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

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.

Low angle, → grazing incidence.

→ shallow; → angle.

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.

→ information entropy.

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

Same as → sampling theorem.

→ Shannon entropy; → sampling; → theorem.

The appearance of something in terms of its arrangement in space, especially its outline.

M.E., from O.E. sceapen, gescapen, p.p. of scieppan; cognate with O.H.G. skepfen "to shape."

Šekl, → figure; dise, → form.

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.

Same as the → Shapley supercluster.

→ Shapley's wing; → concentration

The richest → supercluster of galaxies in the nearby → Universe at a → redshift going from z ~0.03 to z ~0.05 (680 million → light-years), and extending over several square degrees on the plane of the sky. It lies behind the → Centaurus supercluster. Also called the Shapley concentration, it is made up of 25 → galaxy clusters with a total mass of about 10¹⁶→ solar masses. At the core of the Shapley supercluster is a remarkable complex formed by several rich clusters of galaxies from the → Abell catalog; the central and most massive of them is A3558.

→ Shapley's wing; → supercluster

A large cloud of faint stars extending eastward from the → Small Magellanic Cloud to the → Large Magellanic Cloud. The wing is in fact the tail of a much larger → neutral hydrogen structure linking the SMC to the LMC. Models and observations suggest that the structure known as the → Magellanic Stream results from the Clouds' interaction with each other and the Milky Way. Several works support the finding that the SMC wing is pointing toward the LMC, and is therefore closer to us than the SMC bar.

Named after the American astronomer Harlow Shapley (1885-1972), who discovered this structure (1940, Harvard Bull., 914, 8); → wing.

A catalog of 1,249 galaxies, brighter than the 13th magnitude, published in 1932. A revised version was published by A.R. Sandage and G. A. Tammann in 1981.

By the American astronomer Harlow Shapley (1885-1972) and the American woman astronomer Adelaide Ames (1900-1932), who died in a drowning accident; → catalog.

→ linear astrolabe.

Named after the Iranian mathematician and astronomer Sharafeddin Tusi (c1135-1213), who invented the instrument. Not to be confused with Nasireddin Tusi (1201-1274), → Nasireddin couple; → staff.

1a) The full or proper portion or part allotted or belonging to or contributed or owed by an individual or group.
1b) One of the equal fractional parts into which the capital stock of a joint-stock company or a corporation is divided.
2a) To divide and distribute in shares; apportion.
2b) To use, participate in, enjoy, receive, etc., jointly (Dictionary.com).

M.E., from O.E. scearu "a cutting, shearing; a part or division," related to sceran "to cut;" O.H.G. scara "troop, share of forced labor," Ger. Schar "troop, band," properly "a part of an army," O.N. skör "rim;" from PIE root *(s)ker- "to cut."

Bâš, from Kurd. (Sorani) baš "share, part;" variant of baxš "share, portion;" baxšidan "to divide," → division; bâž "tribute, toll, impost," → distribute.

1) Having a thin cutting edge or a fine point.
2) Of an image, clearly defined; distinct. → sharp image.

M.E.; O.E. scearp "cutting, keen, sharp;" cf. Du. scherp, Ger. scharf "sharp;" PIE base *(s)ker- "to cut."

Tiz "sharp," variants tež, tej, tij, tiq, tik, tig; Mid.Pers. tigr, têz, têž "sharp;" O.Pers. tigra- "pointed," tigra.xauda- "pointed helmet (epithet of Scythians);" Av. tiγra- "pointed," tiγray- "arrow," tiži.arštay- "with the pointed spear;" cf. Skt. tikta- "sharp, pungent, bitter," tejas- "sharpness, edge, point or top of a flame;" PIE base *st(e)ig- "to stick; pointed." Cognates in other IE languages: Gk. stizein "to prick, puncture," stigma "mark made by a pointed instrument;" L. in-stigare "to goad;" O.H.G. stehhan; Ger. stechen "to stab, prick;" Du. stecken; O.E. sticca "rod, twig, spoon;" E. stick.