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

A type of → instability occurring within a → fluid as a result of the → shear caused by → differential rotation. The condition for shear instability is expressed by the → Richardson criterion. Shear turbulence is likely the most efficient → mixing process in stellar → radiative zones.

→ shear; → turbulence.

A wave that occurs in an elastic medium with the disturbances perpendicular to the direction of motion of the wave. Shear waves do not propagate through a fluid. Also called S-wave, secondary wave, and transverse wave.

→ shear; → wave.

The brightest star in the constellation → Cassiopeia. It is a supergiant K0 III star with a visual magnitude of 2.23 at a distance of 230 light-years. It has a large luminosity, 855 times that of our Sun, and a notable size, 48 times that of the Sun. Its effective temperature is 4530 K. Name variants: Schedar, Shedar, and Schedir. Also known as HR 168 and HD 3712.

From Ar. as-sadr (الصدر) "chest, breast," contraction of as-sadr-al-Zat-al-kursi (الصدر‌الذات‌الکرسی) "the chest of the throne's owner" or "the chest of the seated one" referring to the Ar. rendering of the character in Gk. mythology.

A domesticated ruminant mammal with a thick woolly coat and (typically only in the male) curving horns. It is kept in flocks for its wool or meat (OxfordDictionaries.com).

M.E., from O.E. sceap; related to O.Frisian skep, O.Saxon scap, O.H.G. scaf, Ger. Schaf.

Gusfand, guspand, from Mid.Pers. gôspand "cattle in general," especially "sheep, goats," as distinguished from horses and cows, Av. gaospənta- "sanctified, consecrated cow," from gao-, → cow, + spənta- "sanctfied, holy," → holiday.

1) General: A relatively thin external form covering a hollow space.
2) The hard exterior of an egg; a hard outer covering of an animal, such as a mollusk.
3) Physics: → electron shell.
4) → seashell.
5) Astro.: → shell burning; → shell galaxy; → shell star; → shellular rotation; → SNR shell.

M.E.; from O.E. scell, sciell; cognate with Dutch schil "peel, skin," O.Norse skel "shell," from PIE root *(s)ker "to cut," → bark.

Pusté "shell," from pust "skin;" Mid.Pers. pôst "skin;" O.Pers. pavastā- "thin clay envelope used to protect unbaked clay tablets;" Av. pastô-, in pastô.fraθanhəm "of the breadth of the skin;" Skt. pavásta- "cover," Proto-Indo-Iranian *pauastā- "cloth."
Pukel, from (Nahâvand, Hamadân, Ilâm) pukel "egg shell," (Kurd.) tukel, probably (prefixed) from PIE root *(s)ker- "to cut," → bark, → scalp.

The nuclear reactions in a shell around a star's core that continue after the fuel in the core itself has been exhausted. As the fuel is progressively exhausted, the shell moves outward until it enters regions too cool for the reactions to continue. For example, after the exhaustion of hydrogen in the core, helium burning might take place in the core with a shell of hydrogen burning surrounding it. Stars may have more than one region of shell burning during their stellar evolution, each shell with its own nuclear reactions. → hydrogen shell burning; → helium shell burning.

→ shell; → burning.

An elliptical galaxy that is surrounded by thin shells of stars which are thought to have been ejected during a galaxy merger. Shell galaxies are different from ring galaxies in that the shells are much further away from the galaxy's centre and much fainter than the rings. Spectroscopy of the stars in the shell show that they are old whereas the stars in a ring galaxy are young.

→ shell; → galaxy.

A main-sequence star, usually of spectral class B to F, whose spectrum shows bright emission lines superimposed on the normal absorption lines. The emission spectrum is explained by the presence of a circumstellar shell of gas surrounding the star at the equator. Shell stars are fast rotators.

→ shell; → star.

A rotation mode in which internal rotation of a star depends essentially on depth and little on latitude: Ω(r,θ) = Ω(r), where r is the mean distance to the stellar center of the considered level surface (or → isobar). This particular mode was introduced by J.-P. Zahn (1992, A&A 265, 115) to simplify the treatment of rotational → mixing, but also on more physical grounds. Indeed differential rotation tends to be smoothed out in latitude through → shear turbulence. See also → von Zeipel theorem; → meridional circulation .

Shellular, the structure of this term is not clear; it may be a combination of → shell (referring to star's assumed division in differentially rotating concentric shells) + (circ)ular, → circular. The first bibliographic occurrence of shellular is seemingly in Ghosal & Spiegel (1991, On the Thermonuclear Convection: I. Shellular Instability, Geophys. Astrophys. Fluid Dyn. 61, 161). However, surprisingly the term appears only in the title, and nowhere in the body of the article; → rotation.

Carxeš, → rotation; puste-yi, adj. of pusté, → shell.

A person who takes care of sheep; a pastor. → shepherd moon.

From M.E. shepherde; O.E. sceaphierde, from sceap "sheep" + hierde "herder," from heord "a herd;" cf. M.L.G., M.Du. schaphirde, M.H.G. schafhirte, Ger. dial. schafhirt.

