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

1) Security against loss or damage or for the fulfillment of an obligation, the payment of a debt, etc.; a pledge, guaranty, or bond.
2) The state or quality of being sure (Dictionary.com).

M.E. surte, from M.Fr., from O.Fr. seurte "a promise, pledge, guarantee; assurance, confidence;" from L. securitas "freedom from care or danger, safety," from securus, → secure.

A current whose core of maximum velocity is near the surface.

→ surface; → current.

1) For a star, same as → effective temperature.
2) Meteo.: The air temperature at or near the earth's surface.

→ surface; → temperature.

The ability of a farm to produce food indefinitely, without causing severe or irreversible damage to → ecosystem health.

→ sustainable; → agriculture.

A relation between two quantities such that the first is to the second as the second is to the first. In symbols: a R b = b R a. For example, multiplication is an operation with a symmetric relation between the factors: 5 x 3 = 3 x 5.

→ symmetric; → relation.

The revolution frequency of a → relativistic particle of charge q and mass m in the → uniform magnetic field B of a synchrotron. It is expressed by: f_syn = qB/2πγm, where γ is the → Lorentz factor. This frequency is lower than → cyclotron frequency for a → non-relativistic case.

→ synchrotron; → frequency.

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.

A physical quantity characterizing the mean random motion of molecules in a physical body. In other words, a measure of the average kinetic energy of the particles of a system.

From L. temperatura "a tempering, moderation," from temperatus, p.p. of temperare "to moderate, to mix." Sense of "degree of heat or cold" first recorded 1670 (Boyle), from L. temperatura, used in this sense by Galileo.

Damâ, from dam "breath of an owen; bellows; smoke; air," also "moment, time," from Mid./Mod.Pers. damidan "to blow, breathe;" Av. dāδmainya- "blowing up;" cf. Skt. dahm- "to blow," dhámati "blows;" Gk. themeros "austere, dark-looking;" Lith. dumti "to blow;" PIE dhem-/dhemə- "to smoke, to blow."

Cosmology: Minute temperature variations of the cosmic microwave background radiation.

→ temperature; → anisotropy.

A physical quantity that describes the rate of change of temperature with displacement in a given direction from a given reference point. Same as → thermal gradient.

→ temperature; → gradient.

Meteo.: A reversal in the normal temperature decrease, the temperature rising with increased elevation in the atmosphere instead of falling. A layer in which temperature increases with altitude.

→ temperature; → inversion.

A measure of the correlation between the phases of an → electromagnetic wave at different points along the direction of propagation. Temporal coherence indicates to what extent a source is monochromatic. Imagine a source emitting waves with wavelength λ ± Δλ. Waves with wavelength λ and λ + Δλ, which at some point in space constructively interfere, will no longer constructively interfere after some path length l_c = λ²/(2πΔλ); l_c is called the → coherence length.

→ temporal; → coherence.

The measure of the ability of an observing system to clearly separate events in time. In other words, the shortest time interval that can be determined between two different events.

→ temporal hour; → resolution.

Pertaining to, consisting of, or representing the Earth as distinct from other planets.

From L. terrestris "earthly," from terra "earth," literally "dry land" (as opposed to "sea"); from PIE base *ters- "to dry" (cf. Pers. tešné "thirsty;" Mid.Pers. tašnak "thirsty;" Av. taršu- "dry," taršna- "thirst;" Skt. trsta- "dry," tars- "to be thirsty;" Gk. teresesthai "to become or be dry," L. torrere "to dry up, roast," Goth. þaursus "dry, barren," O.H.G. derren "to make dry," durst "thirst;" Ger. dürr "arid;" O.E. þurstig "thirsty").

Zamini adj. of zamin, variant zami "earth, floor, land;" Mid.Pers. zamig; Av. zam- "the earth;" cf. Skt. ksam- "the ground, earth;" Gk. khthôn, khamai "on the ground;" L. homo "earthly being" (as in homo sapiens, homicide, humble, humus, exhume), humus "the earth;" O.Russ. zemi "land, earth;" PIE root *dh(e)ghom "earth".

A uniform atomic time scale for apparent geocentric ephemerides defined by a 1979 IAU resolution, which replaced Ephemeris Time. TDT is independent of the variable rotation of the Earth, and the length of the tropical year is defined in days of 86,400 seconds of international atomic time. In 1991 it was replaced by Terrestrial Time.

→ terrestrial; → dynamical; → time.

A parameter representing the product of the → gravitational constant by the Earth's mass. It is 3.987 x 10¹⁴ m³s^-2 or 3.987 x 10⁵ km³s^-2.

→ terrestrial; → gravitational; → constant.

The four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth's. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. These planets are approximately the same size, with the Earth the largest. They are considerably denser than the Jovian planets, ranging from a specific gravity of 4 for Mars to 5.5 for the Earth.

→ terrestrial; → planet.

The modern astronomical standard for the passage of time on the surface of the Earth. It is the → coordinate time scale consistent with the theory of general relativity for an observer on the surface of the Earth. TT was renamed from Terrestrial Dynamical Time (TDT) in 1991. The fundamental unit of TT is the day of 86,400 SI seconds. It is related to the International Atomic Time by the relation: TDT = TAI + 32.184 sec.

→ terrestrial; → time.

A type of hypothetical → topological defect in the structure of → space-time that forms when large, complicated symmetry groups are completely broken.

M.E., from M.Fr., from L. textura "web, texture, structure," from stem of textere "to weave;" PIE base *tek- "to make" → technique.

Bâft, verbal noun, past stem of bâftan "to weave;" Mid.Pers. waf- "to weave;" Av. ubdaēna- "consisting of woven texture," from *ubda- "woven," p.p. from vaf- "to weave; to sing," literally "to weave the songs;" cf. Skt. vabh- "to bind, fetter," ubhnāti "he laces together;" Gk. hyphainein "to weave," hyphos "web;" P.Gmc. *webanan (cf. O.N. vefa, M.L.G., M.Du., Du. weven, O.H.G. weban, Ger. weben; O.E. wefan; E. weave), from PIE *webh-/*wobh- "to weave."

A → proposition, → statement, or → formula in → mathematics or → logic deduced from → axioms, other propositions, → assumptions, → premises, or formulas. Theorems are statements which can be proved. For example, → Fourier theorem; → Liouville's theorem; → Woltjer's theorem.

From M.Fr. théorème, from L.L. theorema, from Gk. theorema "spectacle, speculation," in Euclid "proposition to be proved," from theorein "to look at, speculate, consider."

Farbin, from far- intensive prefix "much, abundant; elegantly; forward" (Mid.Pers. fra- "forward, before; much; around;" O.Pers. fra- "forward, forth;" Av. frā, fərā-, fra- "forward, forth; excessive;" cf. Skt. prá- "before; forward, in front;" Gk. pro "before, in front of;" L. pro "on behalf of, in place of, before, for;" PIE *pro-) + bin, present stem of didan "to see," from Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" cf. Skt. veda "I know;" Gk. oida "I know," idein "to see;" L. videre "to see;" PIE base *weid- "to know, to see."