An Etymological Dictionary of Astronomy and Astrophysics

Of, pertaining to, or noting two; having a twofold, or double, character or nature.

Etymology (EN): From L. dualis, from duo “two.”

Etymology (PE): Dogâné, from do “two,” cognate with duo + -gân plurality suffix + -é nuance suffix.

The outcome of a → merger process between two galaxies, each with its own central → supermassive black hole (SMBH), resulting in a remnant galaxy hosting two SMBHs. Simulations of → galaxy mergers show there should be lots of dual → active galactic nuclei (AGN) visible at less than 10 kpc separations. As of 2015 more than 100 known dual supermassive black holes have been found. See also → binary supermassive black hole.

See also: → dual; → supermassive; → black; → hole.

1. Philo.: The doctrine, as opposed to idealism and materialism, that reality consists of two basic types of substance usually taken to be mind and matter or two basic types of entity, mental and physical.
   

   2. The state of being twofold or double. → dualism, → pluralism (Dictionary.com).

See also: → dual; → -ism.

The quality or character of being twofold, as the → wave-particle duality.

Etymology (EN): M.E dualitie, from L.L. dualitas.

Etymology (PE): Dogânegi, from dogânag + -i.

The second brightest star in the constellation → Ursa Major with a → visual magnitude of about 1.8. It lies at the front of the → Big Dipper’s bowl and with → Merak (Beta UMa) makes the famous → Pointers. α Ursae Majoris is a → supergiant of type K0 IIIa and has a → companion.

Etymology (EN): From Ar. al-dubb (الدب) “bear,” referring to the bear in Gk. mythology.

Etymology (PE): Dobbé from Ar., as above.

Describing a substance that exhibits → ductility.

Etymology (EN): M.E., from L. ductilis, from duct(us), p.p. of ducere “to draw along,” → aonduct, + -ilis “-il,” a suffix of adjectives.

Etymology (PE): Rešâyand, literally “capable of becoming string, thread,” from reš, as in rešté “thread, line, rope, row,” rešmé “string, rope, thread,” variants rasan, ras, (Gilaki) viris, related to abrišam
“silk;” from reštan, risidan “to spin;” Mid.Pers. rištag “rope, string, thread;” Av. uruuaēs- “to turn around,” uruuaēsa- “vortex in water;” Proto-Iranian *uris- “to turn, spin;” cf. Skt. vréśī- “an appellation of waters;” Gk. rhiknos “crooked;” Lith. rišti “tie, bind;” O.H.G. rīho “knee-bend;” âyand agent noun form of âmadan “to come; to become,” → elastic.

The property of a metal that allows it to be elongated into wire or threads without fracture. For example, → copper and → silver are highly ductile metals.

See also: → ductile; → -ity.

The product of the → specific heat and → atomic weight of most solid elements at room → temperature
is nearly the same. In other words, specific heat is constant for a solid and independent of temperature. Experiment shows that at moderate temperatures this law is satisfied for → crystals with rather simple structure. However, the law fails for crystals with more complex structures. More specifically the law cannot explain the variation of specific heat with temperature.
The specific heat drops to zero as the temperature approaches 0 K. This behavior is explained only with the quantum theory. → Debye model.

See also: Named after Pierre L. Dulong (1785-1838) and Alexis T. Petit (1797-1820), French chemists, who proposed the law in 1819. They collaborated in several important investigations, including studies of thermal expansion of gases and of liquids and the specific heats of substances; → law.

One of the brightest planetary nebulae; it lies in the constellation
→ Vulpecula at a distance of about 1000 light-years. It was discovered by Charles Messier in 1764.

Etymology (EN): Dumbbell “a short bar with weights at each end that is used for exercise,” from dumb + bell.
When viewed in a small telescope, the brighter portion of the nebula shows like a bipolar geometry, hence the name; → nebula.

Etymology (PE): Dambel loanword from dumbbell, as above; → nebula.

Consisting of twelve → years.

Etymology (EN): From L. duodecennium, from duodecim “tweleve,” from duo, → two, + decem, → ten, + annus “year,” → annual.

Etymology (PE): Davâzdahsâli, from davâzdah “twelve,” from do,
→ two, + dah, → ten + sâl, → year.

