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

A mathematical formula yielding an approximate value for → factorial n, when n is large: n! ≅ (2πn)^1/2nⁿe^-n, where e is the base of → natural logarithm.

Named after James Stirling (1692-1770), a Scottish mathematician; → approximation.

Involving or containing a random variable or variables. A stochastic variable is neither completely determined nor completely random. A system containing one or more stochastic variables is probabilistically determined.

From Gk. stokhastikos "able to guess, conjecturing," from stokhazesthai "to aim at, guess," from stokhos "a guess, target," literally "pointed stake."

Kâturgin, from kâtur, kâturé, → random + -gin, adj. suffix, contraction of âgin "filled."

The mechanism arising from turbulent convection in the → convective zone of stars, which is responsible for the driving of stellar → pulsation modes. In stars cooler than typically ~ 7 500 K (→ F-type stars and cooler), the stochastic excitation occurs in the convection envelope. In massive stars, it may develop either in the → convective core or in the convective layer beneath the → photosphere. Recent studies suggest that in → Be stars stochastic excitation takes place in the convective core. The stochastic waves can transport → angular momentum from the core to the surface. Fast rotation, as in Be stars, amplifies the stochastic excitation.

→ stochastic; → mode.

Any process involving a sequence of random variables. The future evolution of a stochastic process is therefore described by probability distributions.

→ stochastic; → process.

A mechanism that could be responsible for global → spiral structure in galaxies either by itself or in conjunction with spiral → density waves. In this mechanism, star formation is caused by → supernova-induced → shocks which compress the → interstellar medium. The → massive stars thus formed may, when they explode, induce further → star formation. If conditions are right, the process becomes self-propagating, resulting in agglomerations of young stars and hot gas which are stretched into spiral shaped features by → differential rotation. Merging of small agglomerations into larger ones may then produce large-scale spiral structure over the entire galaxy. The SSPSF model, first suggested by Mueller & Arnett (1976) was developed by Gerola & Seiden (1978). While the → density wave theory postulates that spiral structure is due to a global property of the galaxy, the SSPSF model examines the alternative viewpoint, namely that spiral structure may be induced by more local processes. The two mechanisms are not necessarily mutually exclusive, but they involve very different approaches to the modeling of galaxy evolution. The SSPSF gives a better fit than the density wave theory to the patchy spiral arms found in many spiral galaxies. However, it cannot explain → galactic bars.

→ stochastic; → self; → propagate; → star; → formation.

1) The statement or discussion of the first principles of any science or art (1913 Webster).
2) Logic: The doctrine of the elementary requisites of mere thought (Sir W. Hamilton; 1913 Webster).

→ stoichiometry, → -logy.

1) Of or pertaining to → stoichiometry.
2) Pertaining to or involving substances that are in the exact proportions required for a given reaction.

→ stoichiometry; → -ic.

1) The branch of chemistry that studies chemical processes within the context of the laws of definite proportions and conservation of matter and energy.
2) The study of the quantitative relationships of two or more compounds in a chemical reaction.

From Gk. stoikheion "element, component, principle," Stoikheia "elements" (the title of Euclid's great collection of Gk. mathematics); loaned in Ar. and Pers. (9-th century A.D.) as ustuqus (اسطقس); akin to stoikhos "row, line, verse," steikhein "to go, march;" cf. Skt. stighnoti "rises, steps;" O.H.G. stigan; Ger. steigen; Goth. steigan "to go up, ascend;" O.E. stigan "to climb, go;" Ger. Steig "path;" O.E. stig "narrow path;" PIE base *steigh- "to go, rise, step, walk," + → -metry.

Stoyxiyosanji, from stoyxiyo loan from Gk., as above, + -sanji, → -metry.

The unit of → viscosity in the → cgs system, cm² s^-1, equal to 10^-4 m² s^-1.

After Sir George Gabriel Stokes (1819-1903), a British mathematician and physicist, who made important contributions to fluid dynamics, optics, and mathematical physics; → Stokes law; → Stokes parameter.

