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

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.

To name or write in order the letters constituting a word

M.E. spellen, from O.Fr. espeller, from Proto-Germanic spellan "to tell," which also gave rise to the O.E. spellian; ultimately from PIE *spel- "to say aloud, recite."

Vâbidan, from vâb, from vab- ultimately from Proto-Ir. *uab/f- "to call," which has given rise to several words in Iranian languages, mainly Pers. gap "word, talk," gapidan "to talk," buf "owl," zand-vâf "nightingale," literally "song teller, ode singer;" Baluchi gwâp-/gwâpt "to summon, call together;" Sogd. waβ-/wab- "to speak, to talk;" Pash. wây-/wayəl "to speak;" Yaghnobi wov-/wovta "to speak, call."

A person who spells words.

→ spell; → -er.

1) The manner in which words are spelled; orthography; a group of letters representing a word.
2) The act of a speller.

→ spell; → -ing.

1) To pay out, disburse, or expend; dispose of (money, wealth, resources, etc.).
2) To employ (labor, thought, words, time, etc.), as on some object or in some proceeding (Dictionary.com).

M.E. spenden, from O.En. -spendan (in forspendan "use up"), from M.L. spendere, from expendere "to pay out, weigh out money," from → ex- "out" + pendere "to pay, weigh."

Ziyâmidan, from Sogd. zyâm "to consume, spend," ultimately from Proto-Ir. *uz-iam-, from *uz- "out, away," → ex-, + *iam- "to hold, take; stretch, reach out;" cf. Av. yam- "to hold, keep," (+ *apa-) "to take away;" Skt. yam- "to hold, restrain."

A solid geometric figure generated by the revolution of a semicircle about its diameter; equation: x² + y² + z² = r².

M.E. spere, from O.Fr. espere, from L. sphæra "globe, ball, celestial sphere," from Gk. sphaira "globe, ball," of unknown origin.

Koré, loan from Ar. kurat.
Sepehr "sphere, celestial globe, heavens, sky;" Mid.Pers. spihr "sphere, sky, firmament, fate;" Av. spiti- in compounds: spiti-dôiθra- "with clear eyes;" Proto-Iranian *spiθra- (in proper name); cf. Skt. śvitrá- "white, whitish."

The region of space around one of the bodies in a system of two celestial bodies where a third body of much smaller mass is influenced by the gravitational field of that body. The sphere of influence of a planet with respect to the Sun has a radius given by: R = R_P(M_P/M_S)^2/3, where R_P is the radius of the planet's orbit around the Sun, M_P is the mass of the planet, and M_S is the solar mass. The sphere of influence of the Earth has a radius of about 927,000 km or slightly under 150 Earth radii. Beyond this limit, a space probe will come under the influence of the Sun.

→ sphere; → influence.

A series of spheres with varying radii centred on the Earth, each rotating uniformly about an axis fixed with respect to the surface of the next larger sphere, all comprising a model in Greek astronomy to describe the motions of the heavenly bodies. The spheres turned with different speeds about axes with different orientations. The fixed stars revolved around the Earth by the motion of the most distant sphere to which the stars were thought to be attached. Each of the five planets' (Mercury, Venus, Mars, Jupiter, and Saturn) motion could be described using four spheres. The Sun and the Moon required three spheres each to explain their motions. Therefore, a total of 27 spheres described the behavior of the heavenly bodies in terms of circular motion. Eudoxus was the first person to devise a model that could explain the → retrograde motion of the planets in the sky along a looped curve known as the → hippopede.

→ sphere; Eudoxus (Ευδοξοσ) of Cnidus (c 408 BC - c 355 BC), Greek astronomer and mathematician.

Having the form of a sphere; of or pertaining to a sphere or spheres.

From → sphere + → -ic + → -al.