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

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.

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.

→ 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.

→ Taylor-Couette flow; → instability.

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

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.

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

To impart knowledge or skill to; give instruction to.

M.E. techen, O.E. tæcan; cf. O.H.G. zihan, Ger. zeihen "to accuse," Goth. ga-teihan "to announce;" cognate with Pers. dis, → form.

Âmuxtan, âmuz- "to teach; learn;" Mid.Pers. hammoxtan, hammoz- "to teach; learn;" cf. Sogd. muck "teacher;" Choresmian mxs "to learn," mwcy "to teach, instruct;" Proto-Iranian *mauc- "to learn; teach."

A radioactive chemical element which does not exist naturally on Earth; symbol Tc. Atomic number 43; mass number of most stable isotope 98; melting point 2,200°C; boiling point 4,877°C. Technetium is synthesised via the → s-process in deep layers of → asymptotic giant branch stars.

From the Gk. technetos "artificial," initially called masurium.

The body of specialized procedures and methods used in any specific field, especially in an area of applied science.

From Fr. technique "formal practical details in artistic expression," noun use of adj. technique "of art, technical," from Gk. tekhnikos, from tekhne "art, skill, craft, method, system;" cognate with Pers. tarâš- "to cut, hew; scape; shave," tišé "axe," as below.

Tašnik, related to Pers. tarâšidan "to cut, hew; scape; shave;" Mid.Pers. tâšitan "to cut, cleave; create by putting together different elements;" from Av. taš- "to cut off, fashion, shape, create," taša- "axe" (Mod.Pers. taš, tišé "axe;" tarâšidan "to shave"), tašan- "creator;" cf. Skt. taks- "to fom by cutting, tool, hammer, form," taksan- "wood-cutter, carpenter;" Gk. tekton "carpenter," tekhne "art, skill, craft, method, system;" L. textere "to weave;" PIE *teks- "to fashion."
Fann or fan, from Pers. fan "way, manner, mode, art, science," related to Mod/Mid.Pers. pand "path, advice, counsel;" Khotanese pande "road, path;" Ossetic fœndœg "path, road;" O.Pers. paθi- "path, way;" Av. paθ- "path, way," variants paθi-, paθā-, pantay-; cf. Skt. pánthā- "road, path, course;" Gk. patos "path, way," pontos "sea;" L. pons "bridge, path;" P.Gmc. *finthanan "to find;" E. find; PIE base *pent- "to go, to tread."

The use of scientific knowledge for the creation and development of devices, machines, and techniques to achieve a commercial, industrial, or scientific objective.

From Gk. tekhnologia "systematic treatment of an art, craft, or technique," originally referring to grammar, from tekhno-, from tekhne, → technique, + → -logy.

The science or art of assembling, shaping, or ornamenting materials in construction; the constructive arts in general. → plate tectonics

L.L. tectonicus, from Gk. tektonikos "pertaining to building," from tekton (genitive tektonos) "builder, carpenter," → technique.

Sâzânik, from sâzân pr.p. of sâz-, sâxtan "to build, make, fashion; to adapt, adjust, be fit" (Mid.Pers. sâxtan, sâz-, Manichean Parthian s'c'dn "to prepare, to form;" Av. sak- "to understand, to mark," sâcaya- (causative) "to teach") + -ik, → -ics.

The first genuine → brown dwarf, discovered in 1995. It is located in the → Pleiades open cluster at approximately 400 → light-years. Teide 1 is a faint object of apparent magnitude I = 19.03, with a late → M dwarf spectral type (M8), corresponding to 55±15 → Jupiter masses (Rebolo et al. 1995, Nature 377, 129).

Named for Observatorio del Teide, Teide Observatory (Tenerife, Canary Islands, Spain), where this object was first detected.

Small glassy bodies whose chemical composition is unrelated to the geological formation in which they are found. They are found mostly in Australia, Java, Philippines and Indochina. Tektites are now thought to have been produced by the impact of meteorites on the earth's surface.

From Gk. tekt(os) "molten" + -ite a suffix used in the name of minerals and fossils.

A combining form meaning "distant."

From Gk. tele-, combining form of tele "far off, afar, at or to a distance," related to teleos "end, goal, result, perfection."

Dur- "far," from Mid.Pers. dūr "far, distant, remote;" O.Pers. dūra- "far (in time or space)," dūraiy "afar, far away, far and wide;" Av. dūra-, dūirē "far," from dav- "to move away;" cf. Skt. dūrá- "far; distance (in space and time);" PIE base *deu- "to move forward, pass;" cf. Gk. den "for a long time," deros "lasting long."

The science and technology of measurement and transmission of data by optical, acoustical, or radioelectric means from remote sources, as from space vehicles, to receiving stations for recording and analysis.

→ tele- + → -metry.

An instrument used to collect and amplify light or other energy. → Refracting telescopes gather light by means of a lens, → reflecting telescopes by means of a mirror. → Radiotelescopes gather radio energy by using an antenna. Telescopes have also been built that can gather X rays, gamma rays, and other forms of energy. → grazing incidence telescope.

From It. telescopio (used by Galileo, 1611), and Mod.L. telescopium (used by Kepler, 1613), both from Gk. teleskopos "far-seeing," from → tele- "far" + -skopos "seeing," from skopein "to watch, look, behold;" → -scope.

Durbin, from dur-, → tele-, + -bin "to see; seer," → -scope.

A covering, usually hemispherical, that is rotatable about a central axis. There is a slit opening along one side wide enough to allow a telescope to be directed at any vertical angle up to 90°.

→ telescope; → dome.

The accuracy with which a telescope can be pointed to a particular coordinate in the sky.

→ telescope; → pointing; accuracy.

The Telescope. An inconspicuous constellation situated in the southern hemisphere, at 19h right ascension, 50° south declination. Abbreviation: Tel; genitive: Telescopii.

Telescopium was named by Abbé Nicolas Louis de Lacaille (1713-1762); → telescope.

The tenth of Saturn's known satellites. It is irregularly-shaped and has a diameter of 29 x 22 x 20 km. Telesto orbits Saturn at a distance of 294,660 km. Telesto is co-orbital with Tethys, residing in Tethys' leading Lagrangian point (L4). The images taken by the Cassini probe during its distant flyby on October 11, 2005 show that its surface is surprisingly smooth, devoid of small impact craters. Telesto was discovered by B. Smith, H. Reitsema, S. Larson, J. Fountain in 1980 from ground-based observations.

In Gk. mythology Telesto was a daughter of Oceanus and Tethys.