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

The noise in a radio telescope, composed of the receiver noise and the sky noise.

→ system; → noise.

Having, showing, or involving a system, method, or plan.

L.L., from Gk. systematikos; → system; → -ic.

Râžmânvâr, râžmânmand, from râžmân, → system, + -mand suffix of possession.

The error that is constant in a series of repetitions of the same experiment or observation. Usually, systematic error is defined as the expected value of the overall error. opposite of → random error.

→ systematic; → error.

Biology: The science that deals with the systematic naming and classification of all kinds of organisms.

From → systematic + → -ics.

Relating to or affecting a system as a whole.

→ system; → -ic.

An interdisciplinary field of science which deals with the nature of complex systems in nature, society, and science, and studies complex parts of reality as systems.

→ system; → theory.

The alignment of three or more celestial bodies in the same gravitational system along a nearly straight line.
Conjunction or opposition of a heavenly body with the Sun.

From L.L. syzygia, from Gk. syzygia "yoke, pair, union of two, conjunction," from syzygein "to yoke together," from → syn- "together" + zygon "yoke," cognate with Pers. yuq, jug "yoke," as below.

Yujân from yuj "yoke," variants yuq, juh (Mid.Pers. jug, ayoxtan "to join, yoke;" Av. yaog- "to yoke, put to; to join, unite;" cf. Skt. yugam "yoke;" Hittite yugan "yoke;" Gk. zygon "yoke," as above, zeugnyanai "to join, unite;" L. jungere "to join," O.C.S. igo, O.Welsh iou, Lith. jungas O.E. geoc. PIE base *yeug- "to join") + -ân suffix of place and time.

A → stellar association containing many → T Tauri stars. Examples include the Taurus-Auriga T association, the nearby → TW Hydrae association, and Vela T1 and T2.

T, letter of alphabet; → association.

A type of → brown dwarf with an → effective temperature between about 1200 K and 500 K, i.e. colder than the preceding type → L dwarf. The spectra of T dwarfs are characterized by the presence of → methane (CH₄) bands in the → near infrared. The presence of these bands, broad H₂O features, and H₂ collision-induced absorption radically alter the spectral energy distributions of T dwarfs compared to a black body at the same temperature. Hence near-infrared colors become increasingly blue (J - K ~ 0) as compared to L dwarfs. The first T dwarf, called → Gl 229B, was discovered by Nakajima et al. (1995, Nature 378, 463). The spectral classification scheme (subtypes T0 to T9) currently used was defined by Burgasser et al. (2002, ApJ 564, 421).

For the reasoning behind the choice of the letter T, see Kirkpatrick et al. 1993, ApJ 406, 701; → dwarf.

The most famous young stellar object, the prototype of → T Tauri stars which is located in the Taurus-Auriga star forming region at a distance of about 140 pc. T Tauri is about 2.4 solar masses and about 7 million years old. Complex structures of shock heated gas indicative of outflows surround the star, both on sub-arcsecond and larger scales. The → accretion rate is estimated to be (3-6) x 10^-8 solar masses per year. T Tauri has a companion (about 0.7 arcseconds apart) which is invisible in the optical and has been observed to be strongly variable in infrared. It is an intermediate mass young star (2.5 solar masses) surrounded by a → circumstellar disk. This star is itself a → close binary, the component being a low mass star (0.6 solar masses) also surrounded by circumstellar material.

T, letter of alphabet; Tauri genitive of → Taurus.

A member of a class of young stellar objects of roughly 1 solar mass showing strong → infrared excess emission attributed to → circumstellar disks and found within or close to molecular clouds. T Tauri stars are → protostars in the final stages of formation to become a stable → main sequence star. The nuclear reactions in their core have not yet stabilised and the stars are known for the variability of their brightness. See also → classical T Tauri star, → weak-line T Tauri star.

→ T Tauri; → star.

The symmetry of physical laws under a time reversal transformation.

T for → time; → symmetry.

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

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.

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).

M.E. tablette, from M.Fr. tablete, diminutive from → table.

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.

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.

Tondâšib, from tondâ, → velocity, + šib, → -cline.

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

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).

From M.E. taddepol, from tadde "toad" + polle "head," from M.L.G. or M.Du. pol "head, top."

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.

→ 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.

M.E.; O.E. tægl, from P.Gmc. *tagla- (cf. O.H.G. zagal, Ger. Zagel "tail," O.N. tagl "horse's tail").

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).

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."

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.