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

Of or relating to → spectrophotometry.

→ spectrum; → photometry.

In astronomy, measurement of the absolute fluxes of the components of different frequencies in the spectrum of a light source.

→ spectrum; → photometry.

Of or relating to → spectropolarimetry.

→ spectropolarimetry; → -ic.

A technique of observation in → astrophysics which combines → spectroscopy and → polarization measurements. Spectropolarimetry has a wide range of applications in astrophysics, including → stellar magnetic field studies. → ESPaDOnS, → HARPSpol.

→ spectro-; → polarimetry.

An optical instrument for forming and examining the spectrum of a light source. The instrument contains a narrow slit through which the light enters. The slit is placed at the focus of a positive lens called the collimator lens to form a beam of parallel rays. The beam of light falls on a dispersing element (prism, grating, or grism) which separates the light into its colors. This spectrum can be observed with an ocular (in the spectroscope) or recorded on a detector (in the spectrograph).

→ spectro-; → -scope.

Of or relating to → spectroscopy.

→ spectro-; → -scopy; → -ic.

A binary system that cannot be resolved by a telescope, but can be identified by means of the Doppler shift of the spectral lines. As stars revolve, they alternately approach and recede in the line of sight. This motion is shown up in their spectra as a periodic oscillation or doubling of spectral lines.

→ spectroscopic; → binary.

The situation in which spectroscopic features in a certain optical region are not sensitive enough to distinguish adjacent → luminosity classes, for instance → dwarf stars from → giant stars.

→ spectroscopic; → degeneracy.

A spacial → Hertzsprung-Russell diagram (HRD) which is independent of distance and extinction measurements. The sHRD is derived from the classical HRD by replacing the luminosity (L) to the quantity ℒ = T ⁴_eff/g which is the inverse of the flux-weighted gravity introduced by Kudritzki et al. (2003). The value of ℒ can be calculated from stellar atmosphere analyses without prior knowledge of the distance or the extinction. In contrast to the classical T_eff-log g diagram (→ Kiel diagram), the sHRD sorts stars according to their proximity to the → Eddington limit, because ℒ is proportional to the Eddington factor Γ = L/L_Edd according to the relation ℒ = (1/4πσG)(L/M) = (c/(σκ)Γ, where σ is the → Stefan-Boltzmann constant, κ is the electron → scattering  → opacity in the stellar envelope, and the other symbols have their usual meanings (Langer, N., Kudritzki, R. P., 2014, A&A 564, A52, arXive:1403.2212, Castro et al., 2014, A&A 570, L13.

→ spectroscopic; → H-R diagram.

The stellar mass derived from → gravity (g) and radius (R), expressed by M = gR²/G, where G is the → gravitational constant. Spectroscopic mass conveys the actual mass of the star, in contrast with its → initial mass.

→ spectroscopic; → mass.

The measurement of a stellar distance by the absolute magnitude derived from the luminosity criteria of the spectrum and the apparent magnitude of the star.

→ spectroscopic; → parallax.

A → variable star that displays changes in its → spectrum. In such stars line intensities may vary and new lines may appear. Examples include → AG Carinae, HD 108, HD 191612, and HD 148937.

→ spectroscopic; → variable.

The study of spectral lines from different atoms and molecules. Spectroscopy is an important part of studying the physical and chemical properties of astronomical objects.

Spectro- combining form of → spectrum + → -scopy.

The → electromagnetic radiation divided into its constituting wavelengths or frequencies.

From L. spectrum "appearance, image, apparition," from specere "to look at, view;" Gk. skopein "to behold, look, consider," skeptesthai "to look at;" PIE base *spek- "to see;" cf. Av. spas-, spaš- "to attend to; to serve; spy," spasiieiti "looks at, perceives" (Mod.Pers. sepâs "kindness, favor, thanksgiving," sepâsidan "to praise for benefits received);" Skt. paś- "to see, watch," spasati "sees;" L. specere "to look at;" O.H.G. spehônn "to spy," Ger. spähen "to spy."

Binâb "a vision;" Mid.Pers. wênâb "vision," from wên-, present stem of didan "to see;" 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."

The reflection of light waves in which the reflected waves travel in a definite direction, and the directions of the incident and reflected waves make equal angles with a line perpendicular to the reflecting surface. Same as → regular reflection; opposite of → diffuse reflection.

From L. specularis, from speculum "mirror;" → reflection.

Bâztâb, → reflection; âyenevâr "mirror-like," from âyené, → mirror + -vâr similarity suffix.

To guess possible answers to a question when there are not enough information to be certain.

Back formation from O.Fr. speculation, from L. speculatus, p.p. of speculari "to watch over, observe," from specula "watch tower," from specere "to look at, regard," cognate with Av. spas- "to attend; to serve," spasiieiti "looks at, perceives;" Pers. sepâs "kindness, thanksgiving;" Skt. spasati "sees;" Gk. skopein "to behold, look, consider," skeptesthai "to look at;" O.H.G. spehhon "to spy;" Ger. spähen "to spy;" PIE *spek- "to look around, observe."

Gâsidan infinitive from gâs, from Av. kas- "to look at, see," with extension of the vowel and change of the last phoneme from k to g, as in and cognate with negâh (Mid.Pers. nikâh), → look, âgâh (Mid.Pers. âkâh) "aware" (→ Space Situational Awareness), pargast "God forbid!," and maybe (Lori, Laki, Torbat-Heydarie-yi) gâs "perhaps," (Shirâzi, Fasâyi) gâsam "maybe;" cf. Skt. kāś- "to become visible, appear;" Gk. tekmor, tekmar "sign, mark;" PIE base *k^wek- "to appear, show."

The act or an instance of speculating.

Verbal noun of → speculate.

1) The faculty or power of speaking; oral communication; ability to express one's thoughts and emotions by speech sounds and gesture (Dictionary.com).
2) A form of communication in spoken language, made by a speaker before an audience for a given purpose (Dictionary.com).

M.E. speche; O.E. spæc; cf. Dan. sprog, O.S. spraca, O.Fris. spreke, Du. spraak, O.H.G. sprahha, Ger. Sprache "speech."

Soxan "speech, utterance, word;" Mid.Pers. saxwan "word, speech;" O.Pers. θaⁿh- "to declare, say," aθaham "I said;" Av. səngh- "to declare," sənghāmi "I say;" cf. Skt. śams- "to praise, declare;" L. censere "to estimate, think; decide."

The ratio of the distance covered to the time taken by a moving body. Speed in a specified direction is → velocity.

M.E. spede "good luck, prosperity, rapidity;" O.E. sped "success, prosperity, advancement;" cf. O.S. spod "success," Du. spoed "haste, speed," O.H.G. spuot "success," O.H.G. spuoten "to haste;" from PIE base *spe- "to thrive, prosper" (cf. Skt. sphā- "to increase, become fat;" L. sperare "to hope;" O.C.S. spechu "endeavor;" Lith. speju "to have leisure").

Tondi "speed," from tond "swift, rapid, brisk; fierce, severe" (Mid.Pers. tund "sharp, violent;" Sogdian tund "violent;" cf. Skt. tod- "to thrust, give a push," tudáti "he thrusts;" L. tundere "to thrust, to hit" (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere "to thrust or bore through;" PIE base *(s)teud- "to thrust, to beat") + noun suffix -i.

Same as → velocity of light.

→ speed; → light.