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

General: The fact of optimizing. The condition of being optimized. → optimize.
Computer science: Improving a system to reduce runtime, bandwidth, memory requirements, or other property of a system.

Verbal noun of → optimize

1) The power or right of choosing.
2) Something that may be or is chosen; choice.
3) The act of choosing (Dictionary.com).

→ opt; → -tion.

Left to one's choice; not required or mandatory (Dictionary.com).

→ option; → -al.

An electron contained within an atom which may be thought of as orbiting around the nucleus, in a manner analogous to the orbit of a planet around the Sun.

→ orbital; → electron .

An → orbital element that defines the angle between the orbital plane of a solar system body (planet, comet, asteroid) and the plane of the ecliptic. The orbital inclination of the Earth's orbit is 0°; those of Mercury, Venus, and Mars are 7.01°, 3.39°, and 1.85° respectively.

→ orbital; → inclination .

Theoretical prediction according to which a → giant planet, formed in the outer regions of a → protoplanetary disk, could migrate inward by losing → energy and → angular momentum as the result of → gravitational interactions with the remnants of the disk. This orbital migration could explain the presence of giant gaseous Jupiter-like planets (→ hot Jupiters) very close to their host stars.

→ orbital; → migration.

Same as → relativistic precession.

→ orbital; → precession.

The situation in which two orbiting objects exert a regular, periodic gravitational influence on each other and therefore their orbital frequencies are related by a ratio of two small → integers. Orbital resonance often results in an unstable interaction in which bodies exchange momentum and shift orbits until the resonance disappears. The resonance increases the eccentricity until a body approaches a planet too closely and the body is slung away.

→ orbital; → resonance.

A → differential equation in which the unknown function depends on only one → independent variable, as contrasted with a → partial differential equation.

→ ordinary; → differential; → equation.

1) The act or process of organizing.
2) The state or manner of being organized.
3) A group of persons organized for some end or work.

M.E. organizacion, from M.L. organization-, from organizatus p.p. of organizare "organize" + -ate.

Sâzmân, from sâz present stem of sâxtan, sâzidan "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") + -mân verbal noun suffix used with present and past stems, as in zâymân, câymân; sâxtemân, goftemân.

Note 1: The suffix -mân occurs extensively in some dialects, in particular in Garkuye-yi where it replaces the infinitive suffix -idan: resâmon (= rasidan "to arrive"), kešâmon (= kešidan "to draw"), kartemon (= kardan "to do"), bartemon (= bordan "to carry, bear"), paxdemon (= poxtan "to cook"), esbârtemon (= sepordan "entrust, make over to"), bâfdemon (= bâftan "to weave"), ašnofdemon (= šenidan "to hear"), terakâmon (= tarakidan "to blast"), teknâmon (= tekândan "to shake").

Note 2: -mân may be related to Av. suffix -man, which forms a number of derivative action-nous: rasman- "column, rank," from raz- "to direct;" vaēsman- "dwelling," from vaes- "to be or keep ready as, to serve as;" nāman- "name;" asman- "stone, heaven."

1) The position in relation to a specific place or object.
2) The act or process of orienting; the state of being oriented.

Verbal noun of → orient.

The Hunter. A prominent constellation, one of the largest in the sky, located on the celestial equator around 5h 30m right ascension, 0° declination. This constellation is rich in bright stars and nebulae. The brightest star is Rigel (β Orionis), visual magnitude 0.2. The second brightest star is → Betelgeuse (α Orionis), magnitude between 0.2 and 1.0. A key feature of Orion's constellation is his Belt of three bright stars that form a nearly straight line across its central parts. It contains also the → Orion Nebula, the only region of massive star formation visible to the unaided eye.

In Gk. mythology, Orion was a giant hunter and the enemy of Artemis the huntress, who according to some tales was responsible for his death. Other stories, though, tell how he pursued the Pleiades and with them was turned into a constellation to chase them forever across the sky.

Šekârgar, "→ hunter."

A minor → spiral arm of the → Milky Way Galaxy close to which the → Sun is located. It is some 3,500 → light-years across and approximately 10,000 light-years in length. The solar system lies close to the inner rim of this spiral arm, about halfway along its length. Its name derives from the fact that the stars closest to the Sun which actually lie within the arm are in the constellation → Orion. Its other designations are → Local Arm, → Local Spur, → Orion Bridge, → Orion Spur, and → Orion-Cygnus Arm.

→ Orion; → arm.

A large OB stellar association centered on the → Orion Nebula. Lying some 1500 → light-years away, it is about 400 light-years across and contains the main stars of Orion, except → Betelgeuse.

→ Orion; → association.

A part of a → molecular cloud toward the → Orion Nebula viewed edge-on. It is the surface of interaction between the → H II region and its → associated molecular cloud. Same as the → Orion Bright Bar.

→ Orion; → bar.

Same as → Orion Arm.

→ Orion; → bridge.

A prominent emission ridge in the → Orion Nebula located approximately 2' southeast of the → Trapezium cluster. Various observations have suggested that it is an escarpment in the main → ionization front of the Nebula seen almost edge-on. The Orion Bar is one of the nearest and best-studied → photodissociation regions.

→ Orion; → bright; → bar.

A controversial proposition according to which a coincidence would exist between the mutual positions of the three stars of → Orion's Belt and those of the main Giza pyramids. More specifically, Khufu, Khafre, and Menkaure would be the monumental representation of → Alnitak, → Alnilam, and → Mintaka, respectively.

→ Orion; → correlation; → theory.

A giant cloud, or complex of clouds, of interstellar gas and dust associated with the Orion nebula (M42). It is about 1,500 light-years away and measures about 240 light-years across. Besides M42 and M43 it contains a number of famous objects, including Barnard's Loop, the Horsehead Nebula, and the reflection nebulae around M78. Within this cloud, stars have formed recently, and are still in the process of formation.

→ Orion; → molecular cloud.

The best known → ionized nebula and one of the nearest regions to the Sun in which stars are presently being formed. It is visible to the naked eye in the constellation → Orion south of → Orion's Belt as a fuzzy patch. It lies about 1,500 → light-years away and measures about 30 light-years across. The Orion Nebula is ionized and made visible by a small group of → O-type and → B-type stars known as the → Trapezium cluster. Other designations: M 42, NGC 1976. See also: → Orion molecular cloud; → Huygens Region ; → Orion association; → Orion Bar; → Orion Bright Bar.

→ Orion; → nebula.