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

1) The process of connecting and preparing a software program, hardware device, or computer to function properly. Setup is a file commonly called "setup.exe" that is executed to begin installing a software program onto a computer. See also → set up.
2) Equipment designed for a particular purpose; an apparatus.
3) The fashion in which something is organized or arranged.

→ set; → up.

Barbešt, from prefix bar-, → on-.

A → cardinal number between → six and → eight.

From M.E. seoven(e), seofne, seven, O.E. seofon, cognate with M.Du. seven, Du. zeven, O.H.G. sibun, Ger. sieben, related to Pers. haft, as below, from PIE *septm "seven."

Haft, from Mid.Pers. haft, Av. hapta Skt. sapta, Gk. hepta, L. septem.

Relating to, or based on, the number 60.

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

Šast-šasti, from Šast, → sixty.

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.

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.

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 sex→ six.

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.

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, + tâ "fold, plait, ply; piece, part" (Mid.Pers. tâg "piece, part") + -(y)é nuance suffix.

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

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.

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.

The object identified as the Galactic → supermassive black hole.

→ Sagittarius A (Sgr A).

Same as → S cluster.

→ Sgr A*; → cluster.

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.

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.

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.

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."

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.

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.

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.

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.