An Etymological Dictionary of Astronomy and Astrophysics

1. An arrangement of words, numbers, or signs, or combinations of them, in parallel columns, to exhibit a set of facts or relations in a definite, compact, and comprehensive form.
   
2. In particular, → zij

Etymology (EN): M.E.; O.E. tabule; O.Fr. table “board, plank, writing table”
(cf. O.H.G. zabel, Ger. Tafel), both from L. tabula “a board, plank, table,” originally “small flat slab or piece” usually for inscriptions or for games.

Etymology (PE): Jadval, loan from Ar. jadwal.

1. An arrangement of words, numbers, or signs, or combinations of them, in parallel columns, to exhibit a set of facts or relations in a definite, compact, and comprehensive form.
   
2. In particular, → zij

Etymology (EN): M.E.; O.E. tabule; O.Fr. table “board, plank, writing table”
(cf. O.H.G. zabel, Ger. Tafel), both from L. tabula “a board, plank, table,” originally “small flat slab or piece” usually for inscriptions or for games.

Etymology (PE): Jadval, loan from Ar. jadwal.

A flat slab or surface, especially one bearing or intended to bear an inscription, carving, or the like (Dictionary.com).

Etymology (EN): M.E. tablette, from M.Fr. tablete, diminutive from → table.

Etymology (PE): Parnik, literally “laminar, resembling a leaf, leaf-like,” variant parnix [Dehxodâ] “a stone or marble slab, a plane stone,” ultimately from Proto-Ir. *parnika-, from *parn-, *par- “feather; leaf, thin layer;” cf. Av. parəna- “feather,” Skt. parna- “feather; leaf (regarded as the plumage of a tree),” Mod.Pers. par(r) “feather; leaf;” PIE *pornos-, *pernom- “feather” (E. fern and Ger. Farn belong to this family). See also → slate.

A flat slab or surface, especially one bearing or intended to bear an inscription, carving, or the like (Dictionary.com).

Etymology (EN): M.E. tablette, from M.Fr. tablete, diminutive from → table.

Etymology (PE): Parnik, literally “laminar, resembling a leaf, leaf-like,” variant parnix [Dehxodâ] “a stone or marble slab, a plane stone,” ultimately from Proto-Ir. *parnika-, from *parn-, *par- “feather; leaf, thin layer;” cf. Av. parəna- “feather,” Skt. parna- “feather; leaf (regarded as the plumage of a tree),” Mod.Pers. par(r) “feather; leaf;” PIE *pornos-, *pernom- “feather” (E. fern and Ger. Farn belong to this family). See also → slate.

A thin → transition  → layer inside → Sun, between the → differentially rotating 
→ convection zone and the uniformly rotating → radiative zone.
Discovered through → helioseismology, it has raised considerable interest, but its thinness remains still to be explained. Due to its strong → shear, it is believed to play a crucial role in the generation of the → solar magnetic field.

Etymology (EN): Tachocline, from tacho- a combining form meaning “speed,” → tachyon + → -cline “slope.” The term was first coined by Edward A. Spiegel and Jean-Paul Zahn (1992, A&A 265, 106), by analogy to the oceanic → thermocline.

Etymology (PE): Tondâšib, from tondâ, → velocity, + šib, → -cline.

A thin → transition  → layer inside → Sun, between the → differentially rotating 
→ convection zone and the uniformly rotating → radiative zone.
Discovered through → helioseismology, it has raised considerable interest, but its thinness remains still to be explained. Due to its strong → shear, it is believed to play a crucial role in the generation of the → solar magnetic field.

Etymology (EN): Tachocline, from tacho- a combining form meaning “speed,” → tachyon + → -cline “slope.” The term was first coined by Edward A. Spiegel and Jean-Paul Zahn (1992, A&A 265, 106), by analogy to the oceanic → thermocline.

Etymology (PE): Tondâšib, from tondâ, → velocity, + šib, → -cline.

A hypothetical subatomic particle that travels faster than the speed of light.

See also: From tachy- a combining form meaning “swift,” from Gk. tachys “swift” + → -on.

A hypothetical subatomic particle that travels faster than the speed of light.

See also: From tachy- a combining form meaning “swift,” from Gk. tachys “swift” + → -on.

The aquatic larva of → frogs and → toads, having internal gills and a tail (TheFreeDictionary).

Etymology (EN): From M.E. taddepol, from tadde “toad” + polle “head,” from M.L.G. or M.Du. pol “head, top.”

Etymology (PE): Vagiz, from Tabari vag “→ frog”

• -iz, -ize diminutive suffix (variants -ce, -že, -ak, Mid.Pers -cak).

The aquatic larva of → frogs and → toads, having internal gills and a tail (TheFreeDictionary).

