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

The hard nonmetallic mineral or group of consolidated minerals either in mass or in a fragment of pebble or larger size. See also → rock.

O.E. stan; cf. O.N. steinn, Dan. steen, O.H.G., Ger. Stein; from PIE *stai- "stone," also "to thicken, stiffen" (cf. Skt. styayate "curdles, becomes hard;" Av. stay- "heap;" Gk. stear "fat, tallow," stia, stion "pebble").

Sang "stone, rock;" Mid.Pers. sang; O.Pers. aθanga-; Av. asenga- "stone;" PIE *aken-.

A prehistoric period during which the main material used to make tools and weapons was stone. The Stone Age is usually divided into three separate periods (Paleolithic Period, Mesolithic Period, and Neolithic Period) based on the degree of sophistication in the fashioning and use of tools. The Paleolithic time period is by far the longest, beginning some two million years ago and ending around 10,000 BC to coincide with the end of the last ice age (Pleistocene epoch).

→ stone; → age.

A meteorite composed largely of rock-forming (→ silicate) → minerals. Stony meteorites are the most abundant kind, about 95%, of all meteorites. They are divided into two groups: → chondrites and → achondrites.

→ stone; → meteorite.

Meteorites comprised of roughly equal amounts of → nickel/→ iron and → stone. They are divided into two groups: → pallasites and → mesosiderites. The stony-irons are thought to have formed at the core/mantle boundary of their parent bodies. The stony-irons account for less than 2% of all known meteorites. Also called → siderolite.

→ stony; → iron; → meteorite.

A → stellar wind accelerated by radiation pressure in the continuum from a star with a luminosity above the → Eddington limit.

→ super-; → Eddington limit; → wind.

In some stellar models, particularly for evolved → massive stars, such as → red supergiants, → Luminous Blue Variables, and → Wolf-Rayet stars, an outermost layer of the stellar envelope where the luminosity might exceed the → Eddington limit. This is due to the → opacity peak produced by the variation in the ionization level of hydrogen in the outer → convective envelope, beneath the surface, of very luminous stars. The opacity peak generates supra-Eddington layers and density inversion. The high opacity decreases the Eddington luminosity in these layers, possibly to fainter levels than the actual stellar luminosity. As a result, the → radiative acceleration exceeds the → gravitational acceleration leading to → mass loss enhancement (see, e.g., A. Maeder, Physics, Formation and Evolution of Rotating Stars, Springer, 2009).

→ supra-; → Eddington limit; → layer.

The science or art of assembling, shaping, or ornamenting materials in construction; the constructive arts in general. → plate tectonics

L.L. tectonicus, from Gk. tektonikos "pertaining to building," from tekton (genitive tektonos) "builder, carpenter," → technique.

Sâzânik, from sâzân pr.p. of sâz-, sâxtan "to build, make, fashion; to adapt, adjust, be fit" (Mid.Pers. sâxtan, sâz-, Manichean Parthian s'c'dn "to prepare, to form;" Av. sak- "to understand, to mark," sâcaya- (causative) "to teach") + -ik, → -ics.

A → metric unit of → mass, equal to 1000 → kilograms.

M.E. tunne unit of weight or capacity (cf. O.Fris. tunne, M.Du. tonne, O.H.G. tunna, Ger. tonne), also found in M.L. tunna and O.Fr. tonne, perhaps from a Celtic source.

A musical sound of definite pitch, consisting of several relatively simple constituents called partial tones, the lowest of which is called the fundamental tone and the others harmonics or overtones.

M.E., from O.Fr. ton, from L. tonus "a sound, tone, accent," literally "stretching," from Gk. tonos "vocal pitch, raising of voice," related to teinein "to stretch," cognate with Pers. tanidan "to spin, weave," → tension.

Ton, loan from Fr., as above.

