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

The fusion of a deuterium nucleus with a proton which produces the lightest isotope of helium: D + H → ³He + γ. Deuterium burning occurs in stellar cores at a temperature exceeding 10⁶ K. The onset of deuterium burning marks the end of the → protostellar collapse. It is the only → nuclear reaction that occurs in → brown dwarfs. In normal stars, it is the second step in the → proton-proton chain which leads to the formation of ⁴He, allowing stars to arrive on the → main sequence.

→ deuterium; → burning.

The → enrichment of deuterium (D) with respect to → hydrogen (H) in → Solar System molecules when compared with the D/H ratio in the → interstellar → solar nebula. H-bearing molecules in → comets, → planets, and → chondrite  → meteorites show a systematic D enrichment relative to the → molecular hydrogen of the solar nebula. Because there is no nuclear source for D in the Universe, the observed → isotopic enrichment must have its origin in chemical reactions having faster reaction rates for D than for H. In the Solar nebula the → isotopic fractionation of D between → water and H followed the reversible reaction:
H₂O + HD ⇔ HDO + H₂.
At low temperatures, this reaction favors the concentration of D in HDO. In the → interstellar medium grain chemistry plays a crucial role in D enrichment. See also → enrichment factor.
Apart from → deuterium fractionation, D could be enriched through another mechanism. Since molecular hydrogen (H₂) is more → volatile than molecular deuterium (D₂), D/H ratio could increase in certain planets that orbit near their star.

→ deuterium; → enrichment.

The ratio between the D/H value in → water and in → molecular hydrogen, as expressed by:
f = [(1/2)HDO/H₂O]/[(1/2)HD/H₂] = (D/H)_H2O/(D/H)_H2.
When f> 1, there is → deuterium enrichment.

→ deuterium; → enrichment; → factor.

The difference between the deuterium (D)/hydrogen (H) → abundance → ratio in an object with respect to that representing a standard or mean value for that type of objects. Same as → isotope fractionation of deuterium. In the gas phase chemistry many of the D fractionation reactions produce an excess of D atoms relative to → hydrogen atoms. Deuterium fractionation in → interstellar cloud cores, → protostars, and → Solar System bodies is frequently used to infer important aspects of their physical and chemical histories. For example, the → deuterium enhancement in the Earth's sea water, with respect to the cosmic abundance, has been interpreted as being due to → enrichment by → comet-like → planetesimals colliding with the young Earth.

→ deuterium; → fractionation.

A nucleus of a deuterium atom (a combination of a proton and a neutron).

From Gk. deutero-, combining form of deuterios "second" + -ion a suffix used in the names of subatomic particles.

1) To elaborate or expand in detail, for example a theory.
2) To bring to a more advanced or effective state.
3) Math.: To express in an extended form, as in a → series. → developed turbulence, → development.

From M.Fr. développer, O.Fr. desveloper, from des- "undo" prefix + veloper "wrap up," of unknown origin.

Govâlidan, from Proto-Iranian *vi-uar, cf. Skt. vi-vardh- "to grow up; to blossom," Av. *vi-varəd-, from Skt./Av. prefix vi- "out, apart" + varəd- "to increase, augment, strengthen, cause to prosper," Mid.Pers. vâlitan, Mod.Pers. bâlidan "to grow, to wax great."

A regime of → turbulence characterized by a high → Reynolds number, showing many general aspects that are common to different flows (statistical symmetries, persistent dissipation, energy cascade, → intermittency). Despite those universal features, the understanding of developed turbulence remains as one of the greatest unsolved conceptual problems, on the borderline between mathematics and physics, with numerous ramifications from astrophysics through meteorology to engineering.

Developed, p.p. of → develop; → turbulence.

1) The act, process, or result of developing. The state of being developed.
2a) Math.: The act or process of → expanding an expression into another of equivalent value or meaning.
2b) The equivalent expression into which another has been developed.

From → develop + -ment suffix forming nouns from verbs.

Govâleš, from govâl, stem of govâlidan, → develop, + -eš verbal noun suffix, → -tion.

1) (v. intr.) To turn aside, as from a way, course, etc. By extension, to depart from a course of action or acceptable norm.
2) (v.tr.) To cause to turn aside. → deviation, → standard deviation.

From L.L. deviatus "turned from the straight road," p.p. of deviare, from → de- + via "road," + -ate.

1) Kažraftan, from kaž "crooked, bent, being aside" (cf. Skt. kubja- "hump-backed, crooked," Pali kujja- "bent," L. gibbus "hump, hunch," Lith. kupra "hump") + raftan "to go, walk, proceed" (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").
2) Kažrâh kardan, from kaž, as above, + râh "way, path" (Mid.Pers. râh, râs "way, street," from *rāθa-, cf. Av. ratha- "chariot," akin to Skt. rathah "car, chariot," L. rota "wheel," rotare "revolve, roll," Lith. ratas "wheel," O.H.G. rad, Ger. Rad, Du. rad, O.Ir. roth; PIE *roto- "to run, to turn, to roll") + kardan "to do, to make," Mid.Pers. kardan, O.Pers./Av. kar- "to do, make, build," Av. kərənaoiti "makes," cf. Skt. kr- "to do, to make," krnoti "makes," karma "act, deed;" PIE base k^wer- "to do, to make."

