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

A huge, → high-velocity cloud of hydrogen gas that measures some 9,800 × 3,300 → light-years. It is located between 36,000 and 45,000 light-years away from Earth in the northern constellation of → Aquila. It has a mass of at least 10⁶ → solar masses. It is now moving toward the disk of the → Milky Way at 73 ± 26 km/s and is expected to hit the disk of our Galaxy in about 27 million years, at an angle of approximately 45° at a point in the → Perseus Arm, one of two major → spiral arms of the Galaxy.

Named after Gail Bieger, née Smith, who discovered the cloud in 1963, when she was an astronomy student at Leiden University in the Netherlands; → cloud.

A fog combined with smoke or other forms of atmospheric pollutants in an unhealthy or irritating mixture.

From sm(oke) + (f)og; → smoke; → fog.

Dudmeh, from dud, → smoke, + meh, → fog.

A mass of tiny particles in the air that rises up from something burning.

M.E., O.E. smoca, related to smeocan "give off smoke;" cf. M.Du. smooc, Du. smook, M.H.G. smouch, Ger. Schmauch; PIE base *smeug(h)- "smoke" (cf. Arm. mux "smoke," Gk. smukho "to burn in a smoldering fire," O.Ir. much, Welsh mwg "smoke").

Dud, from Mid.Pers. dût, dûd "smoke;" Av. dunman- "cloud," duuan- "to fly;" cf. Skt. dhvan- "to smoke;" Hittite tuhhae- "to prouce smoke;" PIE base *dheu- "to blow, reel; smoke, dark."

1) Of a curve, free from bumps or abrupt irregularities.
2) To modify a sequential set of numerical data by reducing the differences in magnitude between adjacent values.

O.E. smoð "free from roughness, not harsh," of unknown origin.

Hamvâr "level, equal, an even place or thing," from ham- "same, equally, even; together, with" (Mid.Pers. ham-, like L. com- and Gk. syn- with neither of which it is cognate. O.Pers./Av. ham-, Skt. sam-; also O.Pers./Av. hama- "one and the same," Skt. sama-, Gk. homos-; originally identical with PIE numeral *sam- "one," from *som-. The Av. ham- appears in various forms: han- (before gutturals, palatals, dentals) and also hem-, hen-) + -vâr similarity suffix.

1) A curve which is free from abrupt fluctuations.
2) A curve if it has tangents at all points and the angle of inclination of the tangent is a continuous function of the arc length.

→ smooth; → curve.

A numerical method for modeling → compressible hydrodynamic flows, which uses particles to simulate a continuous fluid flow. Because the system of hydrodynamical basic equations can be analytically solved only for few exceptional cases, the SPH method provides a numerical algorithm to solve systems of coupled → partial differential equations for continuous field quantities. The main advantage of the method is that it does not require a computational grid to calculate spatial → derivatives and that it is a Lagrangian method, which automatically focuses attention on fluid elements. The equations of motion and continuity are expressed in terms of ordinary differential equations where the body forces become classical forces between particles. This method was first independently developed by Lucy (1977, AJ 82, 1013) and Gingold & Monaghan (1977, MNRAS 181, 375).

Smoothed Particle Hydrodynamics, first used by Gingold & Monaghan (1977); → smooth; → particle; → hydrodynamics.

An average of 13 monthly → sunspot numbers, centered on the month of concern. The 1st and 13th months are given a weight of 0.5.

→ smooth; → sunspot; → number.

The mathematical process that makes a curve smooth.

Verbal noun of → smooth.

A low-pass filter designed to reduce the amplitude of a ripple while freely passing the direct current obtained from a rectifier or direct-current generator. Also known as smoothing filter.

→ smoothing; → circuit.

A general name for a member of the large group of terrestrial and fresh-water gastropod molluscs which have a coiled shell. → slug.

M.E. snail, snayl(e), O.E. snegel; cognate with M.H.G. snagel, dialectal Ger. Schnegel.

Râb, dialectal Gilaki and Tabari (also see Dehxodâ). Halazun, from Ar.

The relationship between angles of incidence and refraction for a wave incident on an interface between two media with different indices of refraction. The law states that the ratio of the sine of the → angle of incidence to the sine of the → angle of refraction is a constant: n₁/n₂ = sinθ₂/sinθ₁. See also → refractive index. Also known as Descartes' law or the law of refraction.

Named after Dutch mathematician Willebrord Snellius (1580-1626), one of the discoverers of the law; → law.

A precipitation in the form of → ice crystals that falls from clouds when the air temperature is below 0 °C. Snow occurs when → water vapor in the → atmosphere forms directly into ice and completely bypasses the liquid stage of → precipitation. Once an ice crystal has formed, it absorbs up even more water vapor and freezes due to the surrounding atmosphere. The ice crystal then falls down to earth's surface in the form of a → snow crystal, snow → pellet, or more commonly known as the → snowflake. In short, snow formation requires the following conditions: 1) → relative humidity ≥ 100%, 2) → temperature < 0 °C, 3) presence of → condensation nuclei, and 4) → supercooled droplets.

