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

The powdery residue that remains after something is burnt. → ashen light.

M.E. a(i)sshe; O.E. asce, æsce; cf. Frisian esk, Dutch asch, O.N., O.H.G. aska, Ger. Asche; akin to Gk. azein "to dry up, parch," L. arere "be dry," → arid, Skt. asa- "ashes," PIE root *as- "to burn, glow."

Xâkestar, ultimately from Proto-Iranian *aika-âtar- literally "fire dust," from *aika- (Pers. xâk "dust, earth," → soil) + *ātar- (Pers. âzar, âtaš, → fire); cf. Malâyeri xâkesar, Qasrâni xâksar.

The faint glow occasionally observed on the unlit area of Venus in its crescent phase. Its cause is not known with certainty, but it might result from bombardment of atmospheric atoms and molecules by energetic particles and radiation, as with terrestrial airglow.

→ ash; → light.

A → bipolar nebula and → OH/IR source with technical designation OH 231.8+4.2. It is a → proto-planetary nebula (PPN) 1.4 → light-years long and located some 5,000 light-years from Earth in the constellation → Puppis. The obscured → central star, named QX Pup, is classified as M9-10 III and has a → Mira-like variability consistent with an evolved → asymptotic giant branch (AGB) star. The late evolution of this object may have been complex since it has a binary → companion star (of type A0 V) that has been indirectly identified from analysis of the spectrum of the hidden central source reflected by the nebular dust. The system has a total luminosity of ~ 10⁴ Lsun and its systemic velocity relative to the → Local Standard of Rest is V_LSR ~ 34 km s^-1. OH 231.8+4.2 is very likely a member of the → open cluster M46 with a progenitor mass of ~ 3 Msun. The nebula is also known as the Rotten Egg Nebula because it contains a lot of sulphur, an element that, when combined with other elements, smells like a rotten egg (see, e.g., Prieto et al., 2015, A&A, 575, A84).

The name "Calabash Nebula" was first proposed by Icke & Preston, 1989, A&A, 211, 409. It refers to the apparent form of the object which resembles a calabash "a tree that has large, rounded gourdlike fruit; the fruit of any of these plants," from Sp. calabaza, possibly from Ar. qar'ah yâbisah "dry gourd," from Pers. kharabuz, used of various large melons; → nebula.

A galaxy at a → redshift of z = 2.3259 lying behind a massive → cluster of galaxies and magnified by the → lensing effect of the cluster. It was first discovered in → submillimeter waves. The lensing cluster lies at a redshift z > 1.5 causing an → amplification factor for the background galaxy of 32 (A. M. Swinbank et al. 2010, Nature 464, 733).

→ cosmic; eyelash, from → eye + lash, from M.E. lashe (n.) lashen (v.) "to blow, stroke." Such called because of its narrow and elongated shape.

Možé "eyelash," from Mid.Pers. mec "eyelash," mecitan "to blink;" cf. Skt. mes "to open the eyes;" O.C.S. po-mežiti "to close the eyes;" keyhâni, → cosmic.

A Sudden, brief burst of light. In particular, → green flash.

From M.E. flasshen "to sprinkle, splash," from flasken, probably imitative.

Deraxš, present stem of deraxšidan "to shine, radiate," from raxš "lightening, reflection of light," raxšidan "to shine, flash," O.Pers. raucah-, Av. raocah- "light" (cf. Skt. roka- "brightness, light," Gk. leukos "white, clear," L. lux "light" (also lumen, luna), E. light, Ger. Licht, Fr. lumière; PIE base *leuk- "light, brightness"); cognate with Mod.Pers. words ruz "day," rowšan "bright, clear," foruq "light," and afruxtan "to light, kindle."

The spectrum of the solar → chromosphere obtained during a → solar eclipse in the instant before or after → totality. In the flash spectrum the usual solar → absorption lines are replaced with bright → emission lines. This is because in that very short interval only the → photosphere is eclipsed by the Moon, and not the chromosphere. The American astronomer Charles A. Young was the first to observe it during the the solar eclipse of 1870 (December 22) in Spain.

The flash designation comes from the fact that the change from dark-line to bright-line spectrum is very rapid; → flash; → spectrum.

A brilliant green color that occasionally appears on the upper limb of the Sun as it rises or sets.

→ green; → flash.

The region to the right the → Hayashi track, representing objects that cannot be in → hydrostatic equilibrium. Energy transport in these objects would take place with a → superadiabatic temperature gradient.

→ Hayashi track; → forbidden; → zone.

A period in the → pre-main sequence evolution of a low mass star during which the star has negligible nuclear energy production and low internal temperature. Hence energy transport inside the star takes place dominantly through → convection. The star contracts homologously and evolves in the → H-R diagram along the → hayashi track with decreasing → luminosity and nearly constant → effective temperature. The time taken by a star of mass M_* to contract to radius R_* along a Hayashi track is of the order of the → Kelvin-Helmholtz time: t_KH = 10⁷(M_*/M_sun)²/(R_*/R_sun)³ yr.

