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

The largest volcanic eruption in recorded history, which mainly occurred on April 10, 1815 in the Indonesian Sumbawa Island. An estimated 150 cubic kilometers of igneous material was ejected, whereby the mountain lost ~ 1400 m in height during the blast (current height ~ 2900 m). The eruption created a 6 km-wide, 1250 m-deep → caldera. The ash put into the atmosphere produced high-latitude clouds which intercepted incoming sunlight. The resulting drop in → insolation caused a dramatic change in climate and weather patterns in the Northern Hemisphere during the following year. The year 1816 is known as the "year without a summer" because there was no warm season over much of the Northern Hemisphere.

Tambora, proper noun; → volcano

1) A straight line or plane that touches a curve or curved surface at one and only one point. Conversely, a curve or curved surface that touches a straight line, curve, or curved surface at one and only one point.
2) In trigonometry, the function of an acute angle of a right triangle defined as the ratio of the length of the opposite side to that of the adjacent side.

From L. tangentem (nominative tangens), pr.p. of tangere "to touch," from PIE base *tag- "to touch, to handle" (cf. L. tactus "touch," Gk. tetagon "having seized," O.E. þaccian "stroke, strike gently"); tânžânt, loan from Fr.

1) Sâyân, pr.p. of sâyidan "to touch, to rub," variants sâbidan, pasâvidan; Khotanese sauy- "to rub;" Sogdian ps'w- "to touch;" ultimately Proto-Iranian *sau- "to rub."
2) Tânžânt, loan from Fr.

Pertaining to or of the nature of a tangent.

→ tangent + -ial variant of → -al.

That component of a an object's motion which is perpendicular to the observer's → line of sight.

→ tangential; → motion.

1) The instantaneous linear velocity of a body moving in a circular path. It is equal to the → angular velocity multiplied by the radius: v_t = ωr.
3) The component of the velocity of an object, such as a star, that is at right-angles to the observer's → line of sight; also known as transverse velocity. See also → radial velocity.

→ tangential; → velocity.

The → linearly polarized light that vibrates perpendicularly to an imaginary line joining the source to the point of observation.

Tangentially, adverb of → tangential; → polarized; → light.

A long, narrow strip of paper, plastic, metal, etc., as in → magnetic tape

M.E.; unexplained variant of tappe; O.E. tæppe "strip (of cloth)," akin to M.L.G. teppen "to tear, pluck."

Navâr "a narrow, long piece, strip, rope," cf. Ossetic nawar "tendon, sinew;" Av. snāvarə- "tendon, sinew;" cf. Skt. snāvan- "tendon, sinew;" Pali nahāru-, nhāru- "tendon, muscle;" Hindi nahāru "piece of leather;" Arm. neard "tendon;" Gk. neura "string, sinew;" L. neros "sinew, muscle, nerve;" Ir. sin "chain;" P.Gmc. *senawo (O.S. sinewa, O.N. sina, O.Fris. sine, M.Du. senuwe, O.H.G. senawa, Ger. Sehne, E. sinew)

The largest and brightest → H II region in the → Large Magellanic Cloud. This → giant H II region has a diameter of over 800 → light-years, and contains half a million → solar masses of ionized gas. The ionization is produced by several clusters of → O-type and → B-type stars, including the very powerful and compact cluster → R136 near its centre. The nebula's name comes from its spider-like shape. Also known as → 30 Doradus and NGC 2070.

Tarantula "any of several large, hairy spiders of the family Theraphosidae," from M.L. tarantula, from It. tarantola, from Taranto "seaport city in southern Italy in the region where the spiders are frequently found," from L. Tarentum, from Gk. Taras; → nebula.

Miq, → nebula; roteyl "large, hairy spider, tarantula."

The star Gamma, magnitude 2.72, in the constellation → Aquila. It is a K3 → giant 460 light-years away. Other designations: HR 7525, HD 186791.

Tarazed, from Pers. tarâzu "balance, scales," from šâhin-e tarâzu "the beam of the balance," the name given to the three aligned stars of Aquila, i.e. α, β, and γ (Abdolrahmân Sufi, Book of Fixed Stars, A.D. 964, Pers. translation by Nasireddin Tusi in 13th century). The first word, šâhin, apart from "beam," means "royal" and "falcon." Tarâzu, from Mid.Pers. tarâzên-, tarâzênidan "to weigh;" Proto-Iranian *tarāz-, from *tarā- "balance, scales" (cf. Skt. tulā- "scales, balance, weight," from tul- "to weigh, make equal in weight, equal," tolayati "weighs, balances;" L. tollere "to raise;" Gk. talanton "balance, weight," Atlas "the Bearer" of Heaven;" Lith. tiltas "bridge;" PIE base telə- "to lift, weigh") + Av. az- "to convey, conduct, drive," azaiti drives" (cf. Skt. aj- "to dive, sling," ájati "drives," ajirá- "agile, quick," Gk. agein "to lead, guide, drive, carry off," L. agere "to do, set in motion, drive," from PIE root *ag- "to drive, move," → act).

An object to be observed with a telescope.

M.E., from M.Fr. targuete, from O.Fr. targe "light shield," from Frank. *targa "shield" (cf. O.H.G. zarga "edging, border," Ger. Zarge "edge, border").

