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

The surface area of a black hole's horizon can never decrease.

→ second; → law; → black hole; → mechanics.

1) Heat cannot be transferred from a colder to a hotter body without some other effect, i.e. without → work being done. Expressed in terms of → entropy: the entropy of an → isolated system tends toward a maximum and its available energy tends toward a minimum.
2) In language of → statistical physics, an isolated physical system will tend toward an equilibrium → macrostate with as large a total → entropy as possible, because then the number of → microstates is the largest. See also → Kelvin's postulate, → Clausius's postulate.

→ second; → law; → thermodynamics.

In quantum mechanics, the quantization of the field that replaces potential in Newtonian mechanics, whereby the field variables become operators from which the creation (of particle) operators and destruction operators can be constructed.

→ second; → quantization.

An n extension of → first-order logic that quantifies not only → variables that range over → individuals, but also quantifies over → relations.

→ second; → order; → predicate; → logic.

1) Derived or derivative; not primary or original.
2) Belonging or pertaining to a second order, division, stage, period, rank, grade, etc.
3) → secondary body.
See also:
→ secondary atmosphere, → secondary calibrator, → secondary cell, → secondary cosmic rays, → secondary crater, → secondary eclipse, → secondary electrons, → secondary emission, → secondary mirror, → secondary star.

From → second + -ary a suffix occurring on adjectives (elementary; honorary; stationary) and nouns denoting objects, especially receptacles or places (library; rosary; glossary).

Dovomân, from dovom, → second.

An atmosphere of a planet that forms after primordial gases had been lost or had failed to accumulate. A secondary atmosphere develops from internal volcanic outgassing, or by accumulation of material from comet impacts. It is characteristic of terrestrial planets, such as Earth, Mercury, Venus, and Mars. → primordial atmosphere.

→ secondary; → atmosphere.

A body that revolves around a more massive body under the → gravitational attraction of the latter is called the → primary body.
The less massive component in a → binary system.

→ secondary; → body.

An indicator of extragalactic distances that relies on → primary calibrators in our Galaxy. Secondary calibrators of the distance scale depend on statistical measures of the properties of a class of objects, such as the brightness of H II regions, globular clusters, red and blue stars, or the neutral hydrogen 21-cm line width or velocity dispersion (of spiral galaxies), etc. Same as secondary distance indicator.

→ secondary; → calibrator.

An electric cell that can be charged by passing a current through it in reverse direction to its discharge. Same as → accumulator. See also → primary cell.

→ secondary; → cell.

A burst of secondary charged and neutral particles arising when → primary cosmic rays collide with the atmospheric oxygen or nitrogen nuclei in the upper atmosphere. The collision produces mostly → pions (π), along with some → kaons (K), → antiprotons, and → antineutrons. Neutral pions very quickly decay, usually into two → gamma rays. Charged pions also decay but after a longer time. Therefore, some of the pions may collide with yet another nucleus of the air before decaying, which would be into a → muon and a → neutrino. The fragments of the incoming nucleus also interact again, also producing new particles.

→ secondary; → cosmic; → ray.

A crater formed by the relatively low-velocity impact of fragments ejected from a large primary crater. Secondary craters tend to cluster in a ring around the primary crater.

→ secondary; → crater.

Of a transiting → exoplanet, the event and the interval of time during which the planet passes behind its host star. → primary eclipse.

→ secondary; → eclipse.

Electrons ejected from the atoms of a material when bombarded with high energy electrons. Secondary electrons are produced when an incident electron excites an electron in the material and loses some of its energy in the process. The excited electron moves toward the surface of the sample undergoing elastic and inelastic collisions until it reaches the surface, where it can escape if it still has sufficient energy. The secondary electron yield depends on many factors, and is generally higher for high atomic number targets, and at higher angles of incidence.

→ secondary; → electron.

The emission of → secondary electrons from the surface of a material when an incident particle (often, charged particle such as electron or ion) impacts the material with sufficient energy.

→ secondary; → emission.

The second reflecting surface in a → reflecting telescope. It directs the light either out a side opening of the tube (→ Newtonian telescope) or back toward a → focal point behind and through the → primary mirror (→ Cassegrain telescope). The secondary is usually suspended in the beam and therefore obstructs part of the primary.

→ secondary; → mirror.

A fainter rainbow appearing about 10° above the → primary rainbow, as viewed by the observer. The secondary rainbow is about twice as wide, and has its colors reversed.

→ secondary; → rainbow.

In a → binary system, the star that revolves around the more massive → primary component.

→ secondary; → star.

A part that is cut off or separated.
A distinct part or subdivision of anything. → cross section; → intersection

From M.Fr. section, from L. sectionem "a cutting, division," from secare "to cut;" PIE base *sek- "cut" (cf. O.C.S. seko, sesti "to cut," Lith. isekti "to engrave, carve;" O.S. segasna, O.E. sigðe "scythe;" O.E. secg "sword," seax "knife, short sword").

Sekanj "a scraping, shaving, cutting," cognate with Pers. šekast-, šekastan "to break;" Av. skand- "to break," Skt. khand- "to break," khanda- "piece;" Pers. dialect Tabari šag "a special razor used to make incisions in the walls of unripe opium poppies in order to extract the milky sap," may be related to PIE *sek- "cut," as above.

The smallest component of the aberration of starlight which is caused by the motion of the solar system through space. → annual aberration; → diurnal aberration.

→ secular; → aberration.

The apparent gradual increase in the → Moon's motion in its orbit, as measured relative to → mean solar time. Secular acceleration corresponds to an extremely gradual reduction in the speed of the → Earth's rotation. The slow-down of the Earth's spin comes mainly from → tidal frictions from the Moon. Historically, Edmond Halley (1656-1742) was the first to suggest that the Moon's mean rate of motion relative to the stars was gradually increasing. In 1693, Halley compared eclipses of recent, medieval, and classical Babylonian time, and discovered that the Moon's mean motion had been gradually increasing. Using Lunar Laser Ranging measurement, based on laser reflectors left by the Apollo astronauts on the Moon's surface (1969 to 1972), the secular acceleration is derived to be -25".4 ± 0".1 century ² (Xu Huaguan et al., 1996, in Earth, Moon and Planets 73, 101). This corresponds to a linear increase of about 3.5 cm yr^-1 in the mean Earth-Moon distance.

→ secular; → acceleration.