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

A system of evolved → binary stars in which both → components have ejected their envelopes and evolve toward → white dwarf stage. So far a half dozen double-degenerate → binary systems are known, for example Henize 2-248 (M. Santander-Garcia et al., 2015, 518, 5).

→ double; → degenerate; → binary; → system.

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.

A → spectroscopic binary in which the → spectral lines of both stars are seen and the lines are alternatively double and single. Same as → SB2 binary. See also: → single-lined binary.

→ double; → line; → binary

A → double-lined spectroscopic binary whose → light curve is typical of an → eclipsing binary.

→ double; → line; → eclipsing; → binary.

Same as → double-lined binary.

→ double; → line; → spectroscopic; → binary.

A → galaxy that emits radio energy from two regions located on opposite sides of the galaxy.

→ double; → lobe; → radio; → source.

An experiment of → diffraction and → interference of two light beams using a → double slit; → Young's experiment.

→ double; → slit; → experiment.

A pair of forbidden spectral lines of the same atom arising from a common upper excitation level, for example [O III] λ 5007 and [O III] λ 4959, [N II] λ 6584 and [N II] λ 6548, and [S II] λ 6717, [S II] λ 6731.
A pair of associated lines arising from transitions having a common lower energy level in a spectrum characteristic of the alkali metals.

From O.Fr. doublet, from → double + -et diminutive suffix.

Dotâyé, from dotâ→ double + -(y)é nuance suffix.

1) To a double measure or degree.
2) In a double manner. → doubly convex, → doubly ionized, → doubly refracting crystal.

→ double; → -ly (; → twice).

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.

A → transparent → crystalline substance (such as calcite, quartz, and tourmaline) that is → anisotropic relative to the → speed of light. A ray incident normally on such crystals is broken up into two rays in traversing the crystal, → ordinary ray and → extraordinary ray.

→ doubly; → refracting; → crystal.

1) A feeling of uncertainty about the truth, reality, or nature of something. → skepticism.
2) To be uncertain about; consider questionable or unlikely; hesitate to believe (Dictionary.com).

M.E. douten, from O.Fr. douter "doubt, be doubtful," from L. dubitare "to doubt, question, hesitate" (related to dubius "uncertain"), from duo, "→ two," + habere "have, hold," with a sense of "of having two minds, undecided between two things;" cf. Pers. dodeli, as below.

Gomân, from Mid.Pers. gumân "doubt;" ultimately from Proto-Ir. *ui-man-, from suffixed *man- "to think," → idea.
Šakk, loan from Ar.
Dodeli, literally "having two minds," from do, → two, + del, → heart (also meaning "soul, spirit, will, desire, courage, mind"); cf. Sogdian δβanā (from *dwa-nā), Ger. Zweifel, and L. dubius, as above.

Toward or in a lower physical position.
See also: → download, → downgrade, → upload, → downsizing, → meltdown, → overload, → spin-down, → top-down structure formation.

M.E. doun, from O.E. dune "downward," short for adune, ofdune, from a-, of "off, from" + dune "hill."

Pâyin "bottom, below; at the foot of," from pâ(y) "foot; step;" Mid.Pers. pâd, pây; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-.
Foru "down, downward; below, under, beneath; low," Mid.Pers. frôt "down, downward;" O.Pers. fravata "forward, downward;" Skt. pravát- "a sloping path, the slope of a mountain."

1) A downward slope, especially of a road.
2) To assign to a lower status; to minimize the importance of (Dictionary.com).

→ down; → grade.

1) To transfer data from any other computer to one's computer.
2) The act of downloading.

→ down; → load.

Bârgereftan, literally "to take load," from bâr, → load, + gereftan "to take," → receiver; bârgiri, verbal noun of bârgereftan.

A scenario of galaxy formation whereby massive galaxies formed earlier in the history of the → Universe (i.e. at high → redshifts) and completed their → star formation process more rapidly than low-mass galaxies. This scenario contrasts with what might be expected from simple → hierarchical structure formation scenarios, which predict that large galaxies formed in more recent times through the → merging of small galaxies.

Downsizing, first suggested by Cowie et al. (1996, AJ 112, 839), from downsize (v.), is a new sense for this term. Its current main meaning in non astrophysical contexts is "to make in a smaller size, or become smaller in size (in particular in economic vocabulary, by reductions in personnel)," from → down + → size.

Bozorg-bé-kucak, literally "large to small," from bozorg, → large, +bé "to" + kucak, → small.

1) With or in the direction of the current of a stream. → upstream.
2) Of or pertaining to the latter part of a process or system.

→ down; → stream.

Forud, → incidence; water, → water.

A → white dwarf whose spectrum shows carbon features of any kind.

D short for → dwarf; Q a convention; → white.

The Dragon. A large constellation that winds around the north → celestial pole, appearing to encircle → Ursa Minor. The north → ecliptic pole also lies within Draco. Abbreviation: Dra, genitive form: Draconis.

O.Fr. dragon, from L. draco "serpent, dragon," from Gk. drakon "serpent, seafish," from drak-, strong aorist stem of derkesthai "to see clearly," perhaps literally "the one with the (deadly) glance," cf. Av. darəs- "to look," huuarə.darəsa- "having the appearance of the sun," Skt. darś- "to see, appear, look, show," dárśya- "worthy of being seen;" PIE base *derk- "to look."

Eždahâ, from Mid.Pers. aždahâg, ažidahâk, from Av. aži.dahāka- "the name of an evil king in the Iranian mythology," from aži- "serpent; dragon, monster" (Mid.Pers. až, âž, aži), cf. Skt. áhi- "snake, adder," Gk. ékhis, óphis "snake," L. anguis "snake," Arm. auj, Russ. už, Lith. angis; PIE base *ang^w(h)i- "snake, worm." The etymology of the second component, Av. dahāka-, is a matter of discussion. It is probably related to dahaka- "stinging, tormenting," from dah- "to sting, to do harm."