Cupân "shepherd," variants šobân, šabân; Mid.Pers. šubân, from šu + -bân. The first component from Av. pasu-, fšu- "sheep;" Mid.Pers. pâh, pasvīk "cattle;" Laki and Tâti pas "sheep;" Kurd. pez/paz; Ossetain (Digor.) fus, (Iron.) fys; Zazaki pes "small cattle;" Lâri pah; Qasrâni cu; Sogd. psw "cattle, sheep;" cf. Skt. paśu- "cattle;" L. pecu "flock, farm animals, cattle," pecunia "money, property;" Goth. faihu "money, fortune;" O.E. feoh "cattle, money;" Ger. Vieh "cattle;" Lith. pekus "cattle;" PIE base *peku- "cattle." The second component -pân/-bân a suffix denoting "keeper, guard," sometimes forming agent nouns or indicating relation, → host.

A → natural satellite in orbit near the edge of a → planetary ring, whose → gravitational force on the ring particles strongly controls the distribution of material within the ring, creating ringlets and density waves within the ring and sharp edges at ring boundaries. Examples include → Saturn's → Prometheus and → Pandora, which shepherd the narrow outer → F ring and the → Uranus satellites → Cordelia and → Ophelia and the epsilon ring. The faster-moving inside satellite accelerates the inner ring particles as it passes them, causing them to spiral out to larger orbits. At the same time the slower-moving outer satellite decelerates the outer ring particles as they pass by, causing them to spiral inward. The result is a narrow, well-defined ring.

→ shepherd; → moon.

1) A broad piece of armor carried on the arm as a defense against swords, arrows, etc.
2) A person or thing that protects or defends. → heat shield; → ozone shield; → self-shielding; → shielding effect.

M.E. shelde, from O.E. scield, scild, related to sciell "seashell, eggshell;" cf. Du. schild, Ger. Schild, Goth. skildus; PIE base *(s)kel- "to cut."

Separ "shield," from Mid.Pers. spar "shield;" cf. Skt. phalaka- "board, lath, leaf, shield," phálati "(he) splits;" Gk. aspalon "skin, hide," spolas "flayed skin," sphalassein "to cleave, to disrupt;" O.H.G. spaltan "to split;" Goth. spilda "board;" PIE base *(s)p(h)el- "to split, to break off."

The decrease in attraction between an electron and the nucleus in any atom with more than one → electron shell. The repulsion forces from other electrons in shells cause the net force on electrons in outer shells to be significantly smaller in magnitude. Also known as → screening effect.

→ shield; → effect;

A change in place or position, in particular a change in wavelength, causing a movement of a spectral band or line. → redshift; → blueshift.

Shift, M.E., from O.E. sciftan "to divide, arrange"; akin to O.N. skipa "to arrange, assign."

Kib "shift" from kibidan "to shift, displace, turn on one side," kibidé "displaced, turned on one side."

→ tibia.

→ tibia

Doroštney, literally "big reed," from dorošt, → macro-, + ney "reed, cane."

1) To emit rays of light.
2) Brightness caused by the emission of light.

M.E. s(c)hinen (v.); O.E. scinan "shed light, be radiant;" cf. M.H.G. schinen, O.H.G. skinan; Du. schijnen; Ger. scheinen; Gothic skeinan "to shine, appear;" PIE base *skai- "bright;" cf. Mod.Pers. sâyé "shadow;" Mid.Pers. sâyak "shadow;" Av. a-saya- "throwing no shadow;" Skt. chāya- "shadow;" Gk. skia "shade;" Rus. sijat' "to shine."

Tâbidan, tâb, → radiate; foruq, → gegenschein.

A sharp change in the properties of a gas (density, pressure, temperature).

Shock "sudden blow," from M.Fr. choc "violent attack," from O.Fr. choquer "to strike against, clash;" cf. Du. schokken "to shake, jolt, jerk."

Toš, from Tabari toš "violent blow," batoštən "to strike suddenly," Kurd. tuš "collision," maybe related to Pers. tuš "strength, vigor;" Av. təviši- "strength," tavah- "power;" O.Pers. tauman- "power, strength," tunuvant- "powerful," from tav- "to have power, to be strong, to be able" (related to tavân "power, strength," tavânestan "to be powerful, able;" variants tâv, tâb "power"); cf. Skt. tu- "to be strong, to have authority," tavas-, tavisa- "strong, energetic," tavisi- "power, strength."
Šok, loan from Fr., as above.

A burst of very bright → ultraviolet or → soft X-ray radiation expected to occur in → core-collapse supernovae at the instant when the → supernova shock breaks out of the stellar surface. During the collapse of the progenitor → massive star, the density in the iron core increases drastically. Once the core material reaches → nuclear density, the core rebounds generating a → shock wave that moves outward through the star. When the shock reaches the outermost layers, it ejects them out into space at → relativistic speeds.

→ shock; breakout "a forceful escape from being confined or restrained," from break, from M.E. breken, O.E. brecan (cf. Du. breken, O.H.G. brehhan, Ger. brechen), from PIE base *bhreg- "to break" (see also → fraction) + → out.

Borunzani "emergence, evasion," from borun, → out, + zani verbal noun of zadan "to strike, beat," from Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *g^when- "to strike, kill."

Any of a series of rings/disks that are formed in a jet flow exhausting a → nozzle when there is a huge difference between the exit pressure and the ambient pressure. At sea level, the exhaust pressure might be lower than the thick atmosphere. In contrast, at very high altitudes, the exhaust pressure might be higher than the thin atmosphere. Shock diamonds can appear just as a rocket is taking off, or at high altitudes when it shifts into → supersonic speed. Shock diamonds are also known as Mach diamonds, → Mach disks, Mach rings, doughnut tails, or thrust diamonds.

→ shock; → diamond.

The boundary over which the physical conditions undergo an abrupt change because of a → shock wave.

→ shock; → front.