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

A distance-like quantity derived from → gravitational lensing time delay. It is given by a combination of three angular diameter distances in a strong lens system: D_Δt = (1 + z_L)[D_A(EL)D_A(ES) / D_A(LS)], where z_L is the → redshift of the → gravitational lens, while D_A(EL), D_A(ES), and D_A(LS) are the angular diameter distances from the Earth to the lens, from the Earth to the source, and from the lens to the source, respectively. As each of the distance is proportional to the inverse of H₀, D_Δt is proportional to 1/H₀.

→ time; → delay; → distance.

A phenomenon related to special and general relativity.
1) In → special relativity, the apparent shortening of time that occurs at speeds approaching that of light. A clock moving relative to a stationary observer will appear to slow down by a factor √(1- v²/c²), where v is the velocity and c the speed of light. → twins paradox.
2) In → general relativity, a clock in a stronger gravitational field runs more slowly. The dilation factor is given by: √(1- 2GM/rc²), where G is the gravitational constant, M the mass of the object creating the gravitational field, r a radial coordinate of the observer, which is analogous to the classical distance from the center of the object, and c the speed of light.

→ time; dilation, verbal noun of dilate, from M.E. dilaten, from O.Fr. dilater, from L. dilatare "make wider, enlarge," from → dis- "apart" + latus "wide."

Farâxeš, → dilation; zamân, → time.

One of the → orbital elements, the time when the → secondary body reaches → periapsis.

→ time; → periapsis; → passage.

Same → temporal resolution.

→ time; → resolution.

A transformation operating on time in the equations of motion of a dynamical system in which t is replaced by -t.

→ time; → reversal.

A measure of duration of a specific process, such as → crossing time, → dynamical time scale, → evolutionary time scale, → Kelvin-Helmholtz time scale, → nuclear time scale, → photon escape time, → relaxation time, → star formation time scale.

→ time; → scale.

A → sequence of values of a → variable in successive time order, usually at fixed intervals of time.

→ time; → series.

Any of the 24 zones on the Earth surface delimited by → meridians at approximately 15° intervals. In each time zone a common standard time is used, and the time is one hour earlier than the zone immediately to the east.

→ time; → zone.

The sequence of all natural processes in which the → entropy increases. In other words, the fact that these processes all move in one direction in time and are → irreversible. The past is distinctly different from the future; things always grow older, never younger.

→ time; arrow, M.E. arewe, arwe, from O.E. arwan, earh "arrow," from P.Gmc. *arkhwo (cf. Goth. arhwanza), from PIE base *arku- "bow and/or arrow," source of Latin arcus, → arc.

Peykân "arrow," → Sagitta; zamân, → time.

Of, pertaining to, or describing an → event belonging to the interior of the → light cone.

→ time; → like.

The → space-time interval between two → events if it is real, i.e. ds² > 0.

→ timelike; → interval.

Any mechanical, electric, or electronic device, such as a clock or watch, designed to measure and display the passage of time.

→ time; → piece.

Zamân-šomâr, literally "time counter," from zamân, → time, + šomâr "counter," from šomârdan "to count," from Mid.Pers. ôšmârtan, ôšmurtan "to reckon, calculate, enumerate, account for," from Av. base (š)mar- "to have in mind, remember, recall," pati-šmar- "to recall; to long for," hišmar-, cf. Skt. smar- "to remember, become aware," smarati "he remembers," L. memor, memoria, Gk. mermera "care," merimna "anxious thought, sorrow," martyr "witness."

A metallic chemical element; symbol Sn (L. stannum for → alloys containing → lead). → Atomic number 50; → atomic weight 118.69; → melting point 231.9681°C; → boiling point 2,270°C; → specific gravity 5.75 (gray), 7.3 (white). The element was known in prehistoric times.

M.E., O.E. tin; cf. M.Du., Du. tin, O.H.G. zin, Ger. Zinn, O.N. tin; related to Fr. étain?

Arziz "tin," from Mid.Pers. arziz "tin, lead," arus "white, bright;" Av. ərəzata- "silver," auruša- "white;" cf. Skt. arjuna- "white, shining," rajata- "silver;" Gk. argos "white," arguron "silver," L. argentum "silver," arguere "to make clear," argmentum "argument;" PIE *arg- "to shine, be white, bright, clear."
Qal'y of unknown origin.

Any of the several → absorption bands due to the molecule → titanium oxide that are prominent in the spectra of cool → K and → M stars.

→ titanium oxide; → band.

1) The top, summit, or apex.
2) To tilt or cause to tilt; overturn, upset, or overthrow.

1) M.E. tip, from M.L.G. or M.Du. tip "utmost point, extremity" (cf. Ger. zipfel, a diminutive formation).
2) From, tip noun from tip (v.) "to overturn, upset," from M.E. typen "to upset, overturn."

1) Nok "tip," variant tok.

A technique for deriving extragalactic distances which uses the → luminosity of the brightest → red giant branch stars in old → stellar populations as a → standard candle. For old (> 2-3 Gyr), → metal-poor ([Fe/H] < -0.7) stellar populations, this luminosity is relatively well determined, and the → absolute magnitude of these stars in the I band is roughly constant (M_I = -4.1 ± 0.1).

→ tip; → red giant; → branch; → method.

A rapidly moving → mirror used in → adaptive optics to correct overall movements of the incoming → wavefront of light caused by → atmospheric turbulence. The simplest form of adaptive optics is tip-tilt correction, which corresponds to correction of the tilts of the wavefront in two dimensions. This is done by tipping and tilting the mirror rapidly in response to overall changes in position of a reference star. See also → deformable mirror.

From, tip noun from tip (v.) "to overturn, upset," from M.E. typen "to upset, overturn" + tilt noun from tilt (v.) "to cause to lean, incline, slope, or slant," → tilt; → mirror.

Âyené, → mirror; kaj "turned aside; crooked, bent" (cf. Skt. kubja- "hump-backed, crooked," Pali kujja- "bent," L. gibbus "hump, hunch," Lith. kupra "hump") + -o- "and" + râst→ right + -gar agent noun suffix → -or.

Exhausted of strength and energy.

Past participle of tire "to weary; become weary," M.E. tyren, O.E. teorian, of unknown origin.

Xasté "tired; hurt, wounded;" Mid.Pers. xastan, xad- "to injure, wound;" Av. vīxaδ- "to crush;" Proto-Iranian *xad- "to wound, hurt."

The hypothesis that photons from distant objects lose energy during their intergalactic journey to us, thereby increasing in wavelength and becoming redshifted. This would provide an alternative to the → Big Bang model in accounting for the → redshifts of distant galaxies. However, there is no evidence for any such tired-light effect. First discussed by F. Zwicky (1929, Proceedings of the National Academy of Sciences, 15, 773).

→ tired; → light.

In celestial mechanics, a combination of orbital elements commonly used to distinguish between comets and asteroids. Objects whose Tisserand's parameter value is smaller than 3 are considered to be dynamically cometary, and those with a value larger than 3 asteroidal. Also called Tisserand's invariant.

Named after François Félix Tisserand (1845-1896), French astronomer, Director of the Paris Observatory (1892).