An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 13048 Search : far
Sextans
  ششکان   
Šešakân

Fr.: Sextant   

The Sextant. An inconspicuous constellation located on the celestial equator at 10h 20m, 0° declination. Its brightest star, Alpha Sextantis is of 4th magnitude. It was introduced in the 17th century by Johannes Hevelius (1611-1687). Abbreviation: Sex; genitive: Sextantis.

The name is L. for → sextant, an instrument that Hevelius made frequent use of in his observations.

sextant
  ششکان   
šešakân

Fr.: sextant   

An instrument used mainly in nautical astronomy to determine the angular distances of celestial bodies above the horizon. The sextant consists of a 60° graduated arc, or limb, a small telescope, and two mirrors. Only half of one of the mirrors, the horizon glass, is silvered and, like the telescope, it is fastened to the frame supporting the limb. The other mirror, the index mirror, moves with an index arm pivoted at the center of the arc. The index arm is equipped with a → vernier which moves along the limb. An object in direction S can be observed in the telescope through the un-silvered portion of the horizon glass. By moving the index arm, the second object S' is made to coincide with S in the telescope. According to the law of reflection, the angle between S and S' is double the angle between the mirrors. The angular distance between the objects can therefore be obtained from the measurement of angles between the planes of the mirrors.

From Mod.L. sextans, from L. sextans "a sixth," from sexsix.

Šešakân, from šešak "a sixth," from šeš, → six + -ak, contraction of yak "one," (Mid.Pers. êwak; Proto-Iranian *aiua-ka-; O.Pers. aiva- "one, alone;" Av. aēuua- "one, alone" (cf. Skt. éka- "one, alone, single;" Gk. oios "alone, lonely;" L. unus "one;" E. one) + -ân nuance suffix.

sextet
  شش‌تایه   
šeštâyé

Fr.: sextet   

Any group or set of six. → Seyfert's sextet.

From Latinized sestet, from It. sestetto, diminutive of sesto "sixth," from L. sextus "sixth," from sex, → six.

Šeštâyé, from šeš, → six, + "fold, plait, ply; piece, part" (Mid.Pers. tâg "piece, part") + -(y)é nuance suffix.

sextuplet
  ششتایی   
šeštâyi

Fr.: sextuplet   

A group or combination of six objects, such as the → Mizar and the → Castor star systems.

From sextuple, from L. sext(us) "sixth," → six, + et

Seyfert galaxy
  کهکشان ِ سیفرت   
kahkešân-e Seyfert

Fr.: galaxie de Seyfert   

A member of an important class of → active galaxies which are characterized by the presence of an intensely bright nucleus in the optical wavelengths (109-1012Lsun) displaying emission spectral lines. The presence of these emission features, which are not seen in the spectra of normal galaxies, indicates a very high degree of ionization. Moreover, the nucleus radiates → non-thermal  → continuum emission extending over the whole electromagnetic spectrum. It is thought that a → massive black hole in the nucleus of a galaxy accretes gas (→ accretion) from its surrounding environment to power Seyfert galaxies. These galaxies are divided into two types according to the width of their spectral lines. Type 1 Seyfert (Sy 1) galaxies have very broad emission lines (103- 104 km s-1), while Type 2 Seyferts (Sy 2) show relatively narrow lines (several hundred km s-1). These spectral differences may be the result of viewing the nucleus from different angles. A Type 2 Seyfert galaxy may be a mostly edge-on view of matter spiraling in toward the supermassive black hole, whereas a Type 1 Seyfert provides a more pole-on view, allowing us to see the more turbulent region around the black hole.

Named after Carl Keenan Seyfert (1911-1960), the American astronomer who first identified this type of galaxies in 1943; → galaxy.

Seyfert's sextet
  شش‌تایه‌ی ِ سیفرت   
Šeštâye-ye Seyfert

Fr.: Sextette de Seyfert   

A group of galaxies about 190 million → light-years away in the head portion of the constellation → Serpens. The group appears to contain six members, but actually contains only four → interacting galaxies. A face-on → spiral galaxy lies in the distant background and appears only by chance aligned with the main group. Also, a prominent condensation is likely not a separate galaxy, but a → tidal tail of stars flung out by the galaxies' gravitational interactions. The interacting galaxies are tightly packed into a region around 100,000 light-years across, comparable to the size of our own Milky Way galaxy, making this one of the densest known galaxy groups.

Discovered by the American astronomer Carl Keenan Seyfert (1911-1960) using photographic plates made at the Barnard Observatory of Vanderbilt University. → sextet.