A → lunisolar calendar in which the years are named after each of the following twelve animals: rat, ox, tiger, hare, dragon, snake, horse, sheep, monkey, cock, dog, pig. An animal presides over one year in the twelve-year cycle, which is then repeated. The calendar was/is mainly used by central Asian cultures (Khotanese, Sogdians, Buddhists, Kucheans, Mongols, and Chinese). It was also used in Iran after the Mongol invasion in the thirteenth century.

See also: → duodecennial; → animal; → calendar.

1. To make an exact copy of.
   

2. A copy exactly like an original.

Etymology (EN): From L. duplicatus, p.p. of duplicare
“to double,” from duo, → two + plicare “to fold,” → multiply.

Etymology (PE): Dotâyidan, “to double,” infinitive from dotâyi, → double.

An act or instance of duplicating; the state of being duplicated.

See also: Verbal noun of → duplicate.

The ability to withstand damage or decay.

See also: → durable; → -ity.

Capable of lasting, enduring; withstanding deterioration.

See also: → duration; → -able.

Continuance in time; a period of existence or persistence; length of time during which anything continues.

Etymology (EN): Noun of action from L. durare “to harden,” → during.

Etymology (PE): Pâyeš, noun of action from pâyidan, → last (v.).

In the course of, in the time of, throughout the continuance of.

Etymology (EN): M.E. Duryng, durand, pr.p. of duren “to last, endure, continue, be or exist,” from O.Fr. durer, from L. durare “to harden,” from durus “hard;” PIE root *deru- “be firm, solid, steadfast.”

Etymology (PE): Tarpây, literally “lasting over time,” from tar- “through, across, over time,” variant tarâ-, → trans-, + pây present stem and agent noun of pâyidan, → last (v.).

The time of day immediately following → sunset which is partial darkness between day and night.

Etymology (EN): Back formation from M.E. dosk, duske “dusky,” from O.E. dox “dark-haired, dark.”

Etymology (PE): Šâmgâh, from šâm “evening, evening meal”

• gâh “time.” The first component, šâm, from Mid.Pers. šâm “evening meal, supper,” from Av. xšāfnya- “evening meal,” from Av. xšap-, xšapā-, xšapan-, xšafn- “night” (O.Pers. xšap- “night;” Mid.Pers. šap; Mod.Pers. šab “night”); cf. Skt. ksap- “nigh, darkness;” Hitt. ispant- “night.” The second component gâh “time;” Mid.Pers. gâh, gâs “time;” O.Pers. gāθu-; Av. gātav-, gātu- “place, throne, spot;” cf. Skt. gâtu- “going, motion; free space for moving; place of abode;” PIE *gwem- “to go, come.”

Tiny pieces of solid material, such as carbon and silicate grains, in the → interstellar medium that are about 0.1-1.0 micron in size. → Dust grains embedded in → molecular clouds may be significantly larger.

Etymology (EN): O.E. dust, akin to O.H.G. tunst “storm,”
from P.Gmc. *dunstaz, from PIE base dhem-/dhemə- “to smoke, to blow,” cf. Skt. dhūmá “smoke,” Mod.Pers.
dam “smoke; to blow, breathe,” Av. dāδmainya- “blowing up,”
Gk. thumiao “to fumigate, burn incense,” thymos “spirit, mind, soul,”
L. fumus “smoke,” Ossetic dymyn/dumun “to smoke, blow up,” Lith. dumai “smoke.”

Etymology (PE): Qobâr, from Ar.; gard “dust,” Mid.Pers. gart, gard.

A chemical compound produced in laboratory experiments to simulate real
→ interstellar dust grains and thus study them.

See also: → dust; → analogue.

A process of formation of → dust grains in → interstellar medium and → protoplanetary disks, in which randomly colliding aggregates may stick together.

See also: → dust; → coagulation.

A small but vigorous → whirlwind, usually of short duration, rendered visible by → dust, → sand, and → debris picked up from the ground (Meteorology Glossary, Amer. Meteo. Soc.). See also → dust storm, → dust whirl.

See also: → dust; → devil.

Thermal emission in infrared from interstellar → dust grains
receiving photons. Dust grains absorb ultraviolet and visible light emitted by nearby stars and re-radiate in the infrared wavelengths. Since the infrared light is of lower energy than the ultraviolet/visible light, the difference goes into heating the dust grain. Typical temperatures for interstellar grains are tens of degrees Kelvin.

See also: → dust; → emission.

An emission or absorption mark in the spectrum of an astronomical object, the origin of which is attributed to the presence of dust in the object or on the line of sight.

See also: → dust; → feature.

