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

A radioactive dating technique, applied to organic materials, which measures the content of the radioactive isotope of carbon ¹⁴C. The radioactive carbon isotopes created by the impact of cosmic rays with the nitrogen atoms of the atmosphere find their way, via carbon dioxide and photosynthesis, into living material. When an organic material dies it ceases to acquire further ¹⁴C atoms, and its ¹⁴C fraction declines at a fixed exponential rate due to the radioactive decay of ¹⁴C. Comparing the remaining ¹⁴C fraction of a sample to that expected from atmospheric ¹⁴C allows the age of the sample to be estimated.

→ radiocarbon; → dating.

An element, such as uranium, whose isotopes are all radioactive.

→ radio; → element.

The process of producing an image on a sensitive surface by radiation such as X-rays or gamma rays passing through an object.

→ radio + → -graphy.

A synonym for radionuclide.

→ radio; → isotope.

The study and use of radiation and radioactive substances for the treatment of diseases.

→ radio; + → -logy.

The dissociation of molecules by radiation, for example in a reactor core, when the water used for cooling breaks down into hydrogen and oxygen.

From → radio + -lysis a combining form denoting "breaking down, loosening, decomposition," → analysis.

An instrument that measures the intensity of radiant energy.

→ radio; → -meter.

A dating method that uses measurements of certain radioactive isotopes to calculate the ages in years (absolute age) of rocks and minerals.

→ radiometer; → dating.

The detection and measurement of radiant energy, either as separate wavelengths or integrated over a broad wavelength band, and the interaction of radiation with matter in such ways as absorption, reflection, and emission.

→ radio + → -metry.

Tâbeš-sanji, from tâbeš, →radiation, + -sanj→ -metry.

A radioactive → nuclide.

→ radio + → nuclide.

A meteorological instrument that is carried aloft by a balloon to measure and send back information on atmospheric temperature, pressure, and humidity via radio to a ground receiving system.

→ radio + sonde, from Fr. sonde "sounding line."

→ radio; gomâné "a probe, a shaft sunk in order to ascertain the depth of the water when making a subterraneous canal," from Proto-Iranian *vi-mā-, from vi- "apart, away from, out" (cf. Av. vi-; O.Pers. viy- "apart, away;" Skt. vi- "apart, asunder, away, out;" L. vitare "to avoid, turn aside") + mā- "to measure" (cf. O.Pers./Av. mā(y)- "to measure;" Mod.Pers. mâ/mun/mân "measure," as in Pers. terms âzmâ- "to test;" pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl;" PIE base *me- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum).

A radioactive metallic chemical element; symbol Ra. Atomic number 88; atomic weight 226.0254; melting point 700°C; boiling point 1,140°C. Discovered in 1898 by Marie Sklodowska Curie in an ore of pitchblende. In 1911 Curie and André Debierne successfully isolated radium by electrolysis.

N.L., from L. rad(ius)" ray, beam" → radius + -ium a noun suffix.

Of a circle, any straight line segment extending from the center to a point on the circumference.
Of a sphere, any straight line segment extending from the center to a point on the surface.
Of a regular polygon, the radius of the circle circumscribed about the polygon.

From L. radius "staff, spoke of a wheel, beam of light," of unknown origin.

Šo'â', loan from Ar.

Same as → Larmor radius.

→ radius; → gyration.

Math.: In a system of polar or spherical coordinates, a line joining a point to the origin.
Astro.: A line drawn from a central body to a satellite object in any position in its orbit.

→ radius; → vector.

The base of a number system; thus 2 is the radix of the binary system, 10 the radix of the decimal system, 12 the radix of the duodecimal system.

From L. radix "root;" akin to Gk. rhiza "root;" cf. O.N. rot "root," O.E. wyrt "plant, herb;" E. radish.

Pâyé "basis, foundation; step," from pâ "foot, step" (from Mid.Pers. pâd, pây; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-).

A gaseous radioactive chemical element; symbol Rn. Atomic number 86; mass number of most stable isotope 222; melting point about -71°C; boiling point -61.8°C. Radon was discovered in 1900 by the German chemist Friedrich Ernst Dorn and it was first isolated in 1910 by the Scottish chemist William Ramsay and the English chemist Robert Whytlaw-Gray. The longest half-life associated with this unstable element is 3.8 day.

The name indicates its origin from → radium. It had first been called radium emanation or just emanation (with chemical symbol Em) because it was a decay product of radium. Ramsay subsequently suggested the name "niton" (with chemical symbol Nt), which means "shining" in Latin. It was finally changed to radon in 1923.

A flat structure made up of a collection of logs or planks fastened together for floating or transportation on water.

M.E. rafte, rafter, from O.N. raptr "log."

Sal "raft," probably related to PIE base *sel-, *swel- "beam, board," cf. Gk. selma "beam;" O.E. syll "beam, large timber," O.N. svill "framework of a building," M.L.G. sull, O.H.G. swelli, Ger. Schwelle "sill," and also akin to Mid.Pers. sard "ladder," Pers. dialectal variants (Lârestâni) se, si "ladder," (Gilaki, Tâleqâni) sardi, (Qazvini) sorda, (Hamedâni) serda, (Kâšâni) sart, sârda, serde, and others all meaning "ladder."

Water that is condensed from the aqueous vapor in the atmosphere and falls to earth in drops greater than 0.5 mm in diameter.

M.E. rein; O.E. regn; cf. O.S. regan; O.N. regn; M.Du. reghen; Ger. Regen; maybe cognate with Pers. (Tabari) rag "thunder;" (Šahmirzâdi, Semnâni, Sorxe-yi) rak "thunder;" (Gilaki) râk "cloudburst;" L. rigare "to wet, moist;" PIE *reg- "rain, damp."

Bârân, from 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."

A precipitation consisting of rain and partially melted snow. It usually occurs when the temperature of the air layer near the ground is slightly above freezing. Called sleet in British English speaking countries, but not in the United States where the term has a different meaning in meteorology.

→ rain; → snow; → mix.

Šaliv, of dialectal origin, Kurd. šalêwa "rain and snow mixed," Aftari šelâp, Qasrâni šelâb with the same meaning, Tabari šalâb "strong cloudburst." The first element šal, šel, šor, šâr, âbšâr, šâridan "to flow." The second element iv, êw, âp, âb, → water.