Etymology (EN): From M.E. taddepol, from tadde “toad” + polle “head,” from M.L.G. or M.Du. pol “head, top.”

Etymology (PE): Vagiz, from Tabari vag “→ frog”

• -iz, -ize diminutive suffix (variants -ce, -že, -ak, Mid.Pers -cak).

A shorter → horseshoe orbit confined to the → Lagrangian points L4 or L5.

See also: → tadpole; → orbit.

A shorter → horseshoe orbit confined to the → Lagrangian points L4 or L5.

See also: → tadpole; → orbit.

1. The part that sticks out at the back of an animal’s body, and that it can move.
   

2. Anything resembling such an appendage in form or position.
   

3. → cometary tail.

Etymology (EN): M.E.; O.E. tægl, from P.Gmc. *tagla- (cf. O.H.G. zagal, Ger. Zagel “tail,” O.N. tagl “horse’s tail”).

Etymology (PE): Dom, variant domb, “tail;” Mid.Pers. dumb “tail;” Av. duma- “tail”; donbâlé, from domb + -âlé, -âl resemblance suffix, → -al.

1. The part that sticks out at the back of an animal’s body, and that it can move.
   

2. Anything resembling such an appendage in form or position.
   

3. → cometary tail.

Etymology (EN): M.E.; O.E. tægl, from P.Gmc. *tagla- (cf. O.H.G. zagal, Ger. Zagel “tail,” O.N. tagl “horse’s tail”).

Etymology (PE): Dom, variant domb, “tail;” Mid.Pers. dumb “tail;” Av. duma- “tail”; donbâlé, from domb + -âlé, -âl resemblance suffix, → -al.

To get into one’s hold or possession by voluntary action; to hold, grasp, or grip (Dictionary.com).

Etymology (EN): M.E. taken “to take, strike, grasp,” O.E. tacan “to grasp, touch,” probably from Old Norse taka “to take, grasp;” cf. M.Du. taken “to grasp;,” Gothic tekan “to touch.”

Etymology (PE): Gereftan “to take, seize, hold;” Mid.Pers. griftan, gir- “to take, hold, restrain;” O.Pers./Av. grab- “to take, seize;”
cf. Skt. grah-, grabh- “to seize, take,” graha- “seizing, holding, perceiving;” M.L.G. grabben “to grab;” E. grab “to take or grasp suddenly;” PIE *ghrebh- “to seize;” see also → assumption, → concept.

To get into one’s hold or possession by voluntary action; to hold, grasp, or grip (Dictionary.com).

Etymology (EN): M.E. taken “to take, strike, grasp,” O.E. tacan “to grasp, touch,” probably from Old Norse taka “to take, grasp;” cf. M.Du. taken “to grasp;,” Gothic tekan “to touch.”

Etymology (PE): Gereftan “to take, seize, hold;” Mid.Pers. griftan, gir- “to take, hold, restrain;” O.Pers./Av. grab- “to take, seize;”
cf. Skt. grah-, grabh- “to seize, take,” graha- “seizing, holding, perceiving;” M.L.G. grabben “to grab;” E. grab “to take or grasp suddenly;” PIE *ghrebh- “to seize;” see also → assumption, → concept.

A white, grey, or pale green soft → mineral with a greasy feel consisting of → hydrated  → magnesium  → silicate, Mg₃Si₄O₁₀(OH)₂.

See also: From M.Fr. talc, from M.L. talcus, talcum, from Ar. talq, from Pers. talk “talc.”

A white, grey, or pale green soft → mineral with a greasy feel consisting of → hydrated  → magnesium  → silicate, Mg₃Si₄O₁₀(OH)₂.

See also: From M.Fr. talc, from M.L. talcus, talcum, from Ar. talq, from Pers. talk “talc.”

A narrative that relates the details of some real or imaginary event, incident, or case; story (Dictionary.com).

Etymology (EN): From M.E., from O.E. talu “series, list, narrative, story;” cognate with Du. taal “speech, language,” Ger. Zahl “number,” O.Norse tala “number, speech,”

Etymology (PE): Matal “tale, history,” of unknown origin.

A narrative that relates the details of some real or imaginary event, incident, or case; story (Dictionary.com).

Etymology (EN): From M.E., from O.E. talu “series, list, narrative, story;” cognate with Du. taal “speech, language,” Ger. Zahl “number,” O.Norse tala “number, speech,”

Etymology (PE): Matal “tale, history,” of unknown origin.

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.

See also: Tambora, proper noun; → volcano

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.

See also: 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.

Etymology (EN): 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.

Etymology (PE): 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.

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.

Etymology (EN): 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.

Etymology (PE): 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.

See also: → tangent + -ial variant of → -al.

Pertaining to or of the nature of a tangent.