Sgr A*
     
Sgr A*

Fr.: Sgr A*   

The object identified as the Galactic → supermassive black hole.

Sagittarius A (Sgr A).

Sgr A* cluster
  خوشه‌ی ِ *Sgr A   
xuše-ye Sgr A*

Fr.: amas Sgr A*   

Same as → S cluster.

Sgr A*; → cluster.

Sh2-279
     
Sh2-279

Fr.: Sh2-279   

A large → H II region in the north part of → Orion's Sword composed of reflection and emission components ( → reflection nebula, → emission nebula). It includes NGC 1977, NGC 1975, and NGC 1973, separated from each other by a → dark nebula which resembles a running man, as well as the → open cluster NGC 1981. NGC 1977, the designation some sources use to describe the entire complex, is the largest and brightest nebulous component first described by Herschel in 1786. The nebula is approximately 40 arcmin in apparent diameter, and 1,500 → light-years distant.

Nebula number 279 in the second edition of the → Sharpless catalog.

Shack-Hartmann wavefront sensor
  حسگر ِ پیشان ِ موج ِ شک-هارتمان   
hessgar-e pišân-e mowj-e Shack-Hartmann

Fr.: analyseur de front d'onde   

An optical device, a modern version of the → Hartmann test, used for analyzing the wavefront of light. Theses sensors can be used to characterize the performance of optical systems. Moreover, they are increasingly used in real-time applications, such as → adaptive optics to remove the wavefront distortion before creating an image. It consists of a microlens array placed in front of a CCD array. A planar wavefront that is transmitted through a microlens array and imaged on the CCD array will form a regular pattern of bright spots. If, however, the wavefront is distorted, the light imaged on the CCD will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wavefront that was incident on the microlens array.

Named after the German astronomer Johannes Hartmann (1865-1936), who first developed the method, and R. V. Shack, who in the late 1960s replaced the screen by a microlens array; → wavefront; → sensor.

shade
  سیوان   
sivân

Fr.: ombre   

1) The comparative darkness caused by the interception or screening of rays of light from an object, place, or area.
2) A place or an area of comparative darkness, as one sheltered from the sun (Dictionary.com). See also → shadow.

M.E. schade; O.E. scead "partial darkness; shelter," → shadow.

Sivân, from Kurd. sayvân "shadow, shade," variants si, sâ, sâyé, → shadow.

shadow
  سایه   
sâyé (#)

Fr.: ombre   

A dark patch formed by a body which obstructs rays of light.

M.E. sch(e)adew(e), schadow, shadw(e), O.E. sceadwe, sceaduwe, sceadu "shade, shadow, darkness;" cf. O.S. skado, M.Du. scade, Du. schaduw, O.H.G. scato, Ger. Schatten, Goth. skadus; from PIE base *skot- "dark, shade."

Sâyé "shadow," from Mid.Pers. sâyak "shadow;" Av. a-saya- "throwing no shadow;" Skt. chāya- "shadow;" Gk. skia "shade;" Rus. sijat' "to shine;" M.H.G. schinen, O.H.G. skinan, Ger. Schein "glow, shine;" PIE base *skai- "bright."

shadow bands
  نوارهای ِ سایه، باندهای ِ ~   
navârhâ-ye sâyé, bândhâ-ye ~

Fr.: ombres volantes   

Faint wavy lines of alternating light and dark that sometimes can be seen on flat, light-colored surfaces just before and just after a total solar eclipse. The phenomenon results from sunlight distortion by irregularities in the Earth's atmosphere.

shadow; → band.

shadow cone
  مخروط سایه   
maxrut-e sâyé

Fr.: cône d'ombre   

A cone-shaped shadow cast by Earth or the Moon pointing away from the Sun. The dark inner portion of the shadow cone is called the → umbra. The lighter outer portion of the shadow is called the → penumbra. Its extension is called the → antumbra.

shadow; → cone.

shale
  اردوال   
ardavâl (#)

Fr.: schiste, schiste argileux   

A fissile rock composed mostly of layers of clay-like, fine-grained → sediments. Shale is the most frequently occurring → sedimentary rock.

Probably from obsolete or dialect shale "scale, shell," from M.E., from O.E. scealu, → rock.

Ardavâl "shale," in the dialectal Mod.Pers. of Golpâyegân, Arâk, Xonsâr, etc.

shallow
  نژل   
nažal

Fr.: peu profond   

Of little depth; not deep.