Âmâj "aim, goal," from Proto-Iranian base *āma-, from prefix *ā- + *ma- "to measure;" cf. Av. mati- "point, tip;" O.Pers./Av. mā(y)- "to measure;" Pers. mun/mân "measure," as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl;" cf. Skt. mati "measures," matra- "measure," Gk. metron "measure," L. metrum; PIE base *me- "to measure."

A reddish-brown deposit consisting mainly of potassium hydrogen tartrate, which forms during the fermentation of wine. Same as → argol.

From O.Fr. tartre, from L. tartarum, from late Gk. tartaron "tartar encrusting the sides of wine casks," perhaps relating to Pers. dord (?).

Dord "lees, dregs, sediment, tartar of wine."

An organic acid with general chemical formula C₄H₆O₆ that exists in four isomeric forms . The common form, d-tartaric acid, obtained from → tartar, is a white, soluble, crystalline solid. It occurs naturally in many plants, particularly in grapes, bananas, and tamarinds. It is also one of the main acids found in wine.

Tartaric, from → tartar; → acid.

1) A definite piece of work required to be done as a duty or routine job.
2) A matter of considerable labor or difficulty.
3) In computer programming, a basic unit of programming that an → operating system controls.

M.E., from M.L. tasca, metathetic variant of taxa "tax," from taxare "evaluate, estimate, handle," also "censure, charge."

Taš, created from Proto-Ir. root *taš- "to make, construct; to cut;" cf. Av. tāš- "to make, construct; to cut;" O.Pers. (ham)taxš- "to work with, effect;" Mid.Pers. tâš- "to cut, cleave; create;" Mod.Pers. taš, tišé "hatchet, axe, adze," tarâšidan "to shave;" Ossetic I. dasyn/dast "to shave;" Munji tiž-, Yidgha tiž- "to shear;" Pash. toq "to shave;" cf. Skt. taks- "to form (by cutting), to build, prepare;" Gk. tekton "carpenter."

A → software → utility that enables a → user to view each of the tasks currently running on the → computer, each of the → processes, and the overall performance of the computer.

→ task; → manager.

An annual → meteor shower occurring in the constellation → Taurus. There are actually two distinct Taurid meteors: the South and North Taurids. The Southern peaks around 10 October and the Northern about 12 November. The Taurid meteor shower is created by debris left behind by → Encke's comet.

→ Taurus; → -ids.

Th Bull. A large constellation of the → Zodiac, in the northern hemisphere at about 4h 20m right ascension, 16° north declination. Alpha Tauri or → Aldebaran is among the twenty brightest stars in the sky. Taurus contains several star clusters, including the → Pleiades and → Hyades. The famous → Crab nebula is situated to the west of Zeta Tauri. Abbreviation: Tau; Genitive: Tauri.

From L. taurus "bull," from PIE *tauro- "bull" (cf. Gk. tauros; O.C.S. turu "bull, steer;" Lith. tauras "aurochs;" O.Pruss. tauris "bison"), often said to be from PIE *steu-ro- "be big, be strong, be sturdy" (cf. Pers. sotur, Mid.Pers. stôr "horse, mount; large cattle;" Av. staora- "bovine animals;" O.Icelandic stjôrr; Goth. stiur "young bull;" O.E. steor; E. steer).

Gâv "bull, ox, cow;" Mid.Pers. gâw "ox, bull, cow; Taurus;" Av. gao- "cow, ox, bull;" cf. Skt. gaus; Gk. bous "ox;" L. bov-; Armenian kov; O.E. cu; E. cow; PIE base *gwou- "ox, bull, cow."

1) Needless repetition of an idea, especially in words other than those of the immediate context, without imparting additional force or clearness, as in "lifeless dead."
2) A → proposition that is → always  → true. On a → truth table a tautology is a → sentence that is true for every possible → truth value of its constituent parts.

L.L. tautologia "representation of the same thing in other words," from Gk. tautologia, from tautologos "repeating what has been said," from tauto "the same" (contraction of to auto "the same," from to "the" + → auto + -logos "saying," related to legein "to say," → -logy.

Hamân "same" (Mid.Pers. ham "same; also; together," → com-) + ân "that."

A phenomenon in which the relative motion of a homogeneous rotating liquid tends to be the same in all planes perpendicular to the axis of rotation. When a rotating fluid comes into contact with a submerged object, the fluid flows around it as if it were a cylinder extending the entire depth of the fluid parallel to the axis of the system.

→ Taylor number; → column.

A → dimensionless number indicating the relative importance of the → centrifugal and → viscous forces in the → Taylor-Couette flow. It is also called rotational Reynolds number. Its value depends on the length scale of the convective system, the rotation rate, and → kinematic viscosity. The Taylor number Ta is expressed by Ω²Rd³/ν² where Ω is the → angular velocity of the inner cylinder, R = (R₁ + R₂)/2 is the mean radius of the two cylinders, d = R₂ - R₁ is the distance between the cylinders, and ν is → kinematic viscosity. If Ta is equal or greater than one, the rotational effects are significant.

Named after Geoffrey Ingram Taylor (1886-1975), a British physicist, mathematician, and expert on fluid dynamics and wave theory; → number.

A series expansion of an infinitely differentiable function about a point a: Σ (1/n!) (x - a) ⁿ f ⁿ (a), where fⁿ(a) is the n-th derivative of f at a, and the sum over n = 0 to ∞. If a = 0 the series is called a → Maclaurin series.

Named for the English mathematician Brook Taylor (1685-1731); → series.