O.E. snaw "snow;" cf. O.S., O.H.G. sneo, O.Fris., M.L.G. sne, M.Du. snee, Du. sneeuw, Ger. Schnee, O.N. snjor, Goth. snaiws "snow;" PIE base *sneig^wh- "to snow, snow;" cf. Mid.Pers. snêx, snêxr "snow;" Av. snaēg- "to snow," snaēžaiti "snows;" Skt. snih- "wet;" Gk. nipha "snowflake," neiphei "snows;" L. nix (genitive nivis); O.Ir. snigid "snows;" Lith. sniegas; Rus. snieg'.

Barf "snow," dialectal vafr "snow," var, from Mid.Pers. vafr "snow;" Av. vafra- in jaiwi.vafra- "with deep snow."

An → ice crystal forming snow in a → cloud.

→ snow; → crystal.

In a → protoplanetary disk, the limit between the regions where water is gaseous and the region where it is cold enough for water to become ice. The core accretion theory predicts that → giant planets form just outside the snow line where they can accrete enough rock and ice to generate a core. Subsequently the core grows into a gas giant like → Jupiter or → Saturn via the → accretion of hydrogen and helium. The snow line location depends on the → luminosity of the central star. For solar system it is about 5 AU, the position of Jupiter. Also known as ice line.

→ snow; → line.

Marz, → frontier; yax, → ice.

A mass of snow packed into a ball or rolled together, as for throwing.

→ snow; → ball.

Any of several episodes in the history of the Earth where our planet was entirely covered by glacial ice from pole to pole. There are at least three such episodes. The first one, called the Huronian glaciation, extended from 2.4 billion years ago to 2.1 billion years (lasting about 300 million years). In the last billion years, the Earth has experienced two more global glaciations: the Sturtian glaciation, which began 720 million years ago and, following a brief interglacial episode, the Marinoan glaciation, which ended 635 million years ago. During such episodes the global mean temperature would be about -50°C because most of the Sun's radiation would be reflected back to space by the icy surface. The average equatorial temperature would be about -20°C, roughly similar to present Antarctica. Without the moderating effect of the oceans, temperature fluctuations associated with the day-night and seasonal cycles would be greatly enhanced. Because of its solid surface, the climate on a snowball earth would have much in common with present Mars (http://www.snowballearth.org).

The term snowball Earth was coined in 1989 by Joe Kirschvink, a biomagnetist and paleomagnetist at the Caifornia Institute of Technology in Pasadena, USA; → earth.

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").

An agglomeration of many → ice crystals that falls as a unit from a cloud. Snowflakes possess a six-fold symmetry that ultimately derives from the six-fold symmetry of the ice crystal lattice. Typical snowflakes fall at a rate of 1-2 m s^-1. The shape of snowflakes is influenced by the → temperature and → humidity of the atmosphere. Snowflakes form in the atmosphere when cold water droplets freeze onto dust particles. Depending on the temperature and humidity of the air where the snowflakes form, the resulting ice crystals will grow into a myriad of different shapes. Snowflakes formed in temperatures below -22 °C consist primarily of simple crystal plates and columns whereas snowflakes with extensive branching patterns are formed in warmer temperatures. Snowflakes are not frozen raindrops. Sometimes raindrops do freeze as they fall, but this is called → sleet. Sleet particles do not have any of the elaborate and symmetrical patterning found in snow crystals.

From → snow + flake, from M.E. akin to O.E. flac- in flacox "flying" (said of arrows), O.N. flakka "to wander," M.Du. vlac "flat, level," M.H.G. vlach, Ger. Flocke "flake."

Golic "snowflake" in dialectal Lori and Laki (originally *geli-ka), variants Laki gal "seed (of millet)," gella "grape berry," Torbat-Heydariyei gella "grape berry," golla "ball, reel," Kurd. kuli, kilole "snowflake," Malâyeri gulu "bead," Qâyeni golle "bead," Qasrâni gella, golla "bead," Tabari gəlilə "bead," Gilaki gudé "ball, bowl, tumour," literary Pers. golulé, goruk "ball;" cf. Skt. guda- "ball, mouthful, lump, tumour;" Pali gula- "ball;" Gk. gloutos "rump;" L. glomus "ball," globus "globe;" Ger. Kugel; E. clot; PIE base *gel- "to make into a ball;" barf, → snow; dâné, → grain.

A piece of equipment mounted on the front of a vehicle for clearing away snow from roads, railroad tracks, etc.

→ snow + plow, → Plough.

Barfrub, from barf, → snow, + rub, rubidan "to sweep," → scan.

The third phase in the evolution of a → supernova remnant (SNR) occurring after the → Sedov-Taylor phase when the mass of the swept-up material becomes much larger than the amount of the ejected material. The SNR is surrounded by a cool → shell of accumulated material that is being pushed from behind, similar to what occurs for a snowplow. During this phase, → radiative cooling becomes important and the total energy is no longer conserved. Also called the → radiative phase.

→ snowplow; → phase.