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

An aberration in an optical instrument, common in Schmidt telescopes, in which the focus changes from the center to the edge of the field of view. Owing to this aberration, a straight object looks curved in the image.

→ field; → curvature.

In a physical theory, an equation that describe how a fundamental force interacts with matter. Einstein's equations of → general relativity are called field equations since they describe the → gravitational field. Similarly, → Maxwell's equations describe the electromagnetic field.

→ field; → equation.

A galaxy that lies in the direction of a → cluster of galaxies, but is not a member of the cluster. Field galaxies are rare, less than about 5% of all galaxies.

→ field; → galaxy.

A → horizontal branch star with high velocity.

→ field; → horizontal; → branch; → star.

A lens placed at or near the focal plane of a telescope to create an image of the primary mirror inside the instrument.

→ field; → lens.

An → O-type star which is apparently not associated with a → star cluster. A significant fraction of → massive stars in the → Milky Way and other galaxies are located far from star clusters and → star-forming regions. It is known that some of these stars are → runaways, i.e. possess high → space velocities (determined through the → proper motion and/or → radial velocity measurements), and therefore most likely were formed in embedded clusters and then ejected into the field because of dynamical interactions or → binary-→ supernova explosions. However, there exists a group of field O stars whose runaway status is difficult to prove via direct proper motion measurements or whose low space velocities and/or young ages appear to be incompatible with their large separation from known star clusters. The existence of this group led some authors to believe that these stars can form → in situ. The question of whether or not O stars can form in isolation (→ isolated massive star formation) is of crucial importance for → star formation models (Gvaramadze et al., 2012, MNRAS, 424, 3037).

→ field; → O star.

An astronomical object that is seen in the direction of a group but not physically belonging to the group. → field galaxy.

→ field; → object.

The region of → space surrounding a body, such as a mass of → matter, a → charged particle, or a → magnet, within which it can exert a → force on another similar body not in contact with it.

→ field; → force.

The entire angular expanse of the sky viewed by an optical instrument.

→ field; → view.

The effect of the Earth's rotation on the position of the image formed on the → focal plane of a telescope during long exposures. In the case of → equatorial mounting, the image remains fixed, whereas it turns continuously with an → altazimuth mounting. In the latter case the image motion must be compensated by an appropriate mechanism, → field rotator.

→ field; → rotation.

A device used on a telescope to correct for the → field rotation while tracking an object.

→ field; → rotator.

A star that does not belong to a stellar cluster, but happens to be adjacent to it.

→ field; → star.

A diaphragm located at an image plane of an optical system that determines the size and shape of the image. → aperture stop.

→ field; → stop.

1) A theory which uses the concept of → field to describe physical phenomena. It consists of two types: → classical field theory and → quantum field theory.
2) Math.: A branch of mathematics which studies the → fields.

→ field; → theory.

The precise curve required on the surface of an optical element, especially the mirror of a reflecting telescope.

From O.Fr. figure, from L. figura "a shape, form."

Šekl from Ar. šakl "figure."

The final stage of mirror making, a process of altering the mirror's shape into the one required for proper function. → grinding; → polishing.

Figuring, noun of → figure.

Šekldahi, "giving form," from šekl, → figure + dahi, a verbal noun of dâdan "to give," from Mid.Pers. dâdan "to give," O.Pers./Av. dā- "to give, grant, yield," dadāiti "he gives;" cf. Skt. dadáti "he gives," Gk. didomi "I give," tithenai "to put, set, place;" L. dare "to give, offer;" facere "to do, to make;" Rus. delat "to do;" O.H.G. tuon, Ger. tun, O.E. don "to do." PIE base *dhe- "to put, to do."

1) A long tongue of a relatively cold matter (10,000 K), suspended in the → solar corona (2 million K). Filaments seem dark in the Hα light when they are seen projected on the solar disk; at the limb they look as what they actually are: → prominences.
2) Electricity, Electronics: In electric light bulbs and thermionic valves, a wire of metal of high melting point, which is heated by the passage of an electric current.
3) Cosmology: → cosmic filament.

From Mod.L. filamentum, from L.L. filare "to spin, draw out in a long line," from L. filum "thread," from PIE base *g^whi- "thread, tendon;" cf. Gk. bios "bow;" Skt. jiyā- "bow-string;" Av. jiiā- "bow-string;" Mod.Pers. zeh "string, bow-string" (dialectal Qomi zij "mason's cord"); Arm. jil "string, line;" Lith. gijà "thread;" Russ. žica "thread."

Rešté "thread, line, file," from reštan, ristan "to spin;" Mid.Pers. 'rws- "to turn to," abrešom "silk;" Sogdian rwyšt "spun;" Av. uruuaēs- "to twist, turn;" Proto-Iranian *uris- "to turn, spin."

A nebula, generally ionized, consisting of filament-like structures of gas, such as the Veil Nebula (NGC 6960) or the supernova remnant IC 443.

Filamentary adj. of → filament; → nebula.

An instrument used with a telescope for accurately measuring small angular separations between two celestial bodies (as between binary stars). The instrument consists of two parallel fine wires with one wire being fixed and the other movable by means of a finely threaded screw.

Filar, from L. fil(um) "a thread" (see the paragraph below) + -ar variant of the adjective-forming suffix → -al; → micrometer.

Kehsanj, → micrometer; zehi adj. of zeh "string, bow-string;" Mid.Pers. zih "bow-string," zig "string; astronomical table" (loaned into Ar. as zij); Av. jiiā- "bow-string;" cf. Skt. jiyā- "bow-string;" Gk. bios "bow;" L. filum "thread;" Arm. jil "string, line;" Lith. gijà "thread;" Russ. žica "thread;" PIE base *g^whi- "thread, tendon."

In computer science, a collection of related data or program records stored on a support.

From M.E. filen, from M.F. filer "to string documents on a thread," O.F. filer "to wind or spin thread," from L.L. filare "to spin, draw out in a long line," from L. filum "thread," from PIE base *g^whi- "thread, tendon;" cf. Gk. bios "bow;" Skt. jiyā- "bow-string;" Av. jiiā- "bow-string;" Mod.Pers. zeh "bow-string;" Arm. jil "string, line," Lith. gijà "thread;" Russ. žica "thread."

Parvandé "file," initially "a bundle, roll, truss (of clothes)," from Mid.Pers. parwastan, parwand- "to surround, enclose, contain, comprise," from par-, variants far-, par-, pirâ- "around, about" (Mid.Pers. pêrâ; O.Pers. pariy "around, about," Av. pairi "around, over;" Skt. pari; Indo-Iranian *pari- "around;" PIE base *per- "through, across, beyond;" cf. Gk. peri "around, about, beyond;" L. per "through") + vand-/band- stem of vastan/bastan "to bind, shut;" O.Pers./Av. band- "to bind, fetter," banda- "band, tie" (cf. Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind;" Ger. binden; E. bind).