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

Same as → nautical astronomy.

Navigational, adj. of navigation, from L. navigationem (nom. navigatio), from navigatus, p.p. of navigare "to sail, steer a ship," from navis "ship," cognate with Pers. nâv "ship," as below, + root of agere "to drive," → act; → astronomy.

Axtaršenâsi→ astronomy; nâvrâni "navigation," from nâv "ship;" O.Pers./Av. *nāv-, O.Pers. nāviyā- "fleet;" cf. Skt. nau-, nava- "ship, boat" + râni verbal noun of rândan "to drive, to cause to go," causative of raftan "to go, walk, proceed" (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").

Tide which occurs during the → first quarter and → third quarter of the → Moon when the pull of the Sun is at → right angles to that of the Moon.

Neap, from M.E. neep, from O.E. nepflod "neap tide" + → tide.

Kehkešan "small tide," from keh- "small, little," → low, + kešand, → tide.

Close; to a point or place not far away.

O.E. near "closer, nearer," comparative of neah, neh "nigh."

Nazdik, from Mid.Pers. nazdik "near," from nazd "close" (Mid.Pers. nazd, nazdik "near," nazdist "first;" O.Pers. ašna- "close;" Av. nazdišta- "nearest, next," nazdyo "nearer to," nas- "to come near, approach, reach;" cf. Skt. nédīyas- "closer, very close," nas- "to approach, to reach") + -ik, → -ic.

The longest wavelengths of the ultraviolet region, which are adjacent to the visible, from 200 to 350 nm.

→ near; → ultraviolet.

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; → asteroid.

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.

→ near; → earth; → object.

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.

→ near; → infrared.

1) A cloud of gas and dust in the interstellar space. There are three general types: → emission nebulae, → reflection nebulae, and → dark nebulae.
2) A celestial body appearing nebulous or fuzzy when seen with the telescope. Formerly, galaxies, which appeared nebular but are constituted of billions of stars, were not distinguished from truly nebular objects, made of gas and dust.

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.

→ nebula + → -ar.

The part of a nebular object's → spectrum that is created by → free-free emission.

→ nebular; → continuum.

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.

→ nebular; → hypothesis.

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 (→ [O III] doublet) and the ionized nitrogen doublet [N II] at 6548 and 6583 Å. See also → auroral line; → transauroral line.

→ nebular; → line.

A type of eruptive variable star, mainly young FU Orionis and T Tauri types, associated with nebulosity.

→ nebular; → variable.

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.
2) The state or condition of being nebulous.
3) A fuzzy celestial object, constituted of gas and dust, generally part of a larger → nebula.

→ nebulous; → -ity.

1) Hazy, vague, indistinct, or confused.
2) Cloudy or cloudlike.
3) Of or resembling a nebula or nebulae; nebular (Dictionary.com).

→ nebula; → -ous.

1) Being essential or indispensable.
2) Logic, Math.: A condition which must hold for a result to be true, but which does not guarantee it to be true. → if and only if.

M.E. necessaire, from L. necessarius "unavoidable," , from necesse "unavoidable, indispensable," from ne- "not," → un-, + cedere "to withdraw, go away, yield," → precession.

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.

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).

→ necessary; → and; → sufficient; → condition.

Logic: A → proposition if its → denial is self-contradictory. Also called "logical truth" and "non-contingent truth."

→ necessary; → truth.

1) The fact of being necessary or indispensable.
2) Something necessary or indispensable.

→ necessary; → -ity.