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

1) Flow of matter during an accretion process.
2) In a → binary system, flow of matter from the losing-mass → companion toward the compact one. The flow can be from a → stellar wind or through the → inner Lagrangian point.
3) → cold accretion flow, → hot accretion flow.

→ accretion; → flow.

1) A broad glowing arc of radiance, sometimes seen high in the western sky at → twilight, caused by the → scattering effect of → fine dust particles suspended in the → upper atmosphere.
2) Lingering → radiation that remains after a violent → event such as a → gamma-ray burst. The afterglow of any gamma-ray burst is caused by an event different from the original explosion, likely by → shock waves colliding with the ambient medium. Afterglows occur in a large range of → electromagnetic  → wavelengths.

→ after; → glow.

The faint ever-present glow in the → night time → sky caused by the → collision of → atoms and → molecules in Earth's → upper atmosphere with high energy → particles and → radiation, mainly from the → Sun. The airglow, also called nightglow, varies with time of night, → latitude, and → season.

→ air; → glow; → night.

In solid-state physics, the range of energies which electrons can attain in a material.

P.p. of v. allow, from O.Fr. alouer "approve," from L. allaudare , compound of → ad- "to" + laudare "to praise."

Bând, → band; parzâmidé, p.p. of parzâmidan "to send through, permit, allow," from parzâm "permission," from par- "through" + zâm stem of zâmidan, Mid.Pers. zâmenidan "to send, lead;" → permit

A → negative lens placed in a telescope between the → objective and the → ocular. Its diverging action reduces the convergence of the light cone, forming a larger image at a slightly greater distance.

Peter Barlow (1776-1862), English physicist; → lens.

Same as → bipolar outflow.

→ bipolar; → flow.

A flow of gaseous material in two opposite directions emanating from protostellar regions or from → evolved stars during the early post-→ AGB evolution. In protostellar regions → molecular outflows are pushed by → bipolar jets.

→ bipolar; → outflow.

Ostacân, → outflow; doqotbi→ bipolar.

1) To move along, carried by or as by the wind.
2) To produce or emit a current of air, as with the mouth or a bellows.
3) Of a horn, trumpet, etc.) to give out sound.
4) To make a blowing sound; whistle (Dictionary.com).

M.E., from O.E. blawan "blow, breathe, make an air current; kindle; inflate; sound a wind instrument;" cf. O.H.G. blaen, Ger. blähen; from PIE *bhle- "to swell, blow up."

Damidan, from Mid.Pers. damidan "to blow, breathe;" dam "breath, breath of an owen; bellows; smoke; air," also "moment, time;" Av. dāδmainya- "blowing up;" cf. Skt. dahm- "to blow," dhámati "blows;" Gk. themeros "austere, dark-looking;" Lith. dumti "to blow;" PIE dhem-/dhemə- "to smoke, to blow."

The flow of → ionized gas escaping from a → molecular cloud due to the → champagne effect.

→ flow.

A stream of matter into the interstellar medium from a central star.

→ circumstellar; → outflow.

1) A type of → accretion flow by a → compact object such as a → black hole that consists of cool → optically thick gas and has a relatively high mass → accretion rate, in contrast to → hot accretion flows.
2) Gas accreting from the → intergalactic medium (IGM) onto → galactic haloes with sufficiently low velocities so that it will not be shocked to the → virial temperature of the halo, but will instead flow at a relatively low temperature (T ~ 10⁴ K). Galaxies grow by accreting gas from → cosmic filaments. Feedback from star formation and → active galactic nuclei returns a significant fraction of the → interstellar medium (ISM) to the halo and may even blow it out of the halo into the IGM. This "cold accretion" will happen if the cooling time of → virialized gas is too short to maintain a hot, → hydrostatic halo. The existence of such a cold accretion mode has been confirmed by simulations, which have furthermore demonstrated that cold mode accretion can also be important for halos sufficiently massive to contain hot, hydrostatic gas. Because gas accretes preferentially along the filaments of the cosmic web, the streams of infalling gas have relatively high gas densities and correspondingly low cooling times. This allows the cold streams to penetrate the hot, hydrostatic halos surrounding massive galaxies, particularly at → high redshifts (F. van de Voort et al., 2012, MNRAS 421, 2809).

