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

1) (v.) To sweep a surface with a beam of light or electrons in order to reproduce or transmit a picture.
In radar, to sweep an airspace or region with a succession of directed beams from a radar aerial system.
2) (n.) An act or instance of scanning. The image or display so obtained.

M.E. scannen, from L.L. scandere "to read or mark so as to show metrical structure," originally, in classical L., "to climb" (the connecting notion is of the rising and falling rhythm of poetry), from PIE *skand- "to spring, leap" (cf. Skt. skandati "he jumps;" Gk. skandalon "a snare, trap, stumbling block;" O.Ir. scendim "I jump").

Rajrub, literally "sweeping along rows," from raj "row, line" + rub "to sweep." The first component raj, variants raž, rak, râk, rezg (Lori), ris, risé, radé, rasté, râsté, related to râst "right, true; just, upright, straight," → row, → right. The second component rub stem of rubidan, ruftan "to sweep," related to robudan "to rub, carry off;" Mid.Pers. rôb- "to rub, sweep, attract;" Av. urūpaiieinti "to cause racking pain(?);" cf. Skt. rop- "to suffer from abdominal pain," rurupas "to cause violent pain," ropaná- "causing racking pain," rópi- "racking pain;" L. rumpere "to break;" O.E. reofan "to break, tear."

Any device for exposing an image on film, a sensitized plate, etc., by tracing light along a series of many closely spaced parallel lines.

Agent noun of → scan.

The process of analyzing or synthetizing successively the light values of the elements making up a picture area, according to a pre-determined method.

Verbal noun of → scan.

A → sundial consisting of an inverted half sphere and a central vertical → gnomon used by ancient Greeks. See also → Eratosthenes experiment.

Gk. skaphe "boat, skiff; a bowl."

A flat triangular bone a pair of which form the back part of the shoulder. Commonly known as → shoulder blade.

L. scapula "shoulder."

Šâné, Mid.Pers. šânag "shoulder-blade."
Ketf, loan from Ar. kataf "shoulder."

Geology: A line of cliffs produced by faulting, erosion, or landslides. → cliff.

From It. scarpa.

Tondé "a steep slope of a mountain," from tond "swift, rapid, brisk; fierce, severe" (Mid.Pers. tund "sharp, violent;" Sogdian tund "violent;" cf. Skt. tod- "to thrust, give a push," tudáti "he thrusts;" L. tundere "to thrust, to hit" (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere "to thrust or bore through;" PIE base *(s)teud- "to thrust, to beat"); cf. dialectal Anzali tin, Laki den, Tâleši teš "steep rock."

1) To cause → electromagnetic waves or a → beam of → particles to be irregularly → deflected, → dispersed, or → reflected, or be turned aside in the process of → scattering.
2) The act of → scattering; something that is → scattered.

M.E. scateren, schateren "to disperse, break up, destroy;" cf. M.Du. schaderen "to scatter."

Parâkandan "to scatter, to disperse;" Mid.Pers. parakandan "to scatter" (cf. apakandan "to throw"), from Proto-Iranian *pari-kan-, from *pari, *par- "around" (cf. Pers. pirâ-, variant par- "around, about," from Mid.Pers. pêrâ; O.Pers. pariy "around, about," Av. pairi "around, over," per- "to pass over, beyond;" cf. Skt. pari; PIE base *per- "through, across, beyond;" cf. Gk. peri "around, about, beyond;" L. per "through") + *kan- "to throw, place, put" (cf. Pers. afgandan "to throw; to lay, place;" kandan "to dig; to extract;" Mid.Pers. kan-, kandan "to dig;" O.Pers. kan- "to dig," akaniya- "it was dug;" Av. kan- "to dig," uskən- "to dig out;" cf. Skt. khan- "to dig," khanati "he digs," kha- "cavity, hollow, cave, aperture").

1) Occurring or distributed over widely spaced and irregular intervals in time or space.
2) The quality of a particle that has undergone → scattering.

Past participle of → scatter.

A → particle that causes → scattering of another particle through interaction with it.

→ scatter; → -er.

The process in which the direction of motion of → particles or → waves is changed randomly because of their → interactions (→ collisions) with other particles of the → medium transversed.
Two parameters govern scattering: 1) the wavelength (λ) of the incident radiation, and 2) the size of the scattering particle (r), usually expressed as the nondimensional size parameter, x = 2πr / λ. The size parameter defines three types of scattering:
1) x much less than 1 (or r much smaller than λ), → Rayleigh scattering;
2) x ~ 1 (or rλ), → Mie scattering; and
3) x much larger than 1 (or r much larger than λ), → geometric scattering.
See also: → atmospheric scattering, → backscattering, → Brillouin scattering, → coherent scattering, → Compton scattering, → elastic scattering, → forward scattering, → last scattering, → last scattering surface, → multiple scattering, → noncoherent scattering, → quasi-single-scattering approximation, → Raman scattering, → scattering angle, → scattering coefficient, → scattering of stars, → selective scattering, → single scattering, → spin-flip scattering, → surface of last scattering, → Thomson scattering.
Related terms: → diffraction; → diffusion; → dispersion; → distribution.

