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

An act or instance of dominating.

Verbal noun of → dominate.

In a semiconductor, an impurity which may induce electric conduction by providing free electrons. → acceptor; → impurity.

M.E. donour, from O.Fr. doneur, from L. donator, from donare "to give as a gift," donum "gift," dare "to give," cognate with Pers. dâdan "to give," from PIE base *do- "to give."

Dahandé "giver," from dâdan "to give," Mid.Pers. dâdan "to give," O.Pers./Av. dā- "to give, grant, yield," Av. dadāiti "he gives," Skt. dadâti "he gives," Gk. didomi "I give," PIE base *do- "to give." For L. cognates see above.

In a → binary system, a star whose gas is → accreted by a compact companion. The donor may be a → giant or a → supergiant with an enormously distended atmosphere and a significant → stellar wind, or a star filling its → Roche lobe in a → close binary.

→ donor; → star.

An electron-photon interaction that can be thought of as a → Compton scattering event associated with the production or destruction of an extra photon.

→ double; → Compton; → scattering.

Formation of two refracted rays of light from a single incident ray; property of certain crystals, notably calcite.

→ double; → refraction.

Same as → diplopia.

→ double; → vision.

An instability involving two layers of fluid with opposite gradients of properties. Same as → fingering instability. See also → salt finger. Double-diffusive instabilities commonly occur in any astrophysical fluid that is stable according to the → Ledoux criterion, as long as the entropy and chemical stratifications have opposing contributions to the dynamical stability of the system. They drive weak forms of convection, and can cause substantial heat and compositional → mixing. Two cases can be distinguished. In fingering convection, entropy is stably stratified (∇ - ∇ad < 0), but chemical composition is unstably stratified (∇μ < 0); it is often referred to as → thermohaline convection by analogy with the oceanographic context in which the instability was first discovered. In oscillatory double-diffusive convection, entropy is unstably stratified (∇ - ∇ad > 0), but chemical composition is stably stratified (∇μ > 0); it is related to semiconvection, but can occur even when the → opacity is independent of composition (P. Garaud, 2014, arXiv:1401.0928).

→ double;→ diffusive; → system.

Describing a → lens which is → convex on both sides.

→ doubly; → convex.

An atom that has lost two of its external electrons, for example O⁺⁺ ([O III]).

→ doubly; → ionized.

The time interval between two successive passages of the Moon through its → ascending node, 27.212 220 days (27d 5h 5 m 35.8s). Draconic month is important for predicting → eclipses. Also called draconitic month, nodical month.

Draconic, adj. of dragon, → Draco, referring to a mythological dragon for the following reason. Since an eclipse occurs when the Earth, the Sun, and a node are aligned and moreover the Moon is situated near the node, it was believed that a dragon that resided in the node swallowed the Sun or the Moon. → month.

Mâh, → month.
Gowzahri, related to gowzahr, from Mid.Pers. gowzihr "a node of the lunar orbit" [gowzihr sar ("head") = ascending node, gowzihr dumb ("tail") = descending node], also the astrological dragon, from Av. gao-ciθra- "keeping in it the seed of the ox," epithet of the Moon, since according to Iranian mythology the Moon keeps the seed/sperm of bovine animals; from gao- "cow, ox, bull" (Mod.Pers. gâv, Skt. gaus-, Gk. bous "ox," Arm. kov, O.E. cu, PIE *gwou-) + ciθra- "origin, seed, lineage" (Mod.Pers. cehr "origin"). Gowzahr was loaned into Arabic astronomical texts as jawzahr.
Gerehi, adj. of gereh→ node.

Two meteor showers with radiants in the constellation → Draco. One appears early in October and the other late in June.

Draconids, from → Draco constellation + → -ids suffix denoting "descendant of, belonging to the family of."

Eždahâyiyân, from eždahâ, → Draco, + -iyân→ -ids.

A probabilistic argument used to estimate the number of → intelligent, communicating → extraterrestrial civilizations in the → Milky Way galaxy. The Drake equation is:
N = R_* . f_p . n_e . f_l . f_i . f_c . L, where:
N = the number of → civilizations in our Galaxy with which → communication might be possible,
R_* = the average rate of → star formation in our Galaxy,
f_p = the fraction of those stars that have → planets,
n_e = the average number of planets that can potentially support → life per star that has planets,
f_l = the fraction of planets that could develop life at some point,
f_i = the fraction of planets with life that actually go on to develop intelligent life,
f_c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space,
L = the length of time for which such civilizations release detectable signals into space.
The first three terms of the equation have been successfully investigated by astronomers and are to some extent known. In contrast, values for the last four are very speculative. Drake himself estimates that N might be as high as 10,000. Carl Sagan was more optimistic, and came up with the value of a million or more for N. These estimates may be too optimistic. A pessimistic choice of parameters leads to N smaller than 1, which means that we might be the only technically sophisticated civilization in the Galaxy.

Frank Donald Drake (1930-); → equation.

A very brilliant white light which is the ignited flame of a mixture of oxygen and hydrogen projected against a block of calcium oxide (lime). Also called limelight. First working version produced by Lieutenant of the Royal Engineers, upon the Ordnance Trigonometrical Survey of Ireland (1826). It was used at night as a substitute for solar light. It was first employed in a theater in 1837 and was in wide use by the 1860s, among which in photography.

Named after Scottish engineer Thomas Drummond (1797-1840); → light.

The product of the → specific heat and → atomic weight of most solid elements at room → temperature is nearly the same. In other words, specific heat is constant for a solid and independent of temperature. Experiment shows that at moderate temperatures this law is satisfied for → crystals with rather simple structure. However, the law fails for crystals with more complex structures. More specifically the law cannot explain the variation of specific heat with temperature. The specific heat drops to zero as the temperature approaches 0 K. This behavior is explained only with the quantum theory. → Debye model.

Named after Pierre L. Dulong (1785-1838) and Alexis T. Petit (1797-1820), French chemists, who proposed the law in 1819. They collaborated in several important investigations, including studies of thermal expansion of gases and of liquids and the specific heats of substances; → law.

An act or instance of duplicating; the state of being duplicated.

Verbal noun of → duplicate.

Continuance in time; a period of existence or persistence; length of time during which anything continues.

Noun of action from L. durare "to harden," → during.

Pâyeš, noun of action from pâyidan, → last (v.).

A process of formation of → dust grains in → interstellar medium and → protoplanetary disks, in which randomly colliding aggregates may stick together.

→ dust; → coagulation.

Thermal emission in infrared from interstellar → dust grains receiving photons. Dust grains absorb ultraviolet and visible light emitted by nearby stars and re-radiate in the infrared wavelengths. Since the infrared light is of lower energy than the ultraviolet/visible light, the difference goes into heating the dust grain. Typical temperatures for interstellar grains are tens of degrees Kelvin.

→ dust; → emission.

The → absorption of → electromagnetic radiation from an astrophysical object by → dust grains associated with that object.

→ dust; → obscuration.

Tiregi, → obscuration, pat, → by; qobâr, → dust.

The process whereby a → bound system, such as a → binary system or a → globular cluster, is broken apart.

→ dynamical; → disruption.