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

A set of → differential equations describing the physical properties of stars based on two main assumptions: a star is a perfect sphere and the net force on a macroscopic mass element is zero. If the effects of rotation and magnetism are ignored, these assumptions lead to a set of five differential equations.

→ stellar; → structure; → equation.

A combining form meaning "having and dealing with three dimensions of space; solid."

From stereo a shortening of stereotype, from Fr. stéréotype (adj.) "printing by means of a solid plate of type," from Gk. stereos "solid."

Loan from Fr., as above.

A device that allows two images of the sky taken at different times to be optically superimposed so that changes in star brightness or moving objects can be detected.

→ stereo-; comparator, from L. comparare "to place together, match," from compar "alike, matching," → com-; → partial + -tor.

Ham-sanj-gar "comapartor," from ham-, → com-, + sanj stem of sanjidan "to compare" + -gar, → -or; → stereo-.

Of, relating to, or being a delineation of the form of a solid body on a plane.

→ stereography; → -ic

A graphical method of depicting three-dimensional geometrical objects in two dimensions. In a → planispheric astrolabe, it is the projection of a point of the celestial sphere onto the equatorial plane, as seen from one of the poles. The center of projection is the South pole for the northern hemisphere, and the North pole for the southern hemisphere. In this operation the projection of any circle of the sphere remains a circle on the projection plane and moreover the projection does not alter angles.

→ stereographic; → projection

The process or art of depicting solid objects on a plane surface.

→ stereo- + → -graphy

An optical instrument for viewing an overlapping pair of photographs (or perspective drawings) in order to see a three-dimensional image.

→ stereo-; → -scope.

The second major layer of Earth's atmosphere, just above the → troposphere and below the → mesosphere, extending from about 20 km to 90 km above the Earth. It is characterized by little vertical increase in temperature.

From Fr. stratosphère, literally "sphere of layers," coined by Fr. meteorologist Léon-Philippe Teisserenc de Bort (1855-1913) from L. stratus "a spreading out" (from p.p. stem of sternere "to spread out") + -sphère (→ sphere), as in atmosphère.

Cine-sepehr, from Ciné, → stratum, + sepehr, → sphere.

A partnership of NASA and the German Aerospace Center, consisting of an extensively modified Boeing 747SP aircraft carrying a reflecting telescope with an effective diameter of 2.5 m. NASA Ames Research Center manages SOFIA's science and mission operations in cooperation with the Universities Space Research Association and the German SOFIA Institute. SOFIA is the largest airborne observatory in the world, with a planned 20-year lifetime.

→ stratospheric; → observatory; → infrared; → astronomy.

1) A long, narrow mark, smear, band of color, or the like.
2) Mineralogy: The color that minerals leave behind when scratched against a black or white porcelain plate. It is used to identify the mineral.

From M.E. streke, from O.E. strica; akin to O.H.G. strich "line."

Xaš "streak, scratch, stria," maybe from xarâš-, xarâšidan "to scratch;" Proto-Ir. *xrāš- "to scratch" (Cheung 2007), or a variant of xatt, → line.

In → fluid mechanics, the curve defined by the positions of all particles which have passed through a given point. In laboratory experiments, streak line may be displayed by the stream of color resulting from injection of a dye into the flow.

→ streak; → line.

1) (n.) A general term for any river, brook, rivulet or course of running water.
A steady flow of a fluid, small solid particles, or radiant energy. → Magellanic stream. Related concepts: → current (jarayân = جریان); → flow (tacân = تچان).
2) (v.) To move or proceed continuously like a flowing stream.

O.E. stream "a course of water;" cf. O.S. strom, O.N. straumr, Dan. strøm, Swed. ström, Norw. straum, Du. stroom, O.H.G. stroum, Ger. Strom "current, river," from PIE base *sreu- "to flow;" cf. Pers. rud, from Mid.Pers. rôd "river;" O.Pers. rautah- "river;" Skt. srotas- "river," sru- "to flow;" Pali sota- "stream, flood;" Gk. rhoos "a stream, a flowing," from rhein "to flow."

1) Râbé, from dialectal Gilaki râbé "flowing of water or liquid," Semnâni rové "a stream of water flowing beyond control," Pers. colloquial râ (in râ gereftan "to overflow, flow beyond control"); probably from PIE base *rei- "to flow;" cf. Skt. ray- "to flow, run," raya- "stream;" L. rivus "stream, brook;" O.C.S. reka "river;" M.Ir. rian "river, way;" Goth. rinnan "run, flow," rinno "brook;" M.L.G. ride "brook;" O.E. riþ "stream."
2) Râbidan infinitive of râbé.

Hydrology: A steady current in a stream or river.
Oceanography: A deep, narrow, well-defined fast-moving ocean current.

→ stream; → current.

A → stream tube with a small cross section so that the variation of velocity over it is negligible.

→ stream; → filament.

A pipe-shaped volume obtained by drawing → streamlines through every point of a closed curve in the fluid. Since the stream tube is bounded on all sides by streamlines and since, by definition, there can be no velocity across a streamline, no fluid may enter or leave a stream tube, except through its ends. See also → stream filament.

→ stream; → tube.

Any long, narrow piece or thing, as a spray of a plant or a strip of cloud; something that streams. → coronal streamer; → helmet streamer

M.E. stremer, from → stream + -er.

Derafšak, from derafš "flag, banner;" Mid.Pers. drafš "banner;" Av. drafša- "banner;" cf. Skt. drapsá- "flag, banner; drop, spark;" also Fr. drapeau; It. drappo "flag;" Lith. drapana "dress."

1) Fluid mechanics: Any process or instance of flowing.
2) Computer science: A condition of a terminal or modem that has locked into a constant carrier signal, thus preventing the normal flow of data.

Verbal noun of → stream.

An imaginary continuous curve drawn in a fluid so that the tangent at every point of it at any instant of time coincides with the direction of the motion of the fluid at that point. The component of velocity at right angles to the streamline is always zero. If a number of streamlines is considered at a particular instant, the pattern they form gives a good indication of the flow then occurring. Same as → flow line. See also → path line, → stream tube.

→ stream; → line.

The ratio of the peak intensity of the central core of the image of a point source to the corresponding intensity contained in an image obtained in the absence of aberration. An optically perfect system has a Strehl ratio of unity. The ratio may be computed by integrating the area under a → modulation transfer function (MTF) curve and dividing it by the integral over the diffraction-limited MTF.

In honor of Karl Strehl (1864-1940), the German physicist and mathematician who introduced the concept; → ratio.

The quality or quantity of force, power, resistance, etc. → line strength.
Mechanics: The ability of a material to resist → stress without yielding or fracture.

M.E., from O.E. strengþu "power, force, vigor, moral resistance," (cf. O.H.G. strengida "strength"), noun of strong.

Zur "strength," variant zâvar; Mid.Pers. zôr "strength, power, vigour," zâvar "strength, force," zôrik "powerful," loaned in Arm. zaur; Av. zāvar- "strength."