Verbal noun of → scatter.

The angle between the → incident radiation on a → particle (such as a water droplet in a rainbow) and the scattered radiation (such as the light ray leaving the droplet). Scattering angle is a function of → impact parameter. In other words, The angle along which the change of direction has taken place, irrespective whether radiation is scattered by particles or reflected (refracted) by a surface.

→ scattering; → angle.

The fraction of light scattered per unit distance in a medium.

→ scattering; → coefficient.

The progressive increase of random motions of → disk stars with increasing stellar → ages. While some initial random motion seems likely in the disturbed conditions of disks when the oldest stars formed, the observation is generally attributed to scattering processes. Both massive gas → clumps and → spiral waves are considered as scattering agents (J. A. Sellwood & J. J. Binney, 2002, astro-ph/0203510 and references therein).

→ scattering; → star.

During the → main sequence stage, a star burns the hydrogen in its core and transforms it into helium. When the helium mass amounts to about 10% of the initial stellar mass, the star can no longer maintain the → hydrostatic equilibrium in its core; the star increases its volume and leaves the main sequence in order to become a → red giant.

Named after the Brazilian astrophysicist Mario Schönberg (1914-1990) and Subramahmanyan Chandrasekhar, → Chandrasekhar limit, who were the first to point out this limit and derive it (1942, ApJ 96, 161).

The second-brightest star in the constellation → Pegasus. It is a giant star of spectral type M2.5 II-III whose magnitude varies between 2.3 and 2.7.

Scheat, from Ar. as-sâq "leg," erroneously taken from the Ar. name of δ Aquarii as-sâq al-sâkib al-ma' (الساق الساکب‌الماء) "the leg of the water-bearer."

Asb-šâné, literally "the Horse's Shoulder," from asb→ horse + šâné "shoulder" (Lori šona, Kurd. šân, Gilaki cân, con), maybe related to Skt. skandhá- "shoulder, trunk of tree, bulk" (Pali khandha-, Ashkun kándä, Bashkarih kân, Tôrwâldi kan "shoulder"), from skand- "to jump, leap, spring out," skandati "he jumps;" cf. L. scandere "to climb."

A mathematical expression that describes the → luminosity function of galaxies. The function correctly reflects the facts that the luminosity function decreases with increasing luminosity and that the decrease is particularly marked at high luminosities. It is expressed as: φ(L) = φ^*(L/L^*)^α exp (-L/L^*), which has two parts and three parameters: φ^* is an empirically determined amplitude, α is an empirically derived exponent, and L^* is a characteristic luminosity which separates the low and high luminosity parts. For small luminosities (L much smaller than L^*) the Schechter function approaches a power law, while at high luminosities (L much larger than L^*) the frequency of galaxies drops exponentially. φ^*, L^*, and the faint-end slope α depend on the observed wavelength range, on the → redshift, and on the environment where the galaxies are observed.

Named after the American astronomer Paul Schechter (1948-), who proposed the function in 1976 (ApJ 203, 297); → function.

A power-law relation between → star formation rate (SFR) and a corresponding measure of gas density. For external galaxies it is usually expressed in terms of the observable surface density of gas (Σ_gas): SFR ∝ Σ_gasⁿ. The exponent n is determined to be 1.4 ± 0.15 (Kennicutt 1998, ApJ 498, 541). The validity of the Schmidt law has been tested in dozens of empirical studies. The Schmidt law provides a tight parametrization of the global star formation law, extending over several orders of magnitude in SFR and gas density.

Named after Maarten Schmidt (1929-), a dutch-born American astronomer, who also discovered the first → quasar (3C 273) in 1963.

A telescope with a spherical concave primary mirror in which the aberration produced by the spherical mirror is compensated for by a thin correcting lens placed at the opening of the telescope tube. Its very wide-field performance makes it suitable for surveys.

Named after Bernhard Woldemar Schmidt (1879-1935), a German optician of Estonian origin, who invented the telescope in 1930; → telescope.

A mixture of the → Cassegrain telescope with a very short → focal length and of a Schmidt design (due to the presence of the → corrective plate), used mainly in → amateur astronomy. The main advantage of this telescope is its compact design. However, Schmidt-Cassegrain telescopes produce fainter images with less contrast than other telescope designs with similar → aperture sizes. This is due to the comparatively large → secondary mirror required to reflect the light back the → eyepiece.

→ Schmidt telescope; → Cassegrain telescope.

Same as the → Schmidt law.

Named after the American astrophysicists Maarten Schmidt (1929-), the pioneer of research in this field, and Robert C. Kennicutt, Jr. (1951-), who developed the study; → relation.