1) A measure of the energy that is not available for work during a
→ thermodynamic process.
It is defined by dS = dQ/T, where dS is the differential change in
entropy, dQ is the differential amount of heat introduced to the system in
a → reversible process, and T the
→ absolute temperature of the system.
Entropy remains constant during → reversible processes
and increases during → irreversible processes without ever
decreasing. According to the → second law of thermodynamics, an
→ isolated system evolves toward a state of maximum entropy.
See also → Maxwell's demon.
From Ger. Entropie, coined 1865 by physicist Rudolf Clausius (1822-1888) from Gk. entropia "a turning toward," from en- "in" + trope "a turning, change," related to tropos "a turn, way, manner," from tropein "to turn," from PIE base *trep- "to turn" (cf. L. trepit "he turns").
Dargâšt, from dar "in" + gâšt present stem of gâštan "to cause to revolve, to turn," transitive of gaštan, variant gardidan "to turn, to change" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" cf. Skt. vartati; L. vertere; O.H.G. werden "to become;" PIE base *wer- "to turn, bend").
1) An act of entering; → entrance.
M.E. entre(e), from O.Fr. entree, from L. intrata, p.p. of intrare "to → enter."
Darâyé, noun from darây present stem of darâmadan, darâyidan, → enter, + -é noun suffix.
A shell of dust or gas expanding out from an astronomical object such as a star or a comet's nucleus.
From Fr. enveloppe, from O.Fr. envoloper "to envelop," from en- "in" + voloper "wrap up," of obscure origin, perhaps related to M.L. aluppa "a very thin piece or slice of wood" and influenced by L. volvere "to roll."
Pušé, noun from pušidan "to cover; to put on;" Mid.Pers. pôšidan, pôš- "to cover; to wear;" cf. Mid.Pers. pôst; Mod.Pers. pust "skin, hide;" O.Pers. pavastā- "thin clay envelope used to protect unbaked clay tablets;" Skt. pavásta- "cover," Proto-Indo-Iranian *pauastā- "cloth."
1, 2, 3) pargir (#); 3) zistbum
1) An aggregate of surrounding → circumstances,
→ conditions, or → influences
in which a thing is situated or is developed.
From environ + -ment; the first component from Fr. environs, plural of O.Fr. environ "compass, circuit," from environ (adv.) "around," from en- "in" + viron "circle, circuit," from virer "to turn."
Pargir, from par- "around, surrounding," variant pirâ-→ circum- + gir agent noun and
present stem of gereftan "to take, seize; to make prisoner; to intercept"
(Mid.Pers. griftan; Av./O.Pers. grab- "to take, seize;" cf.
Skt. grah-, grabh- "to seize, take," graha
"seizing, holding, perceiving;" M.L.G. grabben "to grab,"
from P.Gmc. *grab; E. grab "to take or grasp suddenly;"
PIE base *ghrebh- "to seize").
1) The time that must be added to the lunar year (12 lunations) to make it coincide
with the solar year (about 11 days).
From Fr. épacte, from L. epacta, from Gk. epaktos, verbal adj. of epagein "to intercalate, add, bring forward," from epi "on" + ag-, from agein "to bring, to lead;" cf. L. agere "to drive, set in motion," → act.
Barafzâ, from bar- "on, upon, up" (Mid.Pers. abar; O.Pers. upariy "above; over, upon, according to;" Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + afzâ, afzudan "to add, increase" (Mid.Pers. abzudan "to increase, grow;" O.Pers. abijav- "to increase, add to, promote," from abi-, aiby- "in addition to; to; against" + root jav- "to press forward;" Av. gav- "to hasten, drive;" Sk. jav- "to press forward, impel quickly, excite," javate "hastens").
andargâh (#), tarufté (#), dozdidé (#)
In Old Iranian and Egyptian calendars and much later in the → French Republican Calendar, one of five (or six) days placed between the 30th of the last month and the first day of the new year to result in a fixed year of 365 (366) days every year; plural epagomenae. Same as → epagomenal day. See also → sansculottide.
