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

A system comprised of a group of stars bound by → gravitational attraction. Same as → star system.

→ stellar; → system.

The steady flow of gas away from a star resulting in → mass loss. They range from gentle solar wind (2 x 10^-14 solar masses per year) to violent winds some 10 billions times stronger (10^-4 solar masses per year) for hot, massive stars.

→ stellar; → wind.

Same as → stellar black hole.

→ stellar; → mass; → black; → hole.

Math.: A function f of a real variable defined on an interval [a,b] so that [a,b] can be divided into a finite number of sub-intervals on each of which f is a constant. The graph of a step function is a series of line segments resembling a set of steps.

Step, from M.E. steppen, O.E. steppan; cf. Du. stap, O.H.G. stapfo, Ger. stapfe "footprint;" → function.

Karyâ, → function; pellé "stair, step;" Mid.Pers. pylg "step," pillagân "steps, staircase;" from *palak, from *padak, from pad-, → foot, + relation suffix -ak.

A group of five closely grouped galaxies (NGC 7317, 7318A, 7318B, 7319 and 7320) in the constellation → Pegasus. Four of the galaxies show essentially the same → redshift, suggesting that they are at the same distance from us. The fifth galaxy (NGC 7320) has a smaller redshift than the others, indicating it is much closer. This one is probably a foreground galaxy which happens to lie along the line of sight. The four distant galaxies seem to be colliding, showing serious distortions due to gravitational → tidal forces. The NASA → Spitzer Space Telescope has revealed the presence of a huge intergalactic → shock wave. Collisions play an important role in the life cycles of galaxies. → merging galaxies.

Named after the French astronomer Edouard Stéphan (1837-1923), who discovered the group in 1877 at Marseilles Observatory, using the → Foucault's reflector; → quintet.

The solid angle subtended at the center of a sphere by an area on its surface numerically equal to the square of the radius. → square degree.

From ste(reo)-, → stereo- + → radian.

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.

Incapable of producing offspring; not producing offspring (Dictionary.com).

M.Fr. stérile "not producing fruit," from L. sterilis "barren, unproductive, unfruitful," from PIE *ster- "stiff, rigid, firm, strong."

Satarvan, literally "mule-like, resembling a mule," from setar, variant of astar, → mule, + -van similarity and attribution suffix.

A hypothetical type of → neutrino which does not participate in the → weak interaction. It would arise only from ordinary neutrinos oscillating into a sterile form (singlet, right handed → helicity). The sterile neutrino is a candidate for the → dark matter. Sterile neutrinos might have been produced in primordial plasma in the → early Universe. The idea of sterile neutrino was first proposed by Bruno Pontecorvo (1967) in a paper which also discussed neutrino oscillations.

→ sterile; → neutrino.

An experiment devised for measuring the → magnetic moment of → silver atoms. A → beam of silver atoms is directed between the → poles of a non-homogeneous → magnetic field. Contrarily to the prediction of the classical theory, the atoms divide into two distinct parts. One half of atoms are deflected up, the other half deflected down. The amount of deflection up or down is exactly of the same magnitude. Whether an individual atom is deflected up or down appears to be random. From a measurement of the → deflection, one can find the strength of the magnetic moment. This experience provides proof that there exist only two permitted orientations, called the → quantization of → spin.

In honor of Otto Stern (1888-1969), German physicist, Nobel laureate in Physics 1943, and Walter Gerlach (1889-1979), German physicist, who carried out the experiment in 1922. They used a beam of silver atoms from a hot oven because they could be readily detected on a photograph emulsion. Moreover, the silver atoms allowed studying the magnetic properties of a single electron because the atoms have a single outer electron; → experiment.

Optics: A unit of luminance equal to one candle per square cm.

From Gk. stilbe "lamp."

To cause physical activity in something; e.g. → stimulated emission.

Verb from → stimulus.

The process by which an electron, which is already in an excited state (an upper energy level, in contrast to its lowest possible level or "ground state"), can "stimulate" a transition to a lower level, producing a second photon of the same energy. The quantum energy of the incoming photon should be equal to the energy difference between its present level and the lower level. This process forms the basis of both the → laser and → maser. Same as → induced emission.

Stimulated, p.p. of → stimulate; → emission.

A process in which a star is not formed spontaneously but is provoked by the action of external forces, such as pressure and shock on a molecular cloud by close-by → massive stars, → supernova explosions, etc. See also → sequential star formation.

Stimulated, p.p. of → stimulate; → star formation.

Something that incites or rouses to action; an incentive.
Physiology: Something that causes a physical response in an organism,

From L. stimulus "goad, spur;" cognate with Pers. tiz→ sharp.

Gavâz "goad, a stick with a pointed end, for driving cattle," Mid.Pers. *gawâz, lowned in Arm. gawazan "goad;" Av. gauuāza- "whip, stick for driving cattle," from gao- "cattle, cow" (→ Bootes) + āza-, from az- "to drive," azaiti "drives;" cf. Skt. aj- "to drive," ájati "drives;" Gk. agein "to lead, guide, drive;" L. agere "to do, set in motion," → act.