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

A small circle on the celestial sphere whose plane is parallel to the celestial horizon. Same as → almucantar.

→ parallel; → altitude.

→ almucantar.

A solid figure whose six bases are → parallelograms, opposite pairs being identical and parallel.

From Gk. parallelepipedon, from parallelos, → parallel + epipedon "plane surface," from neuter of epipedos "flat," from → epi- + pedon "ground," cognate with L. ped-, pes, → foot.

Parâsuruyé, from parâsu, → parallel, + ruyé, → surface. Lowzivâr, from lowzi, → rhombus + -vâr, → -oid.

A four-sided → polygon whose opposite sides are parallel. A parallelogram all of whose angles are right angles is a → rectangle.

From Fr. parallélogramme, from L. parallelogrammum, from Gk. parallelogrammon "bounded by parallel lines," from parallelos, → parallel, + gramme "line," related to graphein "to write, draw" → -graph.

Parâsubar, from parâsu, → parallel, + bar, → side.

A paramagnetic substance, which possesses → paramagnetism.

→ para- + → magnet.

Relative to or characterized by → paramagnetism.

→ para- + → magnetic

The property of a substance that possesses a → magnetic permeability greater than that of a vacuum but significantly less than that exhibited by → ferromagnetism. In the absence of an external magnetic field the atomic → magnetic moments of the substance are randomly oriented and thus cancel each other out with no net total magnetic moment. Moreover the coupling between neighboring moments is weak. However, when a magnetic field is applied magnetic moments align with the direction of the field and so the magnetic moments add together. Therefore paramagnetic substances affect external fields in a positive way, by attraction to the field resulting in a local increase in the magnetic field. The → magnetization vanishes when the field is removed.

→ para- + → magnetism

General: Any of a set of physical properties whose values determine the characteristics or behavior of something. → impact parameter; → ionization parameter.
Math.: A constant or variable term in a function that determines the specific form of the function but not its general nature, as a in f(x) = kx, where k determines only the slope of the line described by f(x).

Mod.L. parametrum, from Gk. → para- + metron "measure," → meter.

Parâmun, from parâ-, → para-, + mun/mân "measure," as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl," from O.Pers./Av. mā(y)- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure."

Any of a set of equations that defines the coordinates of the dependent variables of a curve or surface in terms of one or more independent variables or parameters.

→ parametric; → equation.

An → ESO observatory, located on Cerro Paranal in the Atacama Desert, northern Chile, at 2,635 m altitude. It is about 120 km south of the town of Antofagasta and 12 km inland from the Pacific Coast. The Paranal Observatory hosts the → Very Large Telescope (VLT) with four 8.2 m telescopes. Each telescope provides one → Cassegrain and two → Nasmyth focus stations for facility instruments. One Nasmyth focus is available for visitor instruments. In addition each telescope is equipped with a → coudé focus station from which the light can be coherently combined in the interferometric focus. ESO also operates four 1.8 m Auxiliary Telescopes (ATs), that are used as an interferometric array (VISA) and a 4 m infrared survey telescope (VISTA). Currently, more than 10 instruments including two interferometric instruments (MIDI, AMBER) are operational and offered for science observations.

Paranal, the name of the mountain, in the Quechua language meaning "whirlwind;" → observatory.

An astronomical and meteorological calendar written by ancient Greeks from 450 B.C. during at least three centuries. The parapegma was an inscribed stone for public use. It had holes beside the inscription, in which a peg could be inserted next to the appropriate day. The term was later applied to purely written forms of such calendars, or almanacs; plural form parapegmata.

From → para- "next to" + pegma "something that fastens something else together," from pegnyein "to stick."

Characteristic of optical analyses that are limited to infinitesimally small apertures. Also called first-order or Gaussian optics.

→ para-; → axial.

From par(â)-, → para-, + âseyi→ axial.

A ray that lies close to and almost parallel to the optical axis and behaves according to paraxial equations.

→ paraxial, → ray.

A catalog of stars in the → Orion Nebula created by P. P. Parenago in 1954 (Publ. Astr. Inst. Sternberg, Band 25, p. 393-437, Moskau).

Pavel Petrovich Parenago (1906-1960), a Soviet astronomer.

1) General: A father or a mother. A precursor, or → progenitor.
2) Physics: A → nuclide that upon → radioactive decay or → disintegration yields a specific nuclide (the → daughter). See also → parent cloud, → parent element, → parent galaxy, → parent molecule.

From O.Fr. parent, from L. parentem (nominative parens) "father or mother, ancestor," from parere "to bring forth, give birth to, produce," from PIE base *per- "to bring forth"

Permâr, literally "father-mother" (as in Sogd. māt-pitri "parent"), from Gilaki per, → father, + Gilaki mâr, → mother.

Usually of a newborn star, the molecular cloud in which the star has formed.

→ parent; → cloud.

A radioactive element that spontaneously decays into a new substance. The product of this decay is known as a "daughter" element.

→ parent; → element.

Of a high redshift supernova, the galaxy in which the event has occurred.

→ parent; → galaxy.

The molecule initially produced when a comet nucleus sublimates, soon changed to different daughter molecules because of solar radiation.

→ parent; → molecule.

An atmospheric optical phenomenon, seen as a bright spot sometimes appearing at either side of the → Sun, often on a luminous ring or → halo and at the same angular elevation as the Sun. Parhelia are caused by the → refraction and → reflection of → sunlight by → ice crystals suspended in the Earth's → atmosphere. Also called mock Sun or sundog.

From Gk. parhelion "a mock Sun," from → para- "beside" + helios "sun," → helio-.

Parâhur, from parâ-, → para-, + hur "sun," → helio-.

1) General: Equality, as in amount, status, or character; equivalence; correspondence; similarity; analogy. Opposite of disparity.
2) Physics: The principle of space-inversion invariance.
An operation that reverses the algebraic sign of the coordinate axes used to describe a system, i.e. (x, y, z) → (-x, -y, -z). The parity principle is important in quantum mechanics because the wave functions which represent particles can behave in different ways upon transformation of the coordinate system. The parity is 1 (or even) if the wave function of the system is unchanged by an inversion of the coordinate system; it is -1 (or odd) if the wave function is changed only in sign. Parity is conserved in strong interactions, but not in weak ones.
3) Math.: The attribute, of an integer, of being even or odd. Thus, it can be said that 8 and 12 have the same parity, whereas 5 and 16 have opposite parity.
See also: → charge-parity symmetry, → even parity, → parity conservation, → parity symmetry, → parity violation.

From M.Fr. parité, from L.L. paritas "equality," from L. adj. par "equal."

Hamâli, quality noun of hamâl, → pair (equivalent 2).