An Etymological Dictionary of Astronomy and Astrophysics

A metallic chemical element; symbol Rb. Atomic number 37; atomic weight 85.4678; melting point 38.89°C; boiling point 686°C; specific gravity 1.53 at 20°C. It was discovered in the mineral lepidolite by the German chemist Robert Wilhelm Bunsen and the German physicist Gustav-Robert Kirchoff in 1861. Bunsen isolated rubidium in 1863.

See also: From L. rubidus “deep red,” because of the two “deep red lines” in its spectra.

Red form of corundum, Al₂O₃, which owes its color to traces of chromium. Used in laser as a gem stone.

Etymology (EN): M.E. rubi, from O.Fr. rubi, from M.L. rubinus lapis “red stone,” from L. rubeus “red,” related to ruber→ red.

Etymology (PE): Yâqut, yâkand related to Gk. hyakinthos “hyacinth,” probably ult. from a non-I.E. Mediterranean language.

A set of astronomical tables created in 1627 by Johannes Kepler (1571-1630) based on observations by Tycho Brahe (1546-1601). These tables allowed Kepler to derive the three laws of planetary motions bearing his name (→ Kelpler’s laws). These are the first tables in which → atmospheric refraction has been taken into account. They overruled the → Prutenic Tables.

See also: From the L. title Tabulae Rudolphinae, in memory of Rudolf II (1552-1612), king of Hungary and Bohemia, and Holy Roman Emperor; → table.

A method for finding the value of a → polynomial given by a real number and deriving its → roots. It consists essentially of factoring the polynomial in a nested form. Also known as → nested multiplication.

See also: Named after Paolo Ruffini (1765-1822) and William Horner (1786-1837), who independently elaborated the method; → method.

An → induction coil
which was a forerunner of today’s automobile ignition coil. It consists of two coils wound on a single → iron core, and uses an → alternating current produced by a break-wheel to induce a high-voltage current in the secondary coil.

See also: After Heinrich Daniel Ruhmkorff (1803-1877), a German-born instrument maker, who settled in Paris in 1819 for the rest of his life; → coil.

1. A law or regulation that governs behaviors, actions, or operations. → Arnett’s rule, → commutation rule, → Fleming’s rule, → Hund’s rule, → left-hand rule, → Maxwell’s rule, → right-hand rule, → rigorous selection rule, → selection rule, and → Trouton’s rule.
   

2. A strip of rigid material marked off in units used especially for measuring length.
   

3. In some → planispheric astrolabes, a bar which rotates across the front of the astrolabe and is used to locate positions on the → rete, and to relate them to the scale of hours marked on the → limb. Also called the → index.

Etymology (EN): M.E. riule, reule, from
O.Fr. riule, from L. regula “straight stick, bar, ruler,” related to regere “to rule, straighten, guide;” cognate with Pers. râst “right, straight,” razan “rule,” as below.

Etymology (PE): Razan from Av. razan “rule, order,” from rāz- “to direct, put in line, set,” rasman- “the lines or files of the army;” O.Pers. rāsta- “straight, true,” rās- “to be right, straight, true;” Mid.Pers. râst “true, straight, direct;” Soghdian rəšt “right,” rây-, râyênitan “to arrange;”
Mod.Pers. râst “right, true; just, upright, straight;” raj “line, row,” variants raž, rak, râk, rezg (Lori), radé, râdé “line, rule, row,”
rasté, râsté “row, a market with regular ranges of shops;” ris, risé “straight;” cf. Skt. raj- “to direct, stretch,” rjuyant- “walking straight;” Gk. orektos “stretched out;” L. regere “to lead straight, guide, rule,” p.p. rectus “right, straight;” PIE base *reg- “move in a straight line,” hence, “to direct, rule.”

Same as → significance testing and → test of significance.

See also: → rule; → decision.

Te method of finding the fourth term in a proportion when three terms are given.

See also: → rule; → three.

A → diffraction grating with
a series of grooves that have been ruled on a reflective surface with a diamond tool mounted on a ruling machine. Ruled gratings may have triangular or trapezoidal groove profiles, whereas → holographic gratings usually have sinusoidal groove profiles.

Etymology (EN): Ruled, → rule; → grating.

Etymology (PE): Turi, → grating; šiyârdâr “having grooves,” from šiyâr, → groove, + -dâr “having, possessor,” → property.

A surface, such as a cylinder or cone, that can be generated by moving a straight line.

Etymology (EN): Ruled, p.p. of rule; → surface.

Etymology (PE): Ruyé, → surface; xatt sâxté “built, formed by a line,” from xatt→ line; sâxté, p.p. of sâxtan “to build, make, fashion; to adapt, adjust, be fit” (from
Mid.Pers. sâxtan, sâz-, Manichean Parthian s’c’dn “to prepare, to form;” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach”).

The hind part of the body of an animal, as the hindquarters of a quadruped or sacral region of a bird (Dictionary.com).

Etymology (EN): M.E. rumpe, from Scandinavian; compare Dan., Norw. Swed. rumpe rumpa “tail;” cognate with Ger. Rumpf “body, trunk.”

Etymology (PE): Kapal, maybe from Ar. kafal.
Sorin, → buttock.

An interval or period during which something, as a machine, operates or continues operating. → observing run.

Etymology (EN): Run, noun from verb, from M.E. ronnen, alteration of rinnen, (from O.E. rinnan and O.N. rinna) and of rennen, from O.N. renna; akin to O.H.G. rinnan; Ger. rinnen “to flow, run;”
Skt. rinati “he causes to flow,” and probably to L. rivus “stream;” PIE base *rei- “to flow.”

