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

A dwarf elliptical galaxy that is a satellite of our Galaxy and lies at a distance of about 250,000 light-years from the Galactic center. Its diameter is only about 3,500 light-years, and its absolute magnitude -8.6, making it the least luminous galaxy known.

→ Draco; → dwarf.

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.

1) General: The act of dragging or the state of being dragged.
2) Fluid mechanics: The → force that opposes the relative motion of an object through a → fluid. In → aeronautics, the component of aerodynamic force parallel to the relative wind tending to reduce the forward motion of the airplane. See also → lift; → thrust.
3) To pull or be pulled with force, especially along the ground or other surface.

From O.N. draga, O.E. dragan "to draw," from P.Gmc. *dragan "to draw, pull," from PIE base *dhragh- "to draw, drag on the ground" (cf. Skt. dhrajati "pulls, slides in," L. trahere "to pull," Rus. drogi "wagon."

Kerr, kerré, kerridan "drag," cf. Laki keronen, Hamadâni kerândan "to pull along, drag," Tâleši kernye, Tabari kərəš "to drag;" Lori, Hamadâni kerr "line, scratch;" related to Mid/Mod.Pers. kešidan, kašidan "to draw, protract, trail, drag, carry;" kâštan, keštan, kâridan "to cultivate, to plant, to make furrows;" Av. kar- "to strew seed, cultivate," kāraiieiti "cultivates," karš- "to draw (a furrow), till, plant;" cf. Skt. kar- "to scatter, strew, pour out," kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base k^wels- "to plow."
Vârâné, from vâ-, opposition prefix, → de-, + râné, from rândan "to push, drive, cause to go" (causative of raftan "to go, walk, proceed," present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").

A unit used to express the strength of → far ultraviolet (FUV) average → interstellar radiation field. It is equal to ~ 1.7 → Habing field.

Named after B. T. Draine, 1978, ApJS 36, 595.

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 process by which the nucleosynthesis products inside a star are drawn to upper layers of the star. → first dredge-up; → second dredge-up; → third dredge-up.

From M.E. (Scots) dreg-, O.E. draeg- (in drægnet "dragnet"), akin to dragan "to draw" + up.

Birunkašid, past stem of birun kašidan, from birun "out, the outside" (Mid.Pers. bêron, from bê "outside, out, away" + rôn "side, direction," Av. ravan- "(course of a) river") + kašidan "to draw," Mid.Pers. kašitan, Av. karš- "to draw," Skt. kars-, kársati "to pull, drag, plough," Gk. pelo, pelomai "to be busy, to bustle."

A pre-Colombian Maya manuscript consisting of numerous calendar and astronomical data, probably dating from the 12th century. It seems that it is an updated copy of a document from the period of the old Maya Empire (4th-9th centuries). It contains a table which covers over 32 years, grouping 45 successive → lunations, divided into 69 groups of 5 or 6 lunations. The data are calculated in days and correspond remarkably to the intervals in an eclipse table: each group ends at the probable date of a solar eclipse (M.S.: SDE).

Dresden refers to the Dresden Library where the original document is preserved. It was bought in 1739 by the library director, Johann Christian Götze, who found it in a private library in Vienna. Its earlier history is unknown; codex, from L. codex earlier caudex "book, book of laws," literally "tree-trunk, book (formed originally from wooden tablets);" → codex.

1a) General: A driving movement or force; impulse; impetus; pressure.
1b) Physics: A slight change of a quantity with time, for example the sensitivity of an electronic detector continuously operated during a long period as an effect of continued use.
1c) A slow change in frequency of a radio transmitter.
1d) Aerospace: The gradual deviation of a rocket or guided missile from its intended trajectory.
2) (v.intr.) To be carried along by currents of water or air, or by the force of circumstances.

From M.E. drift, from O.E. drifan "to drive," or from O.N. or M.Du. drift, from P.Gmc. *driftiz, related to *dribanan "to drive."

Delek from Lori, Laki, Hamadâni, Malâyeri "push, shove, drive;" variants Gilaki duko, Tâleši dako, Baluchi dhakkk(a) "push, shove, blow," Choresmian dh- "to hit," Kurd. dân/di- "to beat, hit," Proto-Iranian *daH- "to beat, hit, strike" (Cheung 2007); PIE base *dhen- "to hit, push;" delekidan, verb from delek.

In radio astronomy, the output response as a function of position for a given filter as the source passes through the beam.

→ drift; → curve.

The amount of drift, in any of its several senses, per unit time.

→ drift; → rate.

The average velocity of a charged particle in a plasma in response to an applied electric field.

→ drift; → velocity.

1a) To cause to move, to force to act. → continuum-driven wind, → dust-driven wind, → line-driven wind, → radiation-driven implosion, → radiation-driven mass loss, → radiation-driven wind.
1b) To cause and → guide the → motion of a → telescope.
2a) The act of driving.
2b) The → mechanism that imparts or transfers → power to a telescope so that it can move. → alpha drive, → delta drive, → drive accuracy, → slewing drive .

M.E. driven; O.E. drifan; cf. O.N. drifa, Goth. dreiban.

Rândan "to cause to go," causative of raftan "to go, walk, proceed" (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").

The accuracy with which a telescope is moved by alpha or delta drives.

→ drive; → accuracy.

Very small, numerous, and uniformly distributed water drops that may appear to float while following air currents. Unlike fog droplets, drizzle falls to the ground.

Drizzle, dryseling "a falling of dew," from M.E. drysning, related to dreosan "to fall," cf. O.S. driosan, Goth. driusan.

Narmé bârân literally "smooth rain," from narmé, from narm "soft; smooth; mild," Mid.Pers. narm + bârân, → rain.

1a) A small quantity of liquid that falls or forms in a round or pear-shaped mass.
1b) A very small quantity of liquid; a very small quantity of anything.
2) To fall in small portions, as water or other liquid.

M.E. drop(e), from O.E. dropian; related to O.H.G. triofan, Du. drop, Ger. Tropfen.

Cekké, cekidan "drop; small, minute," cekidan "to drop."

A very small drop of a liquid.

→ drop + diminutive suffix let.

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.

1) Lacking moisture; not damp or wet.
2) Having little or no rainfall.

M.E. drie; O.E. dryge; cf. M.L.G. dröge, M.Du. druge, Du. droog, O.H.G. trucchon, Ger. trocken.

Xošk "dry;" Mid.Pers. xušk "dry;" O.Pers. uška- "mainland;" Av. huška- "dry;" cf. Skt. śuska- "dry, dried out;" Gk. auos "dry, dried up;" O.E. sēar "dried up, withered;" Lith. sausas "dry, barren."

A merger between → gas-poor  → early-type galaxies.

→ dry; → merger.