See also: → tangent + -ial variant of → -al.

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

See also: → tangential; → motion.

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

See also: → 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.
   

2. 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.

See also: → tangential; → velocity.

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.
   

2. 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.

See also: → tangential; → velocity.

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

See also: Tangentially, adverb of → tangential; → polarized; → light.

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

See also: Tangentially, adverb of → tangential; → polarized; → light.

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

Etymology (EN): M.E.; unexplained variant of tappe; O.E. tæppe “strip (of cloth),” akin to M.L.G. teppen “to tear, pluck.”

Etymology (PE): 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)

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

Etymology (EN): M.E.; unexplained variant of tappe; O.E. tæppe “strip (of cloth),” akin to M.L.G. teppen “to tear, pluck.”

Etymology (PE): 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.

Etymology (EN): 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.

Etymology (PE): Miq, → nebula; roteyl “large, hairy spider, tarantula.”

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.

Etymology (EN): 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.

Etymology (PE): 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.

See also: 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).

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.

See also: 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.

Etymology (EN): 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”).

Etymology (PE): 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.”

An object to be observed with a telescope.

Etymology (EN): 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”).

Etymology (PE): 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.

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

Etymology (PE): Dord “lees, dregs, sediment, tartar of wine.”

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

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

Etymology (PE): 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.

See also: Tartaric, from → tartar; → acid.

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.

See also: 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.

Etymology (EN): M.E., from M.L. tasca, metathetic variant of taxa “tax,” from taxare “evaluate, estimate, handle,” also “censure, charge.”

Etymology (PE): 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.”

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.

Etymology (EN): M.E., from M.L. tasca, metathetic variant of taxa “tax,” from taxare “evaluate, estimate, handle,” also “censure, charge.”

Etymology (PE): 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.

See also: → task; → manager.

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.

See also: → 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.

See also: → Taurus; → -ids.

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.

See also: → 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.

Etymology (EN): 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).

Etymology (PE): 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.”

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.

Etymology (EN): 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).

Etymology (PE): 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.

Etymology (EN): 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.

Etymology (PE): Hamân “same” (Mid.Pers. ham “same; also; together,” → com-) + ân “that.”

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.

Etymology (EN): 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.

Etymology (PE): 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.

See also: → Taylor number; → column.

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.

See also: → 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.

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

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.

See also: 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.

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

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.

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

The → Couette flow between two concentric cylinders with fluid filling the annular region. The flow is generated by the relative rotation of the two cylinders. Under some physical conditions the flow may undergo the → Taylor-Couette instability.

See also: → Taylor number; → flow.

The → Couette flow between two concentric cylinders with fluid filling the annular region. The flow is generated by the relative rotation of the two cylinders. Under some physical conditions the flow may undergo the → Taylor-Couette instability.

See also: → Taylor number; → flow.

A hydrodynamic instability in the → Taylor-Couette flow that arises when the rotation velocity of the fluid exceeds a critical value. The instability arises for → Taylor numbers larger than about 1700.
At the beginning the fluid elements will move in
simple rolls, but turbulence in the form of complex spirals will appear with increasing rotation velocity.

See also: → Taylor-Couette flow; → instability.

A hydrodynamic instability in the → Taylor-Couette flow that arises when the rotation velocity of the fluid exceeds a critical value. The instability arises for → Taylor numbers larger than about 1700.
At the beginning the fluid elements will move in
simple rolls, but turbulence in the form of complex spirals will appear with increasing rotation velocity.

See also: → Taylor-Couette flow; → instability.

Fluid mechanics: A second order differential equation that governs the vertical structure of a perturbation in a stratified parallel flow.

See also: Named after G. I. Taylor (Effect of variation in density on the stability of superposed streams of fluid, 1931, Proc. R. Soc. Lond. A, 132, 499), → Taylor number, and S. Goldstein (On the stability of superposed streams of fluids of different densities, 1931, Proc. R. Soc. Lond. A, 132, 524); → equation.

Fluid mechanics: A second order differential equation that governs the vertical structure of a perturbation in a stratified parallel flow.

See also: Named after G. I. Taylor (Effect of variation in density on the stability of superposed streams of fluid, 1931, Proc. R. Soc. Lond. A, 132, 499), → Taylor number, and S. Goldstein (On the stability of superposed streams of fluids of different densities, 1931, Proc. R. Soc. Lond. A, 132, 524); → equation.

In a rapidly rotating fluid, the fluid velocity is constant along any line parallel to the axis of rotation.

See also: → Taylor number; Joseph Proudman (1888-1975), British mathematician and oceanographer.

In a rapidly rotating fluid, the fluid velocity is constant along any line parallel to the axis of rotation.

See also: → Taylor number; Joseph Proudman (1888-1975), British mathematician and oceanographer.