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

An asteroid that could make a threatening close approach to the Earth. In technical terms a PHA is defined as having an → absolute magnitude of 22 or brighter and an → Earth Minimum Orbit Intersection Distance (MOID) of less than 0.05 → astronomical unit or 7.5 million km.

→ potentially; → hazardous; → asteroid.

The total liquid product of precipitation or condensation from the atmosphere, as received and measured in a rain gauge.

→ rain + → fall.

Bâreš verbal noun of bâridan "to rain," bâridan "to rain;" Mid.Pers. vârân "rain," vâritan "to rain;" Av. vār- "rain; to rain;" cf. Skt. vār- "rain, water; to rain;" L. urinari "to plunge under water, to dive;" Gk. ourein "to urinate;" PIE base *uer- "water, rain, river."

In reality; actually; indeed.

→ real; → -ly.

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

→ rift; → valley.

The angle subtended at a star by a baseline that is the distance the Sun moves in a given interval of time with respect to the local standard of rest (4.09 AU per year).

→ secular; → parallax.

Of little depth; not deep.

M.E. schalowe, akin to O.E. sceald "shallow."

Nažal, from negation prefix na-, → non-, + žal "deep," variant of jal, jol, jul, → deep.

Low angle, → grazing incidence.

→ shallow; → angle.

Of limited size; of comparatively restricted dimensions; not large. → method of small perturbations; → Small Magellanic Cloud (SMC).

M.E. smale; O.E. smæl "slender, narrow, small;" cf. Dan., Swed., M.Du., Du., O.H.G. smal, O.Fris. smel, Ger. schmal "narrow," Goth. smalista "smallest."

Kucak "small;" Mid.Pers. kucak "small," related to kutâh "short, small, little," kudak "child, infant," kutulé, → dwarf; Mid.Pers. kôtâh "low," kôtak "small, young; baby;" Av. kutaka- "little, small."
Kam "little, few; deficient, wanting; scarce," from Mid.Pers. kam "little, small, few," O.Pers./Av. kamna- "small, few."

Same as → Little Dipper.

→ small; → Little Dipper.

An irregular galaxy, the smaller of the two → Magellanic Clouds that are satellites of our own Galaxy, lying in the southern constellation → Tucana about 20 degrees from the → south celestial pole. The SMC covers an area roughly 3 by 5 degrees in dimension and has an overall → visual magnitude about +2.7. The SMC is about 10,000 → light-years in diameter and some 210,000 light-years (61 → kpc) away. It has a visible mass of about 1/50-th that of our Galaxy and 1/10-th of that of the → Large Magellanic Cloud (LMC). Its → heavy element content is about a factor 5 smaller than that of the Galaxy. The SMC is the third-nearest external galaxy after the → Sagittarius Dwarf Elliptical Galaxy and the LMC.

→ small; → Magellanic; → cloud.

A term introduced by the → International Astronomical Union (August 2006) to name the → solar system bodies other than → planets and → dwarf planets. Small solar system bodies include → asteroids, → comets, and → meteoroids.

→ small; → solar; → system; → body.

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.

The proportion of the solar matter made up of → chemical elements heavier than → helium. It is denoted by Z, which represents the sum of all elements heavier than → helium, in mass fraction. The most recent determination of the solar Z gives a value of 0.0134 (Asplund et al. 2009, ARAA 47, 481), corresponding to the present-day photospheric composition.

→ solar; → metallicity.

The angle subtended (8''.79) by the → equatorial radius of the Earth at a distance of 1 → astronomical unit.

→ solar; → parallax.

A small, free balloon sent into the upper atmosphere to measure, record, and transmit meteorological reports to a ground station.

→ sounding; → balloon.

1) A chip or splinter.
2) To break up into small chips, flakes, or splinters, or to cause to break off in flakes.

M.E. spalle "a chip," verb spald "to split," from M.L.G. spalden, cognate with O.H.G. spaltan "to split."

Terišé "a chip," from tarâšidan "to cut, hew; scape; shave;" Mid.Pers. tâšitan "to cut, cleave; create by putting together different elements;" Av. taš- "to cut off, fashion, shape, create," taša- "axe" (Mod.Pers. taš, tišé "axe"), tašan- "creator;" cf. Skt. taks- "to form by cutting, tool, hammer, form," taksan- "wood-cutter, carpenter;" Gk. tekton "carpenter," tekhne "art, skill, craft, method, system;" L. textere "to weave;" PIE *teks- "to fashion."

A nuclear reaction in which a high energy particle that collides with a nucleus causes the target to eject several particles, thus changing both its mass number and its atomic number.

From → spall + -ation.

Verbal noun from terišidan, → spall.

The measurement of a stellar distance by the absolute magnitude derived from the luminosity criteria of the spectrum and the apparent magnitude of the star.

→ spectroscopic; → parallax.

A sudden, violent gust of wind, often accompanied by rain, snow, or sleet. A sudden increase of the mean wind speed which lasts for several minutes at least before the mean wind returns to near its previous value. It is often accompanied by rain or snow.

Probably from a Scand. source (cf. Norw. skval "sudden rush of water," Sw. skvala "to gush, pour down").

Bâdzad, from bâd, → wind + zad past stem of zadan "to strike, beat; to do; to play an instrument" (Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *g^when- "to strike, kill").