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

The observation and measurement of the flatness of a mirror surface. The process generally is done before coating so as not to damage the delicate coated surface. For coated and curved surfaces, non-contact methods are often employed, generally using interference techniques.

→ mirror; → test.

The support structure for a telescope that bears the weight of the telescope and allows it to be pointed at a target.

From verb mount, from O.Fr. monter "to go up, climb, mount," from V.L. *montare, from L. mons (genitive montis) → mountain

Barnešând, noun of Barnešândan "to set, to fix, make sit," from bar- "on, upon, up" (Mid.Pers. abar; O.Pers. upariy "above; over, upon, according to;" Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + nešândan "to place one thing upon another, to fix, insert," from nešastan "to sit;" Mid.Pers. nišastan "to sit;" O.Pers. nišādayam [1 sg.impf.caus.act.] "to sit down, to establish," hadiš- "abode;" Av. nišasiiā [1 sg.subj.acr.] "I shall sit down," from nihad- "to sit down," from ni- "down, below, into," → ni-, + had- "to sit;" PIE base *sed- "to sit;" cf. Skt. sad- "to sit," sidati "sits;" Gk. hezomai "to sit," hedra "seat, chair;" L. sedere "to sit;" O.Ir. suide "seat, sitting;" Welsh sedd "seat;" Lith. sedmi "to sit;" Rus. sad "garden;" Goth. sitan, Ger. sitzen; E. sit.

The part of a nebular object's → spectrum that is created by → free-free emission.

→ nebular; → continuum.

Describing a → proposition that is either → true in every possible circumstance or → false in every possible circumstance. A proposition that is not → contingent.

→ non-; → contingent.

A star that is always seen above the horizon from a given position. These stars are located between the celestial pole and a diurnal circle with an angular distance smaller than the altitude of the pole. Same as → circumpolar star.

Nonsetting, from → non- + setting adj. of → set; → star.

Setâré, → star; hamiše peydâ literally "always visible," coined by Biruni (A.D. 973-1050) in his at-Tafhim, from hamišé "always," → perpetual, + peydâ, → visible.

A diffraction grating placed over the aperture of a telescope in order to produce spectra of all the objects in the field of view.

→ objective; → grating.

The program that, after being initially loaded into the → computer by a boot program, → manages all the other → programs in a computer.

→ operating; → system.

A cosmological model in which the Universe is closed and undergoes a series of oscillations, each beginning with a big bang and ending with a big crunch.

Oscillating, verbal adj. of → oscillate; → universe.

Relating to → osculate.

Participial adjective of → osculate.

The circle that touches a curve (on the concave side) and whose radius is the radius of curvature.

→ osculating; → circle.

The orbital elements of an osculating orbit.

→ osculating; → element.

The Keplerian orbit that a satellite would follow after a specific time t if all forces other than central inverse-square forces ceased to act from time t on. An osculating orbit is tangent to the real, perturbed, orbit and has the same velocity at the point of tangency.

→ osculating; → orbit.

For a curve C at a point p, the limiting plane obtained from taking planes through the tangent to C at p and containing some variable point p' and then letting p' approach p along C.

→ osculating; → plane.

For a curve C at a point p, the limiting sphere obtained by taking the sphere that passes through p and three other points on C and then letting these three points approach p independently along C.

→ osculating; → sphere.

A situation in stellar interiors when the momentum of a particle carries it past its equilibrium point.

→ over-; shooting, from shoot, from O.E. sceotan "to shoot" (cf. O.N. skjota, Du. schieten, Ger. schießen), from PIE base *skeud- "to shoot, to chase, to throw, to project."

Farâzad, from farâ- "over, over against; foremost; before; onward" (Mid.Pers. fra-; O.Pers. fra- "forward, forth;" Av. frā "forth," pouruua- "first"; cf. Skt. pūrva- "first," pra- "before, formerly;" Gk. pro; L. pro; O.E. fyrst "foremost," superlative of fore, E. fore) + zad past stem of zadan "to strike, beat, dash against; to shoot" ( Mid.Pers. zatan, žatan; O.Pers.; Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike," phonos "murder;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *g^when- "to strike, kill").

The supersymmetric partner of the → photon.

From phot, from → photon + -ino supersymmetric particle suffix.

A heating process occurring in → diffuse molecular clouds which is believed to be the main heating mechanism in cool → H I regions. Far-ultraviolet (FUV) photons, in the energy range 6 eV <hν < 13.6 eV, expel electrons from → interstellar dust grains and the excess → kinetic energy of the electrons is converted into gas → thermal energy through → collisions. The high energy limit corresponds to the cut-off in the → far-ultraviolet (FUV) radiation field caused by the hydrogen absorption (hν = 13.6 eV), while the low energy limit corresponds to the energy needed to free electrons from the grains (hν ~ 6 eV). In the cold neutral medium (T_kin≥ 200 K) photoelectric heating accounts for most of the heating, the → X-ray and → cosmic ray heating rates (→ cosmic-ray ionization) being more than an order of magnitude smaller. In a relatively dense neutral medium (n_H≥ 100 cm^-3), where a significant fraction of carbon is in the neutral form, carbon ionization becomes an important heating source, but it is still not comparable to the photoelectric effect. The heating rate cannot be directly measured, but it can be estimated through observations of the [C II] line emission, since this is believed to be the main → coolant in regions where the photoelectric heating is dominant (See, e.g., Juvela et al., 2003, arXiv:astro-ph/0302365).

→ photoelectric; → heating.

A function f(x) in an interval if :1) the interval can be divided into a finite number of pieces in each of which f(x) is continuous, and 2) the limits of f(x) as x approaches the boundary point of each piece are finite. In other words, a piecewise continuous function is one that is made up of a finite number of continuous pieces.

→ piecewise; → continuous; → function.

A silvery metallic → chemical element which is tenacious, malleable, and ductile; symbol Pt. → Atomic number 78; → atomic weight 195.08; → melting point 1,772°C; → boiling point 3,827±100°C; → specific gravity 21.45 at 20°C; → valence +2 or +4. It has several short-lived → radioactive isotopes, with the exception of ¹⁹⁰Pt whose → half-life is 6.0 x 10¹¹ years.

From Sp. platina diminutive of plata "silver," from O.Fr. → plate "sheet of metal." The first known reference to platinum can be found in the writing of Italian physician, scholar, and poet Julius Caesar Scaliger (1484-1558). He reported seeing the metal during a visit to Central America in 1557. Aborigines knew of no use for the metal and regarded it as a nuisance in their search for gold and silver. By the end of the 17th century, the Spanish conquistadors started developing the river soil looking for gold and found some gray looking beads together with the gold. They called those little silver beads platina "small silver." They became known as platina del Pinto "granules of silvery material from the Pinto River," a tributary of the San Juan River in the Chocó region of Colombia. The first complete description of platinum was given in 1735 by the the Spanish explorer and naval officer Antonio de Ulloa (1716-1795).

Pelâtin, loanword from Fr.

One of the six metals → platinum (Pt), → iridium (Ir), → osmium (Os), → palladium (Pd), → rhenium (Rh), and → ruthenium (Ru) that are grouped together in the → periodic table. They are relatively hard and resistant to corrosion and are used in jewellery and in some industrial applications. All are resistant to chemical attack.

→ platinum; → group; → element.