Andargâh "intercalary," literally "time between," from andar "between, among,"
→ inter-, + gâh "time;" Mid.Pers. gâh;
O.Pers. gāθu-; Av. gātav-, gātu- "place, throne, spot"
(Skt. gátu- "going, motion; free space for moving; place of abode;"
PIE *gwem- "to go, come").
ruz-e andargâh (#), ~ tarufté (#), ~ dozidé (#)
Fr.: jour épagomène
Same as → epagomena.
A table of computed positions occupied by a celestial body over successive intervals of time such as daily; plural ephemerides.
From L. ephemeris "day book, diary," from Gk. ephemeris "diary, account book," from ephemeros "short-lived, lasting but a day," from → epi "on, upon" + hemerai, dative of hemera "day."
Ruzij, from ruz, → day + zij "astronomical table," from Mid.Pers. zig "astronomical table," originally "string," since the lines of a table were compared to strings used on a weaver's instrument, variant zih, meaning "cord, string" (Modern Persian zeh "cord, string"); Av. jiiā- "bow-string;" cf. Skt. jiyā- "bow-string;" PIE base *gwhi- "thread, tendon" (from which derive also Gk. bios "bow;" L. filum "thread;" Russ. žca "thread").
Fr.: jour des éphémérides
86,400 → ephemeris seconds.
Fr.: méridien des éphémérides
A fictitious meridian that rotates independently of the Earth at the uniform rate implicitly defined by → Terrestrial Dynamical Time (TDT).
Fr.: seconde des éphémérides
The length of a tropical second (1/31,556,925.97474 of the tropical year) on 1900 January 0.5 → ephemeris time.
ephemeris time (ET)
Fr.: Temps des éphémérides
The uniform time-scale used as the independent variable
to calculate the orbits in the solar system prior to 1984. Ephemeris Time was adopted in
1960 to deal with irregularities in the → Earth's rotation
that had been found to affect the
course of mean solar time. The definition of Ephemeris Time is based on Newcomb's analytical
theory of the Earth's motion around the Sun (Newcomb 1898), according to which the geometric
mean longitude of the Sun with respect to the Earth-Moon barycenter is expressed by:
Fr.: transit au méridien des éphémérides
The passage of a celestial body or point across the → ephemeris meridian.
Prefix meaning "upon, at, close upon (in space or time), on the occasion of, in addition."
Gk. epi- "upon, at, close upon (in space or time), on the occasion of, in addition," cognate with O.Pers./Av. apiy-, aipi- "upon, toward, along; also; however;" Skt. api "also, besides."
Prefix api-, from O.Pers./Av. apiy-, aipi-, as above.
1) falak-e tadvir (#); 2) apicarxé
1) In → Ptolemaic system, a circular
→ orbit of a body around a point that itself
orbits circularly another point. Such a system was formulated to explain some
orbits in terms of → circular
motions in a → geocentric
Of or pertaining to an → epicycle.
Fr.: fréquence épicyclique
In the → epicyclic theory of Galactic rotation, the frequency at which a star in the → Galactic disk describes an ellipse around its mean circular orbit. The epicyclic frequency relates to the → Oort's constants. In the solar neighborhood the epicyclic frequency is about 32 km s-1 kpc-1.
Fr.: oscillation épicyclique
Fr.: théorie épicyclique
The theory that describes the Galactic dynamics, that is the orbits of stars and gas clouds in the → Galactic disk, as well as the spiral → density wave. Formulated by Bertil Lindblad (1895-1965), the epicyclic theory assumes that orbits are circular with small deviations. Star orbits are described by the superposition of two motions: i) a rotation of the star (epicenter) around the Galactic center at the circular angular velocity, Ω, and ii) a retrograde elliptical motion at → epicyclic frequency, κ. The epicyclic motion in the Galactic plane occurs in a retrograde sense to conserve → angular momentum. In general Ω and κ are different and, therefore, orbits do not close. However, seen by an observer who rotates with the epicenter, orbits are closed ellipses.
A curve traced by a point of a circle that rolls on the outside of a fixed circle. This curve was described by the Gk. mathematicians and astronomer Hipparchus, who made use of it to account for the apparent movement of many of the heavenly bodies.