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

In evolutionary models of → low-mass and → intermediate-mass stars, the occurrence of a → helium shell flash on the → horizontal branch of the → post-AGB track, while → hydrogen shell burning is still going on.

→ late; → thermal; → pulse.

In the → Hubble classification, a galaxy on the left part of the → Hubble sequence. See also → early-type galaxy.

→ late; → type; → galaxy.

A star of → spectral type K, M, S, or C, with a surface temperature lower than that of the Sun. → early-type star. See also → spectral classification.

→ late; → type; → star.

Present but not visible, apparent, or actualized; existing as potential (Dictionary.com). → latent heat.

From L. latentem (nominative latens), pr.p. of latere "to lie hidden."

Nahân "concealed, hid; clandestine;" Mid.Pers. nihân "secrecy, a secret place, a hiding place," nihânik "concealed;" Av. niδāti- "deposing, deposit."

The amount of → thermal energy that is absorbed or released by a unit amount of a substance in the process of a phase change under conditions of constant pressure and temperature.

→ latent; → heat.

Of or relating to the side; situated at, proceeding from, or directed to a side (Dictionary.com).

M.E., from O.Fr. latéral and directly from L. lateralis "belonging to the side," from latus "the side, flank; lateral surface."

Kenâri, relating to kenâr, → side.

The angle between a perpendicular at a location, and the → equatorial plane of the Earth. → longitude. See also:
→ astronomical latitude, → celestial latitude, → circle of latitude, → colatitude, → ecliptic latitude, → Galactic latitude, → geocentric latitude, → geodetic latitude, → geographic latitude, → high latitudes, → horse latitudes, → middle latitudes, → spherical latitude, → supergalactic latitude.

L. latitudo "breadth, width, size," from latus "wide," from PIE base *stela- "to spread" (cf. O.C.S. steljo "to spread out," Arm. lain "broad").

Varunâ, from var "breadth, side, breast," variant bar, Tabari vari "width," Mid.Pers. var "breast," Av. varah- "breast" (Sk. vara- "width, breadth") + -u a suffix forming adjectives; Av. vouru- "wide;" + -nâ a suffix of dimension.

1) A regular geometric arrangement of points in a plane or in space.
2) → Crystal lattice.
3) A structure in a nuclear reactor containing nuclear fuel and other materials arranged in a regular geometrical pattern.
4) Math.: A partially ordered set in which each two-element subset has both a greatest lower bound and a least upper bound.

From O.Fr. latiz "lattice," from late "lath, board, plank, batten" (Fr. latte); cf. O.H.G. latta "lath."

Jâré, from jarra "net; snare," Afghan jâli "reticulated garment," Tabari jarazin "grilled apparatus used in a watercourse to gather thatch and trash;" cf. Skt. jāla- "net, snare, lattice."

The energy required to separate an ion from a → crystal to an infinite distance. In other words, the energy released when one → mole of a crystal is formed from gaseous ions.

→ lattice; → energy.

The chord through a focus and perpendicular to then major axis of a conic section.

L. latus "side;" rectum "straight," → right.

Târ "thread, warp, string" (related to tur "net, fishing net, snare," tâl "thread" (Borujerdi dialect), tân "thread, warp of a web," from tanidan, tan- "to spin, twist, weave;" Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch."

Molten → magma released from a volcanic vent or fissure.

Lava, from It. lava "torrent, stream," from L. lavare "to wash;" PIE base *lou- "to wash;" cf. Persian Lori, Kurdi, Malâyeri laf "flood," variants Tabari lé, [Mo'in, Dehxodâ] lur, lây "flood;" Gk. louein "to wash."

Godâzé noun from godâxtan "to melt," from Mid.Pers. vitâxtan, vitâcitan "to melt," from Av. vi-taxti- "flowing away, melting," from vi- "apart, away from, out" (O.Pers. viy- "apart, away;" cf. Skt. vi- "apart, asunder, away, out;" L. vitare "to avoid, turn aside") + tak- "to run, to flow," taciāp- "flowing water," tacinti (3pl.pers.act.) "to flow," tacar- "course," tacan "current, streaming;" Mod.Pers. tâz-, tâxtan "to run; to hasten; to assault," tâzi "swift (greyhound)," tak "running, rush;" Mid.Pers. tâz-, tâxtan "to flow, to cause to walk," tc- "to flow, to walk," tag "running, attack," tâzig "swift, fast;" Khotanese ttajs- "to flow, to walk;" cf. Skt. tak- "to rush, to hurry," takti "runs;" O.Ir. tech- "to flow;" Lith. teketi "to walk, to flow;" O.C.S. tešti "to walk, to hurry;" Tokharian B cake "river;" PIE base *tek^w- "to run; to flow."

1) A rule of conduct or procedure established by custom, agreement, or authority.
2) A code of principles based on morality, conscience, or nature.
3) Physics: A statement of a scientific fact or phenomenon that is invariable under given conditions; e.g. → Newton's law of gravitation, → second law of thermodynamics.
4) Math.: A general principle deduced from particular facts expressed by the statement that a particular phenomenon always occurs if certain conditions are present.

M.E., O.E. lagu, from O.N. *lagu, variant of lag "that which is laid down;" cf. Ger. liegen, E. lay, lie; PIE *legh- "To lie, lay;" compare with Hittite laggari "falls, lies," Gk. lekhesthai "to lie down," L. lectus "bed," O.Ir. lige "bed, tomb," Tokharian lake, leke "bed."

Qânun, from Ar., ultimately from Gk. kanon "rule."
Arté, from O.Pers. arta- "law, justice;" Av. arəta-, ərəta- "law, order," variant aša- "truth, cosmic order," aipi-ərəta- "firmly assigned," from root ar- "to fix;" cf. Skt. rtá- "truth, world order; oath;" Ossetci ard "oath;" Gk. arthon "limb, articulation," artus "a joint;" L. artus "a joint;" PIE base *ar- "to join, to fit together."

An expression that for any triangle relates the length of a side to the cosine of the opposite angle and the lengths of the two other sides. If a, b, and c are the sides and A, B, and C are the corresponding opposites angles: a² = b² + c² - 2bc cos A; b² = c² + a² - 2ca cos B; c² = a² + b² - 2ab cos C.

→ law; → cosine.

Same as → principle of excluded middle.

→ law; → exclude; → middle.

Same as → principle of identity.

→ law; → identity.

Same as → Newton's first law. The → reference frames to which the law applies are called → inertial frames.

→ law; → inertia.

Same as → principle of non-contradiction.

→ law; → non-; → contradiction.

One of the two laws governing reflection of light from a surface: a) The → incident ray, normal to surface, and reflected ray lie in the same plane. b) The → angle of incidence (with the normal to the surface) is equal to the → angle of reflection.

→ law; → reflection.

One of the two laws governing → refraction of light when it enters another transparent medium: a) The → incident ray, normal to the surface, and refracted ray, all lie in the same plane. b) → Snell's law is satisfied.

→ law; → refraction.

In any triangle the sides are proportional to the sines of the opposite angles: a/sin A = b/sin B = c/sin C, where A, B, and C are the three vertices and a, b, and c are the corresponding sides.

→ law; → sine.