For the translational motion of a spherical body moving in a → viscous fluid, the proportionality factor between the uniform flow velocity far from the sphere and the drag force, provided no-slip boundary condition and small → Reynolds numbers: f = 6πηR, where η is the Reynolds number and R radius of the sphere.

→ Stokes; → friction; → factor.

1) Fluid mechanics: At low velocities, the frictional force on a spherical body moving through a fluid at constant velocity is equal to 6πRηv, where R is the radius of the sphere, η the fluid → viscosity, and v the velocity.
2) Spectroscopy: The wavelength of → luminescence excited by radiation is always greater than that of the exciting radiation.

→ Stokes; → law.

Four parameters which are needed to fully describe the → polarization state of → electromagnetic radiation. They involve the maximum and minimum intensity, the ellipticity, and the direction of polarization. The four Stokes parameters are traditionally defined as follows:
I ≡ total intensity.
Q ≡ I₀ - I₉₀ = difference in intensities between → horizontal and → vertical  → linearly polarized components.
U ≡ I₊₄₅ - I_-45 = difference in intensities between linearly polarized components oriented at +45° and -45° (or 135°).
V ≡ I_rcp - I_lcp = difference in intensities between right and left → circularly polarized polarized components.

→ Stokes; → parameter.

The hard nonmetallic mineral or group of consolidated minerals either in mass or in a fragment of pebble or larger size. See also → rock.

O.E. stan; cf. O.N. steinn, Dan. steen, O.H.G., Ger. Stein; from PIE *stai- "stone," also "to thicken, stiffen" (cf. Skt. styayate "curdles, becomes hard;" Av. stay- "heap;" Gk. stear "fat, tallow," stia, stion "pebble").

Sang "stone, rock;" Mid.Pers. sang; O.Pers. aθanga-; Av. asenga- "stone;" PIE *aken-.

A prehistoric period during which the main material used to make tools and weapons was stone. The Stone Age is usually divided into three separate periods (Paleolithic Period, Mesolithic Period, and Neolithic Period) based on the degree of sophistication in the fashioning and use of tools. The Paleolithic time period is by far the longest, beginning some two million years ago and ending around 10,000 BC to coincide with the end of the last ice age (Pleistocene epoch).

→ stone; → age.

A meteorite composed largely of rock-forming (→ silicate) → minerals. Stony meteorites are the most abundant kind, about 95%, of all meteorites. They are divided into two groups: → chondrites and → achondrites.

→ stone; → meteorite.

Meteorites comprised of roughly equal amounts of → nickel/→ iron and → stone. They are divided into two groups: → pallasites and → mesosiderites. The stony-irons are thought to have formed at the core/mantle boundary of their parent bodies. The stony-irons account for less than 2% of all known meteorites. Also called → siderolite.

→ stony; → iron; → meteorite.

1) To hinder or prevent the passage of. → stopping power.
2) The diaphragm used in optical instruments to cut off the marginal portions of a beam of light passing through lenses. → field stop; → stop number.

M.E. stoppen (v.), O.E. -stoppian (in forstoppian "to stop up, stifle"); V.L. *stuppare "to stop or stuff with tow or oakum" (cf. It. stoppare, Fr. étouper "to stop with tow"), from L. stuppa "coarse part of flax, tow."

1) Bâzdâštan, bâzdâšt- "to stop, restrain, inhibit, coerce, detain," from bâz-, → re-, + dâštan "to have, hold, maintain, possess," → access.
2) Daricé, literally "small door; window," from dar "door," + -cé diminutive suffix. Dar "door," Mid.Pers. dar, O.Pers. duvara-, Av. dvar-, cf. Skt. dvár-, Gk. thura, L. fores, P.Gmc. *dur-, O.E. duru, E. door, Lith. dvaras "court-yard;" PIE *dhwer-/*dhwor- "door, gate."

→ occlusive consonant.

→ stop; → consonant.

Same as → focal ratio.

→ stop; → ratio.

Vâbar, → ratio; kânuni, → focal.

A quantity indicating the extent with which a substance absorbs a → charged particle passing through it. It is the energy lost by a → non-relativistic particle per unit length of its path in the substance.

→ stop; → power.