The act of deviating; departure from a standard or norm.
Statistics: The difference between a datum and some reference value, typically the mean of the data. → standard deviation.

Verbal noun form of → deviate.

Something, thought out, invented, or adapted, for a special purpose.
Assembly of parts or pieces in one body to perform a work, observe a phenomenon, or for measuring.

From O.Fr. devis "division, separation, disposition, wish," from L. divisus, p.p. of dividere "to divide," → divide.

Dastgâh "means, implement, apparatus," originally "wealth, splendour," from dast "strength, superiority," originally "hand" (Mid.Pers. dast, O.Pers. dasta-, Av. zasta-, cf. Skt. hásta-, Gk. kheir, L. praesto "at hand," Arm. jern "hand," Lith. pa-žastis "arm-pit;" PIE *ghes-to-) + gâh "place, time," O.Pers. gāθu-, Av. gātav-, gātu- "place, throne, spot" (Skt. gâtu- "going, motion; free space for moving; place of abode," PIE *gwem- "to go, come").

An evil spirit; demon. → dust devil.

M.E. devel, from O.E. deofol, from L.L. diabolus, from Gk. diabolos, literally, "slanderer," from diaballein "to throw across, slander," from dia- "across, through" + ballein to "throw."

Div "devil, demon" (Mid.Pers. dêw; O.Pers. daiva- "evil god, demon;" Av. daēva- "evil spirit, false god;" Skt. deva-; Gk. Zeus "supreme god;" L. deus "god;" PIE base *deiwos "god," from *dei- "to gleam, to shine").

To apply or dedicate (oneself, time, money, etc) to some pursuit, cause, etc. (Dictionary.com).

From L. devotus, p.p. of devovere "dedicate by a vow, sacrifice oneself, promise solemnly," from → de- "down, away" + vovere "to vow," from votum "a promise to a god, solemn pledge, dedication; that which is promised; a wish, desire, prayer," from PIE root *wegwh- "to speak solemnly, vow, preach;" cf. Skt. vaghat- "one who offers a sacrifice;" Gk. eukhe "vow, wish."

Âdaxtan, on the model of pardâxtan (among several meanings) "to devote, consecrate, to be busily and attentively engaged; to attempt, care about; to employ" (Steingass), with prefix â- and stem âxt, âz- (→ theoretician).

1) Profound dedication; consecration.
2) Earnest attachment to a cause, person, etc. (Dictionary.com).

Verbal noun of → devote.

1) Water condensed onto grass and other objects near the ground, the temperatures of which have fallen below the dewpoint of the surface air due to radiational cooling during the night, but are still above freezing.
2) Moisture in small drops on a surface.

O.E. deaw, from P.Gmc. *dawwaz, O.H.G. tow, Gk. thein, "to run," thoos "quick," PIE base *dheu- "to run, flow" (cf. Pers. dav-, davidan "to run," Skt. dhav- "to run, flow," dhavati "flows, runs").

Šabnam, from šab→ night + nam "moisture; dew; wet," Mid.Pers. namb, nam, Av. napta- "moist," nabas-câ "cloud," nabah- "sky," Skt. nábhas- "moisture, cloud, mist, sky," Gk. nephos "cloud," L. nebula "mist," PIE base *nebhos- "moisture, cloud, mist."

A hollow tube that extends out in front of the objective lens (refractors) or corrector lens (Schmidt-Cassegrains). It shields the exposed optics from wide exposure to the cool ambient air, slowing heat loss and preventing dew formation. Reflector telescopes do not need dew caps because the main mirror rests at the bottom of the tube, which acts as a dew shield.

→ dew + cap, from O.E. cæppe "hood, head-covering," from L.L. cappa "a cape, hooded cloak."

Kolâhak, from kolâh "cap," see below, + similarity suffix -ak. Kolâh "cap," cf. L. celare "to hide, conceal," occulere "to dissimulate," Gk. kalyptein "to cover," kalia "hut, nest," Skt. cala "hut, house," Goth. hilms "helmet," huljan "cover over," hulistr "covering," E. hull "seed covering," from O.E. hulu, from O.H.G. hulla, hulsa, O.E. hol "cave;" PIE base *kel- "conceal." Šabnam→ dew.

The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur.

→ dew; → point.

Insulated bottle containing a cryogenic fluid. The electronic detectors operated at very low temperature are mounted inside a dewar.

Named after its inventor Sir James Dewar (1842-1923), Scottish chemist and physicist.

A rainbow formed in the small drops often found on grass in early morning. While the name implies that those drops are dew, that is probably rarely the case. Rather, the drops are usually the result of guttation (the water exuded from leaves as a result of root pressure) rather than dew.

→ dew; → bow.

A conventional notation for decimal exponent, which converts the number after it into its common antilogarithm; for example, dex (2.35) = 10^2.35.

From decimal + exponent.