared, → submillimeter radiation.
1) A cloud of gas and dust in the interstellar space. There are three
general types: → emission nebulae,
→ reflection nebulae,
and → dark nebulae.
From L. nebula "mist," nimbus "rainstorm, rain cloud;" cognate with Av. napta- "moist," nabās-câ- "cloud," nabah- "sky;" Pers. nam "moisture;" cf. Gk. nephos "cloud, mass of clouds," nephele "cloud;" Skt. nábhas- "moisture, cloud, mist;" O.H.G. nebul; Ger. Nebel "fog;" O.E. nifol "dark;" PIE base *nebh- "cloud, vapor, fog, moist, sky."
Miq "nebula" (used by Tusi, in Pers. translation of Sufi's "Book of Fixed Stars"), variants meh "fog," mož, Tabari miyâ, Lori/Laki (kara) mozy, Ossetic mig/megæ, from Mid.Pers. mēq "cloud, mist;" Av. mēγa- "cloud;" cf. Skt. meghá- "cloud, overcast weather;" Gk. omikhle "mist;" Lith. miglà "mist, haze;" PIE base *mighlā- "cloud."
Of or relating to or resembling a → nebula.
Fr.: continuum nébulaire
Fr.: hypothèse nébulaire
The hypothesis first put forward in the 18-th century that the solar system formed from a primeval nebula around the Sun. Same as the → Kant-Laplace hypothesis.
Fr.: raie nébulaire
A → forbidden line that is found in the spectra of → interstellar → ionized gas. The nebular lines are emitted by several atomic species (e.g. O, O+, O++, N+, S++) and correspond to the → transition from the electronic → metastable state 1D to the → ground state 3P. Examples are the doubly ionized oxygen lines [O III] at 4959 and 5007 Å. See also → auroral line; → transauroral line.
Fr.: variable nébulaire
A type of eruptive variable star, mainly young FU Orionis and T Tauri types, associated with nebulosity.
A hypothetical element, the existence of which was postulated in the nineteenth century to account for unidentified emission lines (e.g. at 3727 and 5007 Å) in the spectra of some luminous nebulae. It was also believed that this element had a small atomic weight. However, the advances of chemistry and physics showed that all the light elements were known and there was no place for this elusive element. Those unidentified lines have now been shown to come from known elements, but they are not usually observable under laboratory conditions. → forbidden lines.
From nebul(a), → nebula, + -ium L. neuter suffix.
1) A nebulous form, shape, or mass.
1) Hazy, vague, indistinct, or confused.
1) Being essential or indispensable.
Bâyesté, p.p. of bây-, bâyestan "to be necessary," from Mid.Pers. abây-, abâyistan "to be necessary" (abâyišn "necessity," abâyišnig "necessary"), from Proto-Ir. *upa-aya- "to reach," from upa-, → hypo-, + ay- "to go, to come," → precession.
necessary and sufficient conditions
butârhâ-ye bâyesté o basandé
Fr.: conditions nécessaire et suffisante
If event A must occur for event B to occur, then it is said that A is → necessary for B. If event A may cause B but there could be some other cause as well, then it is said that A is sufficient to cause B. See also → if and only if (iff).
Fr.: vérité nécessaire
1) The fact of being necessary or indispensable.
A slender pointed piece of metal, usually steel. → magnetic needle.
M.E. nedle, O.E. naeðlæ, nedlæ (cf. O.S. nathla, O.N. nal, O.Fris. nedle, O.H.G. nadala, Ger. Nadel); PIE root *(s)ne- "to sew, to spin;" cf. Skt. snayati "wraps up;" Gk. nein "to spin;" L. nere "to spin."
Suzan, Mid.Pers. sôzan, sucan, related to sok "pointed stick for driving cattle;" Av. sūkā- "needle;" cf. Skt. sūcī- "sting;" L. cuneus "wedge;" PIE base kū- "sharp; spike."
To deny the existence or truth of. To cause to be ineffective or invalid.
From L. negatus p.p. of negare "to say 'no', deny," from Old L. nec "not," from PIE base *ne- "no, not."
Nâyidan infinitive from nâ "no, not," variants na, ni, ma- (prohitive); from Mid.Pers. nê, ma "no, not;" O.Pers. naiy, nai "not;" Av. nôit, naē "not;" cf. Skt. ná "not;" cf. L. ne-, in-, un-; Gk. ni; Lith. nè; O.C.S. ne "not;" PIE *ne-, as above.
1) The act of denying; → denial.
Verbal noun of → negate.
Expressing, containing, or consisting of a negation, refusal, or denial.
From O.Fr. negatif (fem. negative), from L. negativus, "denying, inhibiting (legal actions); denied/refused; negative," from negare "to refuse, say 'no'" from Old L. nec "not", from Italic base *nek- "not," from PIE base *ne- "no, not."
Nâyidâr, from nâyidan, → negate, on the model of xaridâr, foruxtâr, xâstâr, virâstâr, etc.