The seventh and the largest of → Neptune's satellites. It has a diameter of 2,700 km and orbits its planet at a mean distance of 354,760 km every 5.877 days. Triton was discovered by William Lassell in 1846 scarcely a month after Neptune was discovered. Triton is colder than any other measured object in the solar system with a surface temperature of -235° C. It has an extremely thin atmosphere. Nitrogen ice particles might form thin clouds a few kilometers above the surface. The atmospheric pressure at Triton's surface is about 15 microbars, 0.000015 times the sea-level surface pressure on Earth. Triton is the only large satellite in the solar system to circle a planet in a → retrograde motion, that is in a direction opposite to the rotation of the planet.

In Gk. mythology, Triton is a god of the sea, the son of Poseidon (Neptune); usually portrayed as having the head and trunk of a man and the tail of a fish.

The ratio of the → molar heat of vaporization of any liquid to its → boiling point is a constant, about 88 joules per mole per Kelvin. The rule is equivalent to the statement that the → entropy of vaporization is constant. It is not always followed, especially by liquids such as water in which hydrogen bonding occurs between the molecules.

Named after Frederick Thomas Trouton (1863-1922), an Irish physicist; → rule.

An experiment first carried out in 1903 to reveal the absolute motion of the Earth with respect to the → ether. The experiment consists of detecting a torque on a charged parallel-plate → capacitor that was suspended so that its plates were vertical. Since the Earth moves around the Sun, the moving charges were expected to produce magnetic fields, and the resulting torque should tend to turn the capacitor bringing its plates parallel to its velocity. No such effect was observed, and the absence of the torque supports the theory of → special relativity.

Named after Frederick T. Trouton (1863-1922) and Henry R. Noble; → experiment.

The simultaneous emission of two photons whose sum of energies is equal to that of a single electron transition. The energy of each individual photon of the pair is not fixed, so that the spectrum of two-photon emission is continuous from the wavelength of that transition to infinity. In practice, there is a peak in wavelength distribution of the emitted photons. Two-photon emission is studied atomic physics with application in astrophysics, as it contributes to the continuum radiation from → planetary nebulae. It was recently observed in condensed matter and specifically in → semiconductors.

→ two; → photon; → emission.

A stellar catalog which is the world's principal database of astrometric → double star information. It is maintained by the United States Naval Observatory. The WDS Catalog contains positions (J2000), discoverer designations, epochs, position angles, separations, magnitudes, spectral types, proper motions, and, when available, Durchmusterung numbers and notes for the components of 142552 systems (as of Feb 27 2018).

Washington, referring to the location of the United States Naval Observatory in Northwest Washington, D.C; → double; → star; → catalog.

An device consisting of four → resistances in series, used to determine the value of an unknown electrical resistance when the other three resistances are known.

Named after Charles Wheatstone (1802-1875), British physicist, who extensively used the circuit (1843) but was not its inventor. Such an arrangement of four resistances was first used by Samuel Hunter Christie (1784-1865) in 1833; → bridge.

An optical device for producing and analyzing polarized light. It divides incoming unpolarized light into two orthogonal, linearly polarized beams. It consists of two prisms of either quartz or calcite cemented together.

After the English scientist William Hyde Wollaston (1766-1828); → prism.

A European Space Agency's satellite, launched on 10 December 1999 and designed for the observation of → X-rays emitted by astronomical objects. The satellite carries three very advanced X-ray telescopes. The three corresponding European Photon Imaging Cameras (EPIC) are sensitive over the energy range 0.2 keV to 12 keV. Other instruments on-board are two reflection grating spectrometers which are sensitive below about 2 keV, and a 30 cm diameter → Ritchey-Chretien optical/UV telescope. The telescope moves in a highly elliptical orbit, traveling out to nearly one third of the distance to the Moon and enabling long, uninterrupted observations of faint → X-ray sources. The original mission lifetime was two years, it has now been extended for further observations until at least 2010. Among recent results obtained using XMM-Newton one can mention an intermediate-mass black hole of over 500 solar masses in the galaxy ESO 243-49 (Nature 460, 73, 2009) and broad line emission from iron K- and L-shell transitions in the active galaxy 1H 0707-495 (Nature 459, 540, 2009). See also → X-ray astronomy.

XMM, from "X-ray Multi-Mirror;" Newton, in honor of Sir Isaac Newton, → newton.