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

The epoch in the early evolution of the Universe when matter and photons decoupled. Once atoms formed, light and matter stopped constantly interacting with one another, and photons were able to travel freely. As a result, the Universe became transparent. Light from this period is observed today as the → cosmic microwave background radiation. Same as → decoupling era and → recombination era.

→ last; → scattering.

The set of locations in space corresponding to the → last scattering epoch in the early Universe. It is a spherical surface around the present-day observer from which the → cosmic microwave background radiation appears to emanate.

→ last; → scattering; → surface.

Last in order of birth; youngest.

→ last; → born.

Demâzâ, from Lori, Laki demâzâ, from demâ "last, end, back," related to dom, → tail, + zâ contraction of zâd, → born.

Continuing or remaining for a long time; enduring.

→ last; → -ing.

1) Happening or arriving after an expected or arranged time; not on time, beyond usual time.
2) Belonging to an advanced stage or period in the development of something. → Late Heavy Bombardment, → late helium flash, → late thermal pulse, → late-type galaxy, → late-type star.

M.E., from O.E. læt "slow, late;" cf. Ger. lass "slothful;" O.N. latr, Goth. lats "slow, lazy;" L. lassus "tired, faint;" Gk. ledein "to be weary."

Dir "late; tardily, slowly; a long while; old, antique," from Mid.Pers. dêr, variants dagr, drâz "long" (Mod.Pers. derâz "long," variant Laki, Kurdi derež); O.Pers. darga- "long;" Av. darəga-, darəγa- "long," drājištəm "longest;" cf. Skt. dirghá- "long (in space and time);" L. longus "long;" Gk. dolikhos "elongated;" O.H.G., Ger. lang; Goth. laggs "long;" PIE base *dlonghos- "long."
Dirân, adjective, variant of dir, as above.

A cataclysmic event in the history of the → solar system, estimated to have occurred 3.9 billion years ago (about 600 million years after the formation of the → terrestrial planets) during which → asteroid and → comet impacts with Earth were some 20,000 times more frequent than today. It is estimated that during this period the terrestrial planets were bombarded with an object 1 km in size every 20 years. This hypothetical event lasted 50 to 150 million years. Several explanations have been put forward, among which the occurrence of an instability in the outer solar system which caused → orbital migration of small bodies from the → Kuiper belt inward.

→ late, with respect to the formation time of the planets; → heavy; bombardment, noun from bombard, from Fr. bombarder, from bombarde "mortar, catapult" from bombe, from It. bomba, probably from L. bombus "a booming sound," from Gk. bombos "deep and hollow sound."

A → helium flash event that occurs during the → post-AGB phase. Some of the central stars of planetary nebulae (→ CSPN) experience a final → thermal pulse after having achieved a → white dwarf configuration and begun their descent along a → white dwarf cooling track of nearly constant radius. During such a pulse, most of the hydrogen remaining in the star at pulse onset is incorporated into the helium-burning convective shell and completely burned. Following the pulse, the star swells briefly to → red giant dimensions (Iben et al. 1983; ApJ 264, 605).

→ late; → helium; → flash.

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."

1) To throw or propel with force; hurl. → jet launching.
2) To set (a missile, spacecraft, etc) into motion

From M.E. launchen "to throw as a lance," O.Fr. lanchier, lancier "to hurl, throw, cast," from L.L. lanceare "wield a lance," from L. lancea "light spear, lance."

From partâb "a throw, an arrow that flies far," partâbidan "to throw," → ballistics.

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."