→ cold; → accretion; → flow.

A flow in which changes of the density, induced by velocities and their fluctuations, are not negligible.

→ compressible; → flow.

A phenomenon observed in a → cluster of galaxies, whereby the cluster core loses energy via X-ray radiation because of the collisions between the gas particles. The radiation rate is proportional to the square of the density, and the → cooling time, which remains in the outer parts too large, becomes smaller than the → Hubble time in the core. As a result, the central regions of clusters of galaxies cool down; and since in the center of a cluster gas pressure and gravitational attraction are in equilibrium, the gas density has to rise to maintain the pressure necessary for supporting the outer layers of gas. To cause its density to rise, the cooled gas has to flow inward. As the densest gas, which cools quickest, is already concentrated in the center of the cluster, the inward flow will start at the center, soon followed by the outer layers. This flow of gas is called the cooling flow. Cooling flows are moderated through feedback due to the → supermassive black hole in the nucleus of the central galaxy. The gas inflow to the center fuels the → active galactic nucleus (AGN). The latter then heats again the gas through its → radio jets.

→ cooling; → flow.

In fluid dynamics, the motion of an → incompressible → laminar flow passing between two parallel plates, when the upper plate is moving with some velocity while the lower one is stationary. The flow is driven owing to the fluid → viscosity and the applied pressure gradient parallel to the plates. See also → Taylor-Couette flow.

Named after Maurice Marie Alfred Couette (1858-1943), a French physicist who dealt mainly with fluid mechanics; → flow

In fluid mechanics, the motion of a fluid between two concentric cylinders when one or both of the cylinders rotate.

→ Couette flow; Geoffrey Ingram Taylor (1886-1975), British physicist; → flow.

The movement of a fluid in the opposite direction to a fluid flowing in the same cross section of a turbulent medium.

→ counter-; → flow.

Same as → gegenschein.

1a) Moving along in a → stream; going as in a stream.
1b) A → dynamical system that evolves continuously with time.
1c) The transference of energy.
2) The corresponding verb.

O.E. flowan, from P.Gmc. *flo- (cf. Du. vloeien "to flow," O.H.G. flouwen "to rinse, wash"), probably from PIE *pleu- "to flow, float" (cf. Skt. plavate "navigates, swims," plavayati "overflows;" Gk. plyno "I wash," pleo "swim, go by sea;" L. pluere "to rain;" Arm. helum "I pour;" Lith. pilu "to pour out").

1) Tacân, from tac- variant tâz- present stem of tacidan, tâxtan, tâzidan "to run; to hasten; to assault," + noun and adj. suffix -ân. Related to the first component are Mod.Pers. tajan name of a river (initially "flowing, streaming, stream"), tâzi "swift (greyhound)," tak "running, rush," from Mid.Pers. tâz-, tâxtan "to flow, to cause to walk," tc- "to flow, to walk," tag "running, attack," tâzig "swift, fast;" Khotanese ttajs- "to flow, to walk;" Av. tac- "to run, to flow," taciāp- "flowing water," tacinti (3pl.pers.act.) "to flow," tacar- "course," tacan "current, streaming;" cf. Skt. tak- "to rush, to hurry," takti "runs;" O.Ir. tech- "to flow;" Lith. teketi "to walk, to flow;" O.C.S. tešti "to walk, to hurry;" Tokharian B cake "river;" PIE base *tek^w- "to run; to flow."
2) Verbal form.

Same as → streamline.

→ flow; → line.

The amount of a substance, specifically a → fluid, moving across a specified unit → area in a given amount of → time.

→ flow; → rate.