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

→ arithmetic progression.

→ arithmetic; → sequence.

A phenomenon that follows and is caused by some previous phenomenon.

From O.Fr. consequence "result," from L. consequentia, from consequentem (nom. consequens), prp. of consequi "to follow after," from &arr; com- "with" + sequi "to follow," (cf. Skt. sacate "accompanies, follows," Av. hacaiti, Gk. hepesthai "to follow"), from PIE base *sekw- "to follow".

Peyâmad, from pey "after; footstep; foot" (Mid.Pers. pay "step, after," O.Pers. nipadiy "on the track of, close after," from ni-, → ni- (PIE), + padiy, from pad- "foot", Av. paδa- "step, footstep," Skt. padá- "step, foorstep;" cf. Gk. pos, L. pes; PIE root *pod-/*ped-) + âmad "to come, arrive," shortened infinitive of âmadan, Mid.Pers. âmatan, O.Iranian *āgmatani, O.Pers., Av. gam- "to come; to go," Av. jamaiti "goes," Skt. gamati "goes," Gk. bainein "to go, walk, step," L. venire "to come," Tocharian A käm- "to come," O.H.G. queman "to come," E. come; PIE root *gwem- "to go, come."

An infinite sequence of integers, starting with 0 and 1, where each element is the sum of the two previous numbers. For example: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ... As the sequence develops, the ratio of the consecutive terms converges to the → golden ratio, about 1.618.

Leonardo Pisano Fibonacci (1170-1250), medieval Italian mathematician who wrote Liber abaci (1202; Book of the Abacus), the first European work on Indian and Arabian mathematics, which introduced "Arabic" numerals in Europe; → sequence.

A scaling relation between the → star formation rate (SFR) in galaxies and the total stellar mass (M_*) of the galaxies. This relation, colloquially called the "galaxy main sequence," extends over several orders of magnitudes in M_* and out to → high redshifts, with a modest scatter of ~ 0.3 dex which includes both intrinsic scatter and measurement uncertainties. The existence of such tight scatter at all observed epochs suggests that most galaxies assembled their stellar mass fairly steadily rather than predominantly in → starburst episodes, implying that → mergers have a sub-dominant contribution to the global star formation history (Wuyts et al., 2011 ApJ 742, 96).

→ galaxy; → main; → sequence.

→ geometric progression.

→ geometric; → sequence.

→ harmonic progression.

→ harmonic; → sequence.

A classification scheme in which galaxies are ordered into a sequence based on their morphology. Same as the → Hubble classification.

→ Hubble; → sequence.

A → main sequence star whose mass is less than 1.5 Msun. Lower main sequence stars generate their energy chiefly through the → proton-proton chain. The core is surrounded by a → radiative zone above which lies a → convective envelope. In such stars the → opacity at the surface is high because of the low → surface temperature. Therefore, radiation cannot carry all the radiation because of high opacity. Thus, energy transfer takes place by → convection to the outer layer.

→ lower; → main; → sequence.

An evolutionary stage in the life of a star when it generates its energy by the conversion of hydrogen to helium via → nuclear fusion in its core. Stars spend 90% of their life on the main sequence. On the → Hertzsprung-Russell diagram it appears as a track running from top left (high temperature, high luminosity, high mass) to lower right (low temperature, low luminosity, low mass). See also → zero age main sequence (ZAMS), → terminal age main sequence (TAMS).

→ main; → sequence.

The method of determining the distance to a star cluster by overlaying its main sequence on the theoretical zero-age main sequence and noting the difference between the cluster's apparent magnitude and the zero-age main sequence's absolute magnitude.

→ main sequence; → fitting.

The point on the → Hertzsprung-Russell diagram of a star cluster at which stars begin to leave the → main sequence and move toward the → red giant branch. The main-sequence turnoff is a measure of age. In general, the older a star cluster, the fainter the main-sequence turnoff. Same as → turnoff point.

→ main sequence; → turnoff.

A star that has evolved off the → main sequence.

→ post-; → main sequence; → star.

A → binary system whose components are → pre-main sequence stars.

→ pre-; → main sequence; → binary.

A → Herbig AeBe star displaying → forbidden emission lines in its spectrum.

→ pre-; → main; → sequence; → B[e] star.

A star that evolves in the → Hayashi phase and has not yet reached the → zero-age main sequence.

→ pre-; → main sequence, → star.

1) General: The following of one thing after another; succession; something that follows; connected line of events, ideas, etc.
2) Math.: A set of quantities that are ordered in some way, such as a₁, a₂, a₃, .... A sequence is said to be known if a formula can be given for any particular term using the preceding terms or using its position in the sequence. Special types of sequences are commonly called → progressions. The terms of a sequence, when written as an indicated sum, form a → series.

M.E., from O.Fr. sequence "answering verses," from M.L. sequentia "a following, a succession," from L. sequentem (nominative sequens), pr.p. of sequi "to follow;" PIE base *sek^w- "to follow;" cf. Pers. az from; Mid.Pers. hac "from;" Av. hac-, hax- "to follow," hacaiti "follows" (O.Pers. hacā "from;" Av. hacā "from, out of;" Skt. sácā "with"); Skt. sácate "accompanies, follows;" Gk. hepesthai "to follow;" Lith. seku "to follow."

Peyâyé, literally "that follows; a subsequent event," from pey "after; step," related to pâ "foot" (Mid.Pers. pâd, pây, Av. pad-, Skt. pat, Gk. pos, gen. podos, L. pes, gen. pedis, P.Gmc. *fot, E. foot, Ger. Fuss, Fr. pied; PIE *pod-/*ped-) + ây- present stem of âmadan "to come, arrive, become" (Av. ay- "to go, to come," aēiti "goes;" O.Pers. aitiy "goes;" Skt. e- "to come near," eti "arrival;" L. ire "to go;" Goth. iddja "went," Lith. eiti "to go;" Rus. idti "to go") +-é nuance suffix.
Rešté "thread, line, rope, row," p.p. of reštan, risidan "to spin;" Mid.Pers. rištag "rope, string, thread;" Av. uruuaēs- "to turn around," uruuaēsa- "vortex in water;" cf. Skt. vréśī- "an appellation of waters;" Gk. rhiknos "crooked;" Lith. rišti "tie, bind;" O.H.G. rīho "knee-bend."

The locus of stars on the → Hertzsprung-Russell diagram that are at the point of exhausting hydrogen in their cores. TAMS forms the upper luminosity boundary of the → main sequence strip. See also → zero age main sequence (ZAMS).

→ terminal; → age; → main; → sequence.

A → main sequence star with a mass above 1.5 Msun. Upper main sequence stars have high central temperatures so that they produce their energy through the → CNO cycle. The outward energy flux is very high and therefore this flux cannot be maintained by → radiative transfer. Thus, upper main sequence stars have → convective cores. Outside the core, there is a → radiative zone. The mass of the convective core gradually diminishes as the hydrogen is consumed. The surface hydrogen is fully ionized and the → opacity is due to → electron scattering The opacity due to electron scattering.

→ upper; → main; → sequence.

The position on the → Hertzsprung-Russell diagram for newborn stars which have just started → hydrogen burning in their cores. The ZAMS forms the lower luminosity boundary of of the → main sequence strip. See also → terminal age main sequence (TAMS).

→ zero; → age; → main sequence.