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

A very bright crescent of light glowing on the lunar horizon at → sunset or just before → sunrise. It has been suggested that → lunar dust is transported electrically high into sky, allowing sunlight to scatter and create glows. On the day side of the → Moon, solar → ultraviolet radiation is strong enough to kick → electrons from → dust grains in the lunar soil. Removal of electrons, which have a negative electric charge, leaves the dust with a positive electric charge. Since like charges repel, the positively charged dust particles get pushed away from each other, and the only direction not blocked by more dust is up. In the 1960s, Surveyor probes filmed a glowing cloud floating just above the lunar surface during sunrise. Later, Apollo 17 astronaut Gene Cernan, while orbiting the Moon, recorded a similar phenomenon at the sharp line where lunar day meets night, called the → terminator.

→ lunar; → horizon; → glow.

The mass of a fluid that passes a specified unit area in a unit amount of time.

→ mass; → flow.

The flowing out of mass through various processes from an object, for example in a star forming region or in a close binary.

→ mass; → outflow.

Meteo.: A flow between the poles, or between the equator and the poles. A positive value indicates flow away from the equator; a negative value, flow toward the equator.

→ meridional; → flow.

An outflow of molecular material, often → bipolar, observed in the regions of → star formation. Molecular outflows are thought to be driven by → bipolar jets from → protostars. They are probably → bow shocks which have had time to cool and be observable in molecular lines. Molecular outflows are poorly → collimated compared to the jets and tend to be slow moving (velocities 10-20 km s^-1). Some bipolar outflows may be driven by → stellar winds.

→ molecular; → outflow.

Same as → airglow.

→ night; → glow.

A hypothetical flow in which all the flow parameters may be expressed as functions of time and one space coordinate only. This single space coordinate is usually the distance measured along the center-line of some conduit in which the fluid is flowing (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

→ one; → dimensional; → flow.

The act of flowing out; a fluid that flows out; any outward movement. Opposite of → inflow.

→ out + → flow.

In computers, the condition arising when the result of an arithmetic operation exceeds the capacity of the number representation.

→ over-; → flow.

Sarriz, from sar, → head, + riz present stem of rixtan "to flow, to pour" (Mid.Pers. rēxtan and rēcitan "to flow;" Av. raēk- "to leave, set free; to yield, transfer," infinitive *ricyā; Mod.Pers; rig in morderig "heritage" (literally, "left by the dead"); cf. Skt. rinakti "he leaves," riti- "stream; motion, course;" L. rivus "stream, brook;" Old Church Slavic rēka "river;" Rus. reka "river;" Goth. rinnan "run, flow," rinno "brook;" O.E. ridh "stream").

A process in a → binary system when a star fills its → Roche lobe, often by becoming a → giant or → supergiant during the later stages of → stellar evolution. When the star expands, any material that passes beyond the Roche lobe will flow onto the binary → companion, often by way of an → accretion disk. This occurs through the → inner Lagrangian point where the gravity of the two stars cancels. The RLOF is responsible for a number of phenomena including → cataclysmic variables, → Type Ia supernovae, and many → X-ray binary systems.

→ Roche lobe; → overflow.

Of little depth; not deep.

M.E. schalowe, akin to O.E. sceald "shallow."

Nažal, from negation prefix na-, → non-, + žal "deep," variant of jal, jol, jul, → deep.

Low angle, → grazing incidence.

→ shallow; → angle.

The illumination of the night sky in urban areas caused by wasted light shining upward scattered off dust, humidity, and air. Skyglow is a type of → light pollution that results from light fixtures emitting a portion of their light directly upward into the sky. Light scattered in the atmosphere creates an orange-yellow glow above a city or town. Skyglow interferes with sensitive astronomical instruments designed to capture light from distant stars, nebulae, and galaxies. Skyglow can often be detected hundreds of kilometers away.

→ sky; → glow.

Nur, → light; foruq, → glow; šahr, → city; âsmân, → sky.

Moving or proceeding with little or less than usual speed or velocity.

O.E. slaw "inactive, sluggish;" cf. O.S. sleu "blunt, dull," M.Du. slee, Du. sleeuw "sour, blunt," O.H.G. sleo "blunt, dull," O.N. sljor, Dan. sløv, Swed. slö "blunt, dull."

Âhesté "slow, quiet, tender, soft," ultimately from Proto-Iranian *ā-hasta-ka-, literally "at rest, motionless, seated." The first and third components are affixes, the main component from *had- "to "sit, be seated;" cf. Av. had- "to sit" (nī...hazdiiāt "would sit down"); Pers. nešastan "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.

A neutron whose kinetic energy does not exceed about 10 electron-volts. Also called → thermal neutron.

→ slow; → neutron.

A type of nova whose light curve exhibits a characteristically slow development, having a rise time of several days, maximum of several weeks, and slower decline.

→ slow; → nova.

A member of a class of → B stars that are situated along the → main sequence with → spectral types ranging from B2 to B9 and masses from 3 to 7 → solar masses. In the → H-R diagram the SPB group lies below → beta Cephei variables, which are more massive. SPBs show light and line-profile variations that are multi-periodic with periods of the order of days. This variability is understood in terms of non-radial → stellar pulsations, and their → oscillation modes are high-order → g modes. Theoretical models attribute the pulsational nature of SPBs to the → kappa mechanism, acting in the metal → opacity bump at 2 x 10⁵ K. Their g-mode pulsations penetrate deep into the stellar interior, making these objects very promising for → asteroseismology. Several oscillation modes are excited simultaneously, resulting in periodicities on time scales of the order of months or even years. The prototype of this group is 53 Per. First introduced as a distinct class by Waelkens (1991, A&A 246, 453).

→ slow; → pulsating; → B star.

A piece of equipment mounted on the front of a vehicle for clearing away snow from roads, railroad tracks, etc.

→ snow + plow, → Plough.

Barfrub, from barf, → snow, + rub, rubidan "to sweep," → scan.

The third phase in the evolution of a → supernova remnant (SNR) occurring after the → Sedov-Taylor phase when the mass of the swept-up material becomes much larger than the amount of the ejected material. The SNR is surrounded by a cool → shell of accumulated material that is being pushed from behind, similar to what occurs for a snowplow. During this phase, → radiative cooling becomes important and the total energy is no longer conserved. Also called the → radiative phase.

→ snowplow; → phase.

A flow in which the characterizing conditions, such as → streamlines or velocity at any given point, do not change with time.

→ steady; → flow.

Tacân, → flow; pâyâ "steady, constant," from pâyidan "to stand firm, to be constant, steady," from Mid.Pers. pattây-, pattutan "to last, endure, stay."