Etymology (PE): Dâv “a move, a turn (at play),” dâv zadan (kardan) “to make a move (at game),” variant dow (e.g. dow bé dast-e kasi oftâdan), maybe related to dow “run,” from davidan, dav- “to run;” Mid.Pers. dawidan, daw- “to run;” cf. Skt. dhāv- “to walk, hurry, flow,” dhāvati “flows, runs;” Gk. thoos “fast, quick;” O.E. deaw; E. dew; PIE base *dheu- “to flow.”

A massive, young, and hot star that is moving quickly through space. Runaways are probably propelled through space from a binary star when its companion has exploded as a supernova, or ejected from a stellar cluster by the dynamical interactions in the system.

Etymology (EN): → run; away, from O.E. aweg, earlier on weg “on from this (that) place;” → star.

Etymology (PE): Setâré, → star; gorizân present participle of goriz-, gorixtan “to escape; to flee, run away;” Mid.Pers. virextan;
Proto-Iranian *vi-raik, from vi- “apart, asunder”

• *raik; Av. raek- “to leave, set free, let off;” Mid./Mod.Pers. reg/rig (in mordé-rig “inheritance”); Skt. ric- “to leave,” rinakti “gives up, evacuates;” Gk. leipein “to leave;” L. linquere “to leave;” from PIE *linkw-, from
  *leikw- “to leave behind” (cf. Goth. leihvan; O.E. lænan “to lend;” O.H.G. lihan “to borrow;” O.N. lan “loan”).

The water or other liquids that drains or flows from the land into streams and rivers, eventually into seas.

Etymology (EN): From → run + → off.

Etymology (PE): Ravânâb, literally “flowing water,” from ravân “flowing, running,” pr.p. of raftan “to go, walk; to flow” (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack” + âb, → water.

Breaking apart or bursting. → plastic, → plasticity.

Etymology (EN): From L. ruptura “the breaking (of an arm or leg), fracture,” from p.p. of rumpere “to break.”

Etymology (PE): Pâregi “rupture,” from pâré, → partial; gosast, → Big Rip.

In, relating to, or characteristic of the → countryside.

Etymology (EN): M.E., from O.Fr. rural, from L ruralis “of the countryside,” from rur-,rus “open land, country;” cf. O.E. rum “space” (extent or time); O.H.G., Gothic rum, Ger. Raum “space,” ultimately from PIE root *reue- “to open; space,” source also of Av. ravah- “space,” O.Irish roi, roe “plain field,” O.C.S. ravinu “level,” Russ. ravnina “a plain.”

Etymology (PE): Rustâyi, adj. of rustâ, → countryside.

A coupling scheme of → electron configuration, used mainly for the lighter atoms with → atomic number less than 30. In an atom when changes in energy states are produced by the action of two or more electrons, the value of the total angular momentum of these electrons results from the coupling between the total → orbital angular momenta of the electrons and the total → spin angular momenta of the electrons. In this scheme the orbital angular momenta and spin angular momenta of electrons are added separately to give the total angular momentum L = Σ_i l_i and the total electron spin angular momentum S = Σ_i s_i. These are then added to give J = L + S.
Also called → LS coupling. See also → jj coupling.

See also: After Henry Norris Russell (1877-1957) and Frederick Albert Saunders (1875-1963), American astronomers (1925, ApJ 61, 38); → coupling.

A uniqueness theorem involving the equations of state of stellar structure. → Vogt-Russell theorem.

See also: Named after the German astronomer Heinrich Vogt (1890-1968) and the American astronomer Henry Norris Russell (1877-1957); → theorem.

Hydrated oxide of iron, mainly Fe₂O₃H₂O, formed on the surface of iron when it is exposed to moisture and air.

Etymology (EN): O.E. rust, related to rudu “redness,” from P.Gmc. *rusta- (cf. O.H.G., Ger. rost, M.Du. ro(e)st), from PIE base *reudh- “red” (cf. Lith. rustas “brownish,” rudeti “to rust;” L. robigo, O.C.S. ruzda “rust”).

Etymology (PE): Zang “rust,” variants žang, zangâr, of unknown origin.

A hard, silver gray metal belonging to the → platinum group
of metals; symbol: Ru. It is found directly above osmium in Group 8 of the periodic table. → Atomic number 44, → atomic weight 101.07, → melting point about 2,310°C, → boiling point about 3,900°C, → specific gravity 12.41 at 20°C.

See also: From L. ruthenia “Russia,” because it was first found by the Russian chemist Gottfried Wilhelm Osann in 1828, despite not being recognized as an element. In 1844 the Russian chemist Karl Karlovich Klaus was able to isolate the ruthenium metal.

A simple model assuming that the positive charge of the atom is not distributed uniformly throughout the atom (unlike the → Thomson atom), but is concentrated in a minute center or nucleus, and the negative charge is distributed over a sphere of radius comparable with the atomic radius.

See also: After the British physicist and chesmist Ernest Rutherford (1871-1937), who put forward this model in 1911; Nobel Prize in Chemistry in 1908; → atom.

An artificially produced radioactive chemical element; symbol Rf. Atomic number 104; mass number of most stable isotope 261; melting point, boiling point, and specific gravity unknown. Rutherfordium was discovered in 1964 by a team of scientists at the Joint Institute for Nuclear Research at Dubna in Russia who named the element kurchatovium. The Russian scientists were unable to duplicate their results and therefore lost credit to a team of scientists at the University of California, Berkeley, who identified the element. The scientists in California were successful in isolating the element after irradiating ²⁴⁹Cf with ¹²C.

See also: Named after the British physicist and chemist Ernest Rutherford (1871-1937), → Rutherford atom.