M.E. schalowe, akin to O.E. sceald "shallow."

Nažal, from negation prefix na-, → non-, + žal "deep," variant of jal, jol, jul, → deep.

shallow angle
  زاویه‌ی ِ نژل   
zâviye-ye nažal

Fr.: angle faible   

Low angle, → grazing incidence.

shallow; → angle.

shank
  ساق، پاچه   
sâq (#), pâcé (#)

Fr.: jambe, jarret   

The part of the → leg between the → knee and the → ankle in humans.

O.E. sceanca "leg, shank, shinbone;" cf. Ger. schenkel "shank, leg," Dan., Swed. skank "leg;" maybe somehow related to Pers. leng, → leg.

Sâq "the leg from the ankle to the knee; the stem of a tree," maybe a variant of šâx "a branch, bough; a horn," or loan from Ar.

Shannon entropy
  درگاشت ِ شانون   
dargâšt-e Shannon

Fr.: entropie de Shannon   

information entropy.

Claude Elwood Shannon (1916-2001), an American mathematician and pioneer of → information theory; → entropy.

Shannon's sampling theorem
  فربین ِ نمونان‌گیری ِ شانون   
farbin-e nemunân-giri-ye Shannon

Fr.: théorème d'échantillonnage de Shannon   

Same as → sampling theorem.

Shannon entropy; → sampling; → theorem.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer AGB air Alf Alg all alp alt AM amo ana And ang ani ano Ant Ant apa apo app app Ara Arc ari Arr ash ass ast ast asy atm ato att aut ave axi Bab bal Bal bar bar bea Bek Bes bia Big bin bin bip biv bla bli blu Boh Bol Bos bou bra bri bro buo cal cal can cap car Car cat cat CCD Cen cen CH cha cha che Che chr cir cir cit cla clo clo clu Coa coe coh col col col com com com com com com com com Com con con con con con con con con con con con con Cop Cor cor cor cos cos cou cou Cow cre cri cro cry cur cya Cyg dan dar dat de- deb dec dec ded def deg del dem den dep des det dev dia dif dif dih dio Dir dis dis dis dis dis dis DO don dou dow dro dur dwa dyn Dys ear ebb ecl edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ esc eth Eur Eve exa exc exe exi exp exp ext ext ext fac fal far fed Fer fer fie fin fir fis fla flo flu fol for for fou fra fre Fre fro fut G-t gal gal gam gas Gau Gem gen geo geo geo gia Gli Gol gra gra gra gra gre gri gui H I Hag hal har hat He- hea hel Hel her Hes hie hig his hom hor hot Hub Hug hur hyd hyd hyg hyp ice ide ima Ima imp imp inc inc ind ine inf inf inf ing inn ins ins int int int int int int int int inv Io ion iro isl iso iso Jac jet jud jur Kel Kep kil Klo Kui Lag lam Lap Lar lat law lea len lep Lib lig lim lin lin Lio lit loc LOF lon Lor low lum lun Lup Lyo mac mag mag mag mag mag mai man Mar mas mas mat Max mea mec Meg Mer Mer met met Met mic Mid Mil min Mir mit mod mod mol mon Mor mou mul mul mys nan Nat nau nec neo neu nev New NGC no nom non non nor not nuc nuc num nut obj obs obs occ ocu oft ome Oor ope opp opt opt orb ord ori ort osc out ove oxi pai pan par par par par pas pea pen per per per per Per per pha phi pho pho pho phy pio Pla pla pla pla Pla plu Poi pol pol pol poo pos pos pot pra pre pre pre pre pri pri pro pro pro pro pro Pro pro pse pul pur qua qua qua qua que rac rad rad rad rad rad rad ran rar ray rea rea rec rec red red ref ref reg rel rel rel ren res res res res ret rev Ric rig rin roc roo rot rot Rus Sac sal sat sca sca Sch sci Scu sec sec Sed sel Sel sen ser Sex Sha she sho sid sig sil sim sin siz sla Sma sno sof sol sol sol sol sou sou spa spa spe spe spe sph spi spi spr squ sta sta sta sta ste ste ste Sto Str str str sub sub suc sun sup sup sup sup sur swa syn syn tab tar tek tem ter tes the the the the Tho thr tid tim Tis Too Tor tra tra Tra tra tra tri tri tru Tul tur two Typ ult un- und uni uni unk upp Urc utt val var vec vel ver vib vio vir vis voi vor wan wat wav wax wea Wei whi Wil win WN9 wor X-r yel you zer zod > >>