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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 1286
sexagesimal
  شست-شستی   
šast-šasti (#)

Fr.: sexagésimal   

Relating to, or based on, the number 60.

From M.L. sexagesimalis, from L. sexagesimus "sixtieth," from sexaginta "sixty."

Šast-šasti, from Šast, → sixty.

sexagesimal system
  راژمان ِ شست-شستی   
râžmân-e šast-šasti

Fr.: système sexagésimal   

A number system whose base is 60. It originated with the ancient Sumerians around 2000 B.C., was transmitted to the Babylonians, and is still used in modified form for measuring time, angles, and geographic coordinates.

sexagesimal; → system.

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.

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.

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.

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.

Shapiro time delay
  درنگ ِ شپیرو   
derang-e Shapiro

Fr.: effet Shapiro   

A → general relativity effect whereby an → electromagnetic signal passing near a massive object takes, due to the curved → space-time, a slightly longer time to travel to a target than it would if the mass of the object were not present. The Shapiro time delay is one of the four classic solar system tests of general relativity. Radar reflections from → Mercury and → Mars are consistent with general relativity to an accuracy of about 5%. The Shapiro time delay is a significant contributor in → gravitational lens systems.

Irwin I. Shapiro, an American astrophysicist; → time; → delay.

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