A small, solid flake of → graphite and/or → silicates coated with water ice, found in the → interstellar medium
or the → interplanetary medium. Dust grains are irregularly shaped with sizes from microns to Angstroms (→ very small grain; → big grain; → PAH). It is believed that the dust is mainly formed in the cool outer layers of → red giants and dispersed in the interstellar medium.
In dense environments, such as
→ molecular clouds and around → protostars, dust grains grow due to collisions (→ grain growth). Therefore, dust grains in → protostellar disks should be larger than interstellar grains. Dust grains absorb and scatter optical and ultraviolet light and re-radiate in infrared (→ dust emission). Dust acts as a catalyst in the interstellar medium, because molecules form via reactions on the surface of dust grains.

See also: → dust; → grain.

A narrow, elongated structure of absorbing matter seen running over extended emission objects such as nebulae and galaxies.

Etymology (EN): → dust; lane, from O.E. lane, lanu “narrow hedged-in road,” cf. Du. laan “lane,” O.N. lön “row of houses,” of unknown origin.

Etymology (PE): Bâriké “a narrow thing,” from bârik “narrow,” from Mid.Pers. bārīk “narrow,” Av. bāra-, as in tiži.bāra- “sharp-edged,” from brāy- “to cut,” Mod.Pers. bor-, boridan “to cut;” qobâr→ dust.

A model of → dust grains conceived to describe the observed → interstellar extinction properties. It is characterized by the abundance of the different → chemical elements locked up in the dust, and by the → composition, → morphology, and → size distribution of its individual grains. For example, → MRN dust model.

See also: → dust; → model.

The → absorption of → electromagnetic radiation from an astrophysical object by → dust grains associated with that object.

Etymology (EN): → dust; → obscuration.

Etymology (PE): Tiregi, → obscuration, pat, → by; qobâr, → dust.

The scattering of → photons by → dust grains.

See also: → dust; → scattering.

A process occurring in → protoplanetary disks whereby relatively large → dust grains settle to the disk midplane.
These grains, with sizes from → micron to → millimeter, grow from smaller dust grains and will eventually give rise to a planetary system.

See also: → dust; → settling.

An unusual, frequently severe weather condition characterized by strong winds and dust-filled air over an extensive area. See also → dust devil, → dust whirl.

See also: → dust; → storm.

The tail of a → comet which is caused by → solar radiation pressure forcing the dust particles away from the → coma in a curved arch. Also called a → Type II tail.

See also: → dust; → tail.

An indication of the heat amount received by → dust grains
from the ambient → radiation field. Dust temperature depends on the optical properties and → sizes of grains (i.e., on the way they → absorb and → emit radiation) as well as on the → interstellar radiation field.
Most of the visible and → ultraviolet radiation in galaxies from stars passes through clouds of particles and heats them. This heating leads to re-radiation at much longer wavelengths extending to the millimeter.

See also: → dust; → temperature.

A rapidly rotating column of air (whirlwind) over a dry and dusty or shady area, carrying dust, leaves, and other light material picked up from the ground (Meteorology Glossary, Amer. Meteo. Soc.). See also → dust devil, → dust storm.

See also: → dust; → whirl.

A → stellar wind generated by the action of → radiation pressure on dust grains. This occurs in the case of cool stars, such as → AGB stars, with → effective temperatures below 2500 K when the density is sufficiently large. Since dust is a very good continuum absorber, the dust grains will be radiatively accelerated outward.

See also: → dust; → drive; → wind.

1. Something that one is expected or required to do by moral or legal → obligation.
   

2. The binding or obligatory force of something that is morally or legally right; moral or legal obligation.
   

3. An → action or → task required by a person’s position or occupation; → function (Dictionary.com).

Etymology (EN): M.E. du(e)te, from Anglo-Fr. duete, from O.Fr. deu “due, owed; proper, just,” from V.L. *debutus, from L. debitus, p.p. of debere “to owe.”

Etymology (PE): Harg, from Mid.Pers. harg, halg “duty, tribute; work, effort;” akin to Mod.Pers. gahulidan “to exchange, barter,” → exchange; cf. Wakhi (y)ark “work, matter, business”, Yaghnobi ark “work, matter, business,” Yighda hor, Munji hôr(g) “work;” Proto-Ir. *harH- “to pay tribute; to barter, trade, exchange;” cognate with Gk. elein “to take (by force),” elor “loot, looty, catch;” E. to sell (Cheung 2006).