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

An axiom in → statics, stating that any → constrained body can be treated as a → free body detached from its → constraints, provided the latter are represented by their → reactions.

→ axiom; → constraint.

A type of → interstellar dust grains with a size ranging from 150 to 1000 Å. Big grains consist of graphite and silicates. They are in → thermal equilibrium with the radiation field and their emission can be described by a modified → blackbody radiation following from → Kirchhoff's law.

→ big; → grain.

The main focus in → Cassegrain telescope.

→ Cassegrain telescope; → focus.

A reflecting telescope whose primary mirror has a hole bored through the center to allow the reflected light from the convex secondary mirror be focused beyond the back end of the tube.

Cassegrain, named after the French priest and school teacher Laurent Cassegrain (1629-1693), who invented this system in 1672; → telescope.

To confine forcibly, as by bonds; to force, compel, or oblige; to repress or restrain. → constrained body, → constrained system.

→ constraint.

A → rigid body whose displacement is prevented because it is under → constraint or a body that can move only in certain directions. Contrasted with → free body.

Constrained, p.p. of → constrain; → body.

Opposite of a → free system. See also → constraint.

Constrained, p.p. of → constrain; → system.

1) General: Limitation or restriction.
2) Mechanics: Any restriction imposed on the position or motion of a material system. Constraints are said to be internal if they do not impede free displacement of the system. All other kinds of constraints are called external. Systems subject only to internal constraints are free material systems.
3) Physics: A fact or condition, usually observational, that allows to reduce the number of free parameters in a theoretical model.

M.E. constreinte, from M.F., from constreindre, from L. constringere "to bind together, tie tightly," from → com- "together" + stringere "to bind, draw tight."

Pâvand "fetter, shackle," from pâ "foot" (Mid.Pers. pâd, pây; Khotanese fad; Av. pad-; cf. Skt. pat-, Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot, E. foot, Ger. Fuss, Fr. pied; PIE *pod-/*ped-) + vand, variant band "tie, band," (Mod.-Mid./Pers. bastan/vastan "to bind, shut," Av./O.Pers. band- "to bind, fetter," banda- "band, tie," Skt. bandh- "to bind, tie, fasten," PIE *bhendh- "to bind," cf. Ger. binden, E. bind).

Material that condenses in the Sun's corona and appears to rain down into the chromosphere, as observed at the solar limb above strong sunspots.

→ coronal; → rain.

A unit used to express the strength of → far ultraviolet (FUV) average → interstellar radiation field. It is equal to ~ 1.7 → Habing field.

Named after B. T. Draine, 1978, ApJS 36, 595.

A small, solid flake of → graphite and/or → silicates coated with water ice, found in the → interstellar medium or the → interplanetary medium. Dust grains are irregularly shaped with sizes from microns to Angstroms (→ very small grain; → big grain; → PAH). It is believed that the dust is mainly formed in the cool outer layers of → red giants and dispersed in the interstellar medium. In dense environments, such as → molecular clouds and around → protostars, dust grains grow due to collisions (→ grain growth). Therefore, dust grains in → protostellar disks should be larger than interstellar grains. Dust grains absorb and scatter optical and ultraviolet light and re-radiate in infrared (→ dust emission). Dust acts as a catalyst in the interstellar medium, because molecules form via reactions on the surface of dust grains.

→ dust; → grain.

An aggregate of small particles loosely stuck together. Same as → porous dust grain.

→ fluffy; → dust; → grain.

1) A small, hard seed of plants, especially the seed of cereals.
2) A tiny portion or particle of something such as sand or salt; → dust grain.

M.E. grain, grein, from O.Fr. grein, from L. granum "seed;" akin to corn.

Dâné "grain, seed;" Mid.Pers. dân, dânag "seed, corn;" Av. dānô- in dānô.karš- "carrying grains; an ant;" cf. Skt. dhânâ- "corn, grain;" Tokharian B tāno "grain;" Lith. duona "corn, bread."

Sticking together of micron- to centimetre-sized grains occurring in the interstellar and protoplanetary environments to form larger grain agglomerates.

→ grain; → coagulation.

Conversion of dust grains into smaller grains due to high environmental temperatures.

→ grain; → evaporation.

The process by which dust grains are assembled or produced.

→ grain; → formation.

The increase of dust grains to micron sizes in the interstellar environments due to various physical processes, for example mutual collisions and accumulation of ice mantles.

→ grain; → growth.

A layer of icy molecules covering interstellar dust grains.

→ grain; mantle, from O.E. mentel "loose, sleeveless cloak," from L. mantellum "cloak," perhaps from a Celtic source.

Rupuš "overgarment, cloak," from ru "surface, face; aspect; appearance" (Mid.Pers. rôy, rôdh "face;" Av. raoδa- "growth," in plural form "appearance," from raod- "to grow, sprout, shoot;" cf. Skt. róha- "rising, height") + puš "covering, mantle," from pušidan "to cover; to put on" (Mid.Pers. pôšidan, pôš- "to cover; to wear;" cf. Mid.Pers. pôst; Mod.Pers. pust "skin, hide;" O.Pers. pavastā- "thin clay envelope used to protect unbaked clay tablets;" Skt. pavásta- "cover," Proto-Indo-Iranian *pauastā- "cloth").

The ejection of atoms from interstellar dust grains due to impact by gas ions, which leads to grain destruction.

→ grain; sputtering, from sputter "to spit with explosive sounds," cognate with Du. sputteren.

Osparâni, verbal noun of osparândan, from os- "out of, outside," → ex- + parândan "to eject," transitive of paridan "to fly" (from Mid./Mod.Pers. par(r) "feather, wing," Av. parəna- "feather, wing;" cp. Skt. parna "feather," E. fern; PIE *porno- "feather").

→ dust grain.

→ interstellar; → dust; → grain.