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

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.

A combining form meaning "right" and "turning clockwise," used in the formation of compound words, e.g. → dextrorotatory, dextrocardia, dextrocular, etc. The variant dextr- occurs before vowels. Compare → levo-.

From L. dextr-, from dexter "right, right-hand;" cf. Gk. dexios "right," dexiteros "located on the right side;" Av. dašina- "right; south" ( Mid.Pers. dašn "right hand; " Ossetic dæsni "skillful, dexterous"); Skt. dáksina- "right; southern;" Goth. taihswo "right hand;" O.Ir. dess "on the right hand, southern;" PIE base *deks- "right;" + epenthetic vowel -o-; see also → south.

Râst- from râst, → right.

The clockwise rotation of the → plane of polarization of light (as viewed by an observer looking straight in the incoming light) by certain substances. See also → levorotation.

→ dextro-; → rotation.

Relating to an → optically active substance that causes → dextrorotation.

Adj. related to → dextrorotation.

A prefix meaning "two; twice; double." → dimer, → diode, → dipole, → diproton.

L. di, from Gk., → two.

To identify the nature of (an illness or other problem) by examination of the symptoms (OxfordDictionaries.com).

→ diagnosis.

1) The process of determining by examination the nature and circumstances of a diseased condition.
2) The decision reached from such an examination.
3) Scientific determination; a description that classifies a group or taxon precisely; a determining or analysis of the cause or nature of a problem or situation (Dictionary.com).

L., from Gk. diagnosis "a discerning, distinguishing," from stem of diagignoskein "discern, distinguish," literally "to know thoroughly," from dia- "through" + gignoskein "to learn," cognate with Pers. šenâs-, šenâxtan "to know, to be acquinted" and dânestan "to know," as below, ultimately from PIE root *gno- "to know."

Parnâs, from par- "through," + nâs "to know," as in Zazaki nâs- "to know," Kurd. nâs-, nâsîn "to know," related to Pers. šenâs- "to know," related to šenâxtan, → knowledge and dânestan, → science.

1a) Of, relating to, or used in → diagnosis.
1b) Serving to identify or characterize; being a precise indication.
2a) Diagnosis.
2b) A symptom or characteristic of value in diagnosis.
2c) A message output by a computer diagnosing an error in a computer program, computer system, or component device; a program or subroutine that produces such messages (Dictionary.com).

From Gk. diagnostikos "able to distinguish," → diagnosis.

→ diagnosis.

In a → polygon, a line segment joining any two non-adjacent vertices (→ vertex).

From M.Fr. diagonal, from L. diagonalis, from diagonus "slanting line," from Gk. diagonios "from angle to angle," from dia- "across, dividing two parts" + gonia "angle," related to gony "knee," L. genu "knee," Mod.Pers. zânu "knee," Av. žnav-, žnu- "knee," Skt. janu-; PIE base *g(e)neu-, see below.

Tarâkonj, from tarâ- "across, through," → trans-, + konj "angle, corner, confined place" (variants xong "corner, angle," Tabari kânj, Kurd. kunj, Hamadâni kom), maybe from the PIE base *g(e)neu-, as above, and related to Mod.Pers. zânu "knee" (Av. žnu-), Skt. kona- "angle, corner," Gk. gony, gonia, L. cuneus "a wedge," Albanian (Gheg dialect) kân "angle, corner," Albanian (Toks) kënd "angle, corner."

A graphic representation of the behavior of one or several variables.

From Fr. diagramme, from L. diagramma, from Gk. diagramma "that which is marked out by lines," from diagraphein "to mark out by lines," from dia- "across, out" + graphein "to write, draw," → -graphy.

Nemudâr agent noun of nemudan "to show," → display, from the past stem nemud + -âr, such as xâstâr, foruxtâr, padidâr, parastâr (contraction of *parastidâr).

Relative to or characterized by → diamagnetism.

→ diamagnetism.

The property of a substance, like bismuth, that creates a weak magnetic field in opposition of an externally applied magnetic field, thus causing a repulsive effect. In diamagnetic materials the → magnetic moments of individual atoms are not permanent. Within each atom the electron spins and orbital motions all exactly balance out, so any particular atom has no net magnetic moment. The external magnetic field generates little currents by induction. According to → Lenz's law, the induced magnetic moments of the atoms are directed opposite to the magnetic field.

