An Etymological Dictionary of Astronomy and Astrophysics
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A long, dark structure located close to the → Galactic plane and occupying an area between longitudes l ~15° and ~35° and latitudes b ± 10° in the constellations Aquila, Serpens, and eastern Ophiuchus. The Aquila Rift is a complex of dust and → molecular clouds making part of → Gould's Belt in the → Orion Arm. The mass of the molecular gas, derived from → carbon monoxide (CO) observations (Dame et al. 2001, ApJ 547, 792), is in the range ~ 1-3 x 10⁵ → solar masses. A distance of ~260 pc has been estimated for the Aquila Rift, but it is uncertain. Recent Herschel observations have revealed a filamentary structure in the Aquila Rift and the presence of a population of → pre-stellar cores as well as → young stellar objects (André et al. 2010, A&A 518, L102; Bontemps et al. 2010, A&A 518, L85; Könyves et al. 2010, A&A 518, L106).

→ Aquila; → rift.

A hypothesis proposed by Alfred Wegener (1912) suggesting that the → continents are not stationary, but drift through time. Wegener's hypothesis has since been developed and included in a new theory called → plate tectonics.

→ continental; → drift.

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.

1) The hypothetical motion of the supposed → ether relative to the Earth. The → Michelson-Morley experiment found no ether drift. An analogy is given by a boat drifting in a fast-flowing river due to the river's current. With the same power, the speed would be slower when sailing across the stream. Moreover, in order to reach directly opposite the starting point, the boat would have to be headed somewhat upstream. See also the → ether drag.
2) The motion of the Earth relative to the → rest frame defined by the → cosmic microwave background radiation.

→ ether; → drift.

An undesired progressive change in an oscillator's frequency with time.

→ frequency; → drift.

An apparent fissure in the bright clouds of the Milky Way between → Cygnus and → Sagittarius caused by a series of large, dark, overlapping clouds.

→ great; → rift.

The apparent slow motion of the → radiant of a → meteor shower from night to night against the background stars due to the Earth moving in its orbit around the Sun.

→ radiant; → drift.

1) General: a gap or break made by splitting, cleaving, etc.; fissure; cleft.
2) Geology: A narrow cleft, fissure, or other opening in rock, made by cracking or splitting.
3) Geology: An elongated trough in the Earth's crust bounded by → faults.

M.E., from a Scandinavian source; cf. Dan., Norw. rift "a cleft."

1) Câk "fissure, rupture, cleft, crack," related to caqidan "to drive a nail, strike together, fix a spike;" caxidan "to quarrel, strive;" diatectal Shughni cuγ, Roshani coγ "breaking, tearing, ripping up;" Malâyeri ceqidan "cracking of a cold porcelain bowl when receiving hot water;" Yazghulami cok-, coxt "to pound, to stamp;" Wakhi cuk-, cukt "to strike;" Ossetic cædyn "to shake, strike iron;" Lori cok "a mark fixed to separate two grounds;" Sogd. cax "to battel, fight;" Mid.Pers. (prefixed) pacên "copy" (see also Cheung 2007). Gosal-darré, from gosal, → fault, + darré, → valley.

A long, narrow valley formed by the lowering of land between two → faults. Also called → graben.

→ rift; → valley.

A mound or bank of snow deposited as sloping surfaces and peaks, often behind obstacles and irregularities, due to eddies in the wind field.

→ snow; → drift.

Barf-rând "snowdrift, drfited snow" from barf, → snow, + rând "driving, drfit; drifted," 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"); barf-e bâd âvard "snow brought by wind," from barf + bâd→ wind + âvard, short for âvardé "brought," p.p. of âvardan "to bring; to cause, produce" (Mid.Pers. âwurtan, âvaritan; Av. ābar- "to bring; to possess," from prefix ā- + Av./O.Pers. bar- "to bear, carry," bareθre "to bear (infinitive)," bareθri "a female that bears (children), a mother;" Mod.Pers. bordan "to carry;" Skt. bharati "he carries;" Gk. pherein; L. fero "to carry").

The relative motion of two groups of stars in the Galaxy moving in opposite directions.

→ star; → drift.