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

A certain place whose characteristics, as to location, altitude, atmospheric conditions, etc., make it appropriate for astronomical observations.

→ astronomical; → site.

One of a set of tables giving parameters used for calculations of positions of the Sun, the Moon, and the planets in particular in pre-telescopic astronomy. The oldest known astronomical tables are those of Ptolemy. In Modern astronomy it is usually replaced by the term → ephemeris. Same as → zij. See also → Toledan Tables, → Alfonsine Tables.

→ astronomical; → table.

One of the twilight phases when the Sun's center lies between 12 and 18 degrees below the horizon. Astronomical twilight is followed or preceded by → nautical twilight. Most stars and other celestial objects can be seen during this phase. However, some of the fainter stars and galaxies may not be observable as long as the Sun is less than 18 degrees below the horizon. See also → civil twilight.

→ astronomical; → twilight.

1) A unit of length equal to 149 597 870 700 m exactly, with symbol "au" (re-definition at the International Astronomical Union's 28th General Assembly in Beijing, China, August 20-31). The astronomical unit equals 1.5813 × 10^-5 → light-years and 4.8481 ×10^-6 → parsecs.
2) Previous definition: The radius of a circular orbit in which a body of negligible mass, and free of perturbations, would revolve around the Sun in 2 π / k days, where k is the → Gaussian gravitational constant. This is slightly less than the semi-major axis of the Earth's orbit.

→ astronomical; → unit.

The science of the celestial bodies and the Universe, dealing especially with the positions, dimensions, distribution, motion, chemical composition, energy, and evolution of celestial bodies and phenomena.

O.Fr. astronomie, from L. astronomia, from Gk. astronomia, from → astro- "star" + nomos "arranging, regulating," related to nemein "to deal out."

Axtaršenâsi, from axtar "star," → astro- + -šenâsi "knowledge" from šenâxtan "to know, to discern."

The area of science which deals with → elementary particle and → high-energy phenomena in → astrophysics and → cosmology.

→ astro-; → particle; → physics.

The photography of stars, other celestial bodies, and stellar fields.

→ astro-, → photography.

The measurement of the intensity of light of celestial bodies.

Astrophotometry, from → astro- + → photometry.

Axtar-šidsanji, from axtar-, → astro-, + -šidsanji, → photometry.

Of or pertaining to → astrophysics.

→ astrophysics + → -al

A very fast moving, → collimated beam of → ionized gas at high temperatures associated with most classes of compact objects that spin and/or accrete matter from their surroundings, such as → protostars, → X-ray binary systems, and, at a larger scale, with → active galactic nuclei, → gamma-ray bursts, and → quasars. In general, jet sources host → accretion disks and are associated with → magnetic fields. Astrophysical jets, despite their different physical scales and power, are morphologically very similar, suggesting a common physical origin. For example, in one extreme, → active galactic nuclei jets have typical sizes ≥ 10⁶ pc, velocities near that of light c, and parent sources (→ massive black holes) with masses 10^6-9  Msun and luminosities ~ 10^43-48Lsun; while in the other extreme, → young stellar objects jets have typical sizes ≤ 1 pc, velocities ≤ 10^-3 c, and emerge from low mass protostars with masses ~ 1 Msun and luminosities (0.1-2 × 10⁴) Lsun. Jets play an important → feedback role in the evolution of their host systems. See also: → jet launching.

→ astrophysical; → jet.

An extraterrestrial → object whose physical properties and formation are studied in → astrophysics.

→ astrophysical; → object.

A scientist who studies → astrophysics.

→ astro-; → physicist. The term astrophysicist was introduced by Greenwich astronomer Edwin Dunkin in 1869.

The branch of → astronomy that deals with the → physics of → celestial objects and the → Universe in general. It relies on the assumption that the → laws of physics apply everywhere in the Universe and throughout all time. See also → observational astrophysics, → theoretical astrophysics.

Astrophysics, from → astro- "star" + → physics. The first use of the term astrophysics has been attributed to Johann Karl Friedrich Zöllner (1834-1882) in 1865. He defined it as a coalescence of physics and chemistry with astronomy (History of Astronomy: An Encyclopedia, ed. John Lankford, Routledge, 1997).

Not having → symmetry.

→ asymmetry.

Lack of symmetry; not symmetrical.

Gk. asymmetria "lack of proportion," from asymmetros "ill-proportioned," from → a- "not" + symmetros "commensurable, symmetrical."

Nâhamâmuni, from nâ- "not" + hamâmuni "symmetry," from ham- "together = syn" + -â-, euphonic affix, + mun "measure" + -i, noun affix.

A straight line which is approached, but never reached, by an infinite branch of a curve, and which can be regarded as a line tangent to the curve at infinity.

Gk. asymptotos "not falling together," from → a- "not" + → syn "with" + ptotos "fallen," verbal adj. from piptein "to fall".

Nâhamsâv, literally "not touching each other," from nâ- "not" + ham "with" (akin to Gk. syn-) + sâv, agent noun of sâvidan "to touch."

Of or pertaining to an → asymptote.

Adjective from → asymptote; → -ic.

The phenomenon wherein the → quarks within a → hadron get closer together, the force of containment gets weaker so that it asymptotically approaches zero for close confinement. According to → quantum chromodynamics, the quarks in close confinement are completely free to move about. On the contrary, the further we try to force the quarks apart, the greater the force of containment. The 2004 Nobel Prize in Physics was awarded to David Gross, Frank Wilczek, and David Politzer for their discovery of asymptotic freedom. This discovery established quantum chromodynamics as the correct theory of the → strong interaction.

→ asymptotic; → freedom.

A region of the → Hertzsprung-Russell diagram populated by evolving → low-mass to → intermediate-mass stars. These stars have an electron → degenerate core of carbon and oxygen surrounded by two burning shells of helium and hydrogen. The H and He-burning shells are activated alternately in the deep layers of the star. An extended and tenuous convection envelope, having a radius of 10⁴-10⁵ times the size of the core, lies above these shells. The loosely bound envelope is gradually eroded by the strong → stellar wind, which forms a dusty → circumstellar envelope out to several hundreds of stellar radii. The convective envelope, stellar atmosphere, and circumstellar envelope have a rich and changing chemical composition provided by → nucleosynthesis processes in the burning shells in the deep interior.

→ symptotic; → giant; → branch.

For → stellar winds, same as → terminal velocity.

→ asymptotic; → velocity.