An Etymological Dictionary of Astronomy and Astrophysics

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

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

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

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

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

Etymology (PE): 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.

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

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.

See also: 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.

Etymology (EN): 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’.

Etymology (PE): Barf “snow,” dialectal vafr “snow,” var,
from Mid.Pers. vafr “snow;” Av. vafra- in jaiwi.vafra- “with deep snow.”

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.

Etymology (EN): 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’.

Etymology (PE): 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.

See also: → snow; → crystal.

An → ice crystal forming snow in a → cloud.

See also: → 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.

Etymology (EN): → snow; → line.

Etymology (PE): Marz, → frontier; yax, → ice.

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.

Etymology (EN): → snow; → line.

Etymology (PE): Marz, → frontier; yax, → ice.

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

See also: → snow; → ball.

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

See also: → 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).

Etymology (EN): 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.

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).

Etymology (EN): 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.

Etymology (EN): → snow; → drift.

Etymology (PE): 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”).

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

Etymology (EN): → snow; → drift.

Etymology (PE): 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.

Etymology (EN): 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.”

Etymology (PE): 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.

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.

Etymology (EN): 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.”

Etymology (PE): 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.

Etymology (EN): → snow + plow, → Plough.

Etymology (PE): Barfrub, from barf, → snow, + rub, rubidan “to sweep,” → scan.

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

Etymology (EN): → snow + plow, → Plough.

Etymology (PE): 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.

See also: → snowplow; → phase.

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.

See also: → snowplow; → phase.

A ring-like structure of swept-up → gas and → dust around a → supernova remnant. See also: → free expansion phase, → Sedov-Taylor phase, → snowplow phase.

See also: → supernova remnant (SNR); → shell.

A ring-like structure of swept-up → gas and → dust around a → supernova remnant. See also: → free expansion phase, → Sedov-Taylor phase, → snowplow phase.

See also: → supernova remnant (SNR); → shell.