→ Hayashi track; → phase.

The minimum → effective temperature required for a → pre-main sequence star of given mass and radius to be in → hydrostatic equilibrium. This temperature delimits the boundary of the → Hayashi forbidden zone.

→ Hayashi track; → temperature.

The path on the → Hertzsprung-Russell diagram that is followed by a fully → convective  → pre-main sequence star to reach the → zero-age main sequence. Hayashi tracks for → low-mass stars are near vertical. At higher masses, stars become increasingly radiative as they contract and the Hayashi tracks are almost horizontal.

Named after the Japanese astrophysicist Chushiro Hayashi (1920-2010), who published his paper in 1961 (PASJ 13, 450); → track.

The sudden onset of → helium burning in the core of an → intermediate-mass star that has exhausted its hydrogen and has become a → red giant. With a → degenerate core, the temperature increases but the pressure does not. Therefore, the core cannot expand and cool, so the temperature continues to rise. When it approaches 100,000,000 K, helium will begin to fuse into carbon in the → triple alpha process. The helium flash ends the giant star's ascent of the → red giant branch. However, the violent ignition of helium in the core does not increase the star's luminosity. On the contrary, the energy released in the helium flash expands and cools the core and ultimately results in a reduction in the energy output. On the → H-R diagram the star moves down from red giant branch to the → horizontal branch, a stable state with steady helium burning in the core.

→ helium; → flash.

A violent outburst of energy that occurs periodically in an → asymptotic giant branch star. It occurs when helium is being burnt in a thin shell surrounding the inner dense core of carbon and oxygen. → Helium shell burning is unstable, producing energy mainly in short intense flashes. The shell flash causes considerable expansion of the star followed by collapse, thus setting up deep convection. As a consequence, the → convective zone in the outer part of the star goes deeper and may → dredge-up carbon to the surface. See also → late thermal pulse; → very late thermal pulse; → AGB final thermal pulse.

→ helium; → shell; → flash.

A way of measuring a civilization's technological advancement based upon how much usable energy it has at its disposal. The scale was originally designed in 1964 by the Russian astrophysicist Nikolai Kardashev (who was looking for signs of extraterrestrial life within cosmic signals). It has three base classes, each with an energy disposal level: Type I, Type II, and Type III. Type I designates a civilization that is capable of controlling the total energy of its home planet (10¹⁶ watts). Type II is an interstellar civilization, capable of harnessing the total energy output of a star (10²⁶ W). And Type III represents a galactic civilization, capable of inhabiting and harnessing the energy of an entire galaxy (10³⁶ W). The scale has since been expanded by another four. Type 0 is civilization that harnesses the energy of its home planet, but not to its full potential. The Earth civilization is currently at about 0.73 on the Kardashev scale.

The scale was originally designed in 1964 by the Russian astrophysicist Nikolai Kardashev (1932-); → scale.

A → helium flash event that occurs during the → post-AGB phase. Some of the central stars of planetary nebulae (→ CSPN) experience a final → thermal pulse after having achieved a → white dwarf configuration and begun their descent along a → white dwarf cooling track of nearly constant radius. During such a pulse, most of the hydrogen remaining in the star at pulse onset is incorporated into the helium-burning convective shell and completely burned. Following the pulse, the star swells briefly to → red giant dimensions (Iben et al. 1983; ApJ 264, 605).

→ late; → helium; → flash.

Carefully chosen uniform exposure of a detector. For CCD this can be used to overcome the deferred charge phenomenon; in photography this helps bring dim images to a comfortably high density.

→ pre- + → flash.

The hard shell of a marine mollusk.

→ sea; → shell.

Sadaf, loan from Ar. Kelâcak from Tabari, variant kelâcin, cf. Gilaki guš kuli. The component kel-, kul might be related to PIE *qarq- "to be hard," → crab.

An oblique line (/) used between alternatives (e.g. and/or), in fractions (e.g. 4/5), or in percent ratios (e.g. kilometer/hour).

From M.E. slaschen, perhaps from M.Fr. esclachier "to break," variant of esclater "to break, splinter."

Eslaš, loan from E.

A theoretical interpretation for the → X-ray bursts observed toward → low-mass X-ray binary (LMXB) stars. According to models, X-ray bursts are produced on the surface of → neutron stars as a result of violent thermonuclear processes in a → hydrogen or → helium rich → layer. It is the → nuclear energy released in the → fusion of hydrogen and helium to heavier elements (e.g., Ni, Zn, and Se) in the → accreted matter which heats the upper layers of the neutron star so that X-rays are emitted from the surface (see, e.g., Taam, R.E., 1984, AIP Conf. Proc. 115, 263).

→ thermonuclear; → flash.

A → Cepheid star of → spectral type A-F with regular pulsation period of 1-3 hours and with small variations in amplitude. This group is also known as δ Scuti stars.

→ ultra-; → short; → period; → Cepheid.