Diamagnetic, from Gk. dia- a prefix used with several meanings "passing through; thoroughly; completely; going apart," and in the present case "opposed;" → magnetic. magnetic.

Pâdmeqnât, from pâd- "against, contrary," → anti-, + megnât→ magnetism.

Any chord passing through the center of a figure. The length of this chord.

O.Fr. diamètre, from L. diametrus, from Gk. diametros "diagonal of a circle," from dia- "across, through" + metron "a measure" → meter.

Tarâmun, from tarâ- "across, through," → trans- + mun/mân "measure," as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl," from O.Pers./Av. mā(y)- "to measure," cf. Skt. mati "measures," matra- "measure," Gk. metron "measure," L. metrum; PIE base *me- "to measure."

A crystalline form of → carbon, which is the hardest substance known. Each carbon in a diamond crystal is bonded to four other carbon atoms forming a tetrahedral unit. This tetrahedral bonding of five carbon atoms forms an incredibly strong molecule. Diamond has a very high → refractive index and → dispersive power. It is colorless when pure, and sometimes colored by traces of impurities. Natural diamond was formed billions of years ago within the Earth → mantle at depths greater than 150 km, where pressure is roughly 5 giga→ pascals and the temperature is around 1200 °C. Diamonds reach the surface of the Earth via volcanic eruptions. Similarly very small diamonds (micrometer and nanometer sizes) are usually found in impact sites of → meteorites. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. When diamond is exposed to high temperatures or ion bombardment, it will be transformed into → graphite.

Diamond, from O.Fr. diamant, from M.L. diamant-, diamas-, from L. adamant-, adamas "hardest metal," from Gk. adamas "unbreakable," from → a- "not" + daman "to subdue, to tame;" cognate with Pers. dâm "a tame animal."

Almâs, loanword from Gk., as above.

An intense flash of light that happens a few seconds before and after totality during a solar eclipse. The effect is caused by the last rays of sunlight before totality (or the first rays of sunlight after totality) shining through valleys on the edge of the Moon.

→ diamond; → ring; → effect.

Oskar, → effect; angoštar "a ring worn on the finger," from angošt "finger," Mid.Pers. angušt "finger, toe," Av. angušta- "toe," from ank- "curved, crooked," cf. Skt. angustha- "thumb," ankah "hook, bent," Gk. angkon "elbow," angkura "anchor," L. angulum "corner" (E. angle), Lith. anka "loop," O.E. ancleo "ankle," O.H.G. ango "hook," PIE base *ang-/*ank- "to bend"; → diamond.

A device with a restricted aperture, located in an optical system at any of several points, that cuts off marginal light rays not essential to image formation.

From L.L. diaphragma, from Gk. diaphragma "partition, barrier," from diaphrassein "to barricade," from dia- "across" + phrassein "to fence or hedge in."

Miyânban, from miyân "middle, interior, between" (Mid.Pers. miyân "middle," Av. maiδya-, maiδyāna- "medium, middle," cf. Skt. mádhya- "middle, intemediate," Gk. mesos "middle," L. medius "middle," Goth. midjis, O.E. midd "middle," O.C.S. medzu "between," Arm. mej "middle," PIE *medhyo- "middle," , from base *me- "between") + band "barrier, shutter," from bastan "to bind, shut" (Mid.Pers. bastan/vastan "to bind, shut," Av./O.Pers. band- "to bind, fetter," banda- "band, tie," cf. Skt. bandh- "to bind, tie, fasten," PIE *bhendh- "to bind").

1) General: A division in two parts or kinds that differ widely from or contradict each other.
2) Astro.: The phase of the Moon or a planet when half of its surface appears illuminated by the Sun.

From Gk. dichotomia "cutting in two," from dicho- "apart, in two," combining form of dicha "in two, asunder," akin to → di-, + temnein "to cut."

Dopâregi, from do→ two + pâré "piece, part, portion, fragment" (Mid.Pers. pârag "piece, part, portion; gift, offering, bribe;" Av. pāra- "debt," from par- "to remunerate, equalize; to condemn;" PIE *per- "to sell, hand over, distribute; to assign;" cf. L. pars "part, piece, side, share," portio "share, portion;" Gk. peprotai "it has been granted;" Skt. purti- "reward;" Hitt. pars-, parsiya- "to break, crumble") + -(g)i a noun/state suffix.