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

Electricity: Any load which exceeds the rated output of a machine, transformer, or other apparatus.

→ over-; → load.

A silvery white metal which belongs to the → platinum group elements, symbol Pd. → Atomic weight 106.4, → atomic number 46, → melting point 1554.9 °C, → boiling point 2963 °C. It is used in alloys and as a catalyst.

Named 1803 by discoverer William Hyde Wollaston (1766-1828), after the asteroid → Pallas, which was discovered at about the same time.

1) General: A typical example of something.
2) Grammar: A set of word forms giving all of the possible inflections (declensions, conjugations) of a word.
3) Philosophy of science: A framework of concepts, results, and procedures within which subsequent work is carried out, as defined by the influential Thomas Kuhn (1922-1996) in his classic The Structure of Scientific Revolutions (1962). "Normal science" proceeds within such a framework or paradigm. When a paradigm has to be changed (→ paradigm shift), there comes about a crisis and then scientific revolution. For example, Newton's mechanical paradigm was replaced by the paradigm of Einstein's relativistic universe. Each paradigm is an interpretation of the world, rather than an objective explanation. For criticism of Kuhn's views, see, e.g., Stanford Encyclopedia of Philosophy.
4) Term now occurring frequently in every kind of discourse, usually to mean something like "way of thinking" or "approach to a problem."

L.L. paradigma "pattern, example," especially in grammar, from Gk. paradeigma "pattern, model," from paradeiknynai "to exhibit, show side by side," from → para- "beside" + deiknynai "to show," related to dokein "to appear, seem, think," cognate with Av. daēs- "to show" (Mod.Pers. andišé, andiš "thought, think," see below); Skt. diś- "to show, point out," diśati "he shows;" L. dicere "to utter;" PIE base *deik- "to show, to pronounce."

Parâdiš, pârâdiš, from parâ-, pârâ, → para- + diš "to show," as in andiš, andišidan "to → think" (related to dis, disé, → form); Sogd. andiš "to seem," andêš "to show," andêšik "appearing;" ultimately from Av. daēs- "to show," s-aorist forms dāiš-, dôiš-, diš-, akin to Gk. deiknynai "to show," as above, dike "manner, custom;" Skt. diś- "to show, point out;" L. dicere "to utter, say;" O.H.G. zeigon, Ger. zeigen "to show;" O.E. teon "to accuse," tæcan "to teach."

1) Philosophy of science: A process of revolutionary change in scientific → paradigms, whereby established scientific ideas are replaced by new ones. For instance, Copernicus' evidence that the Earth revolved around the Sun caused a paradigm shift in astronomy.
2) The idea of paradigm shift has been transferred from the sciences to other areas of society and culture, referring to a fundamental reorganization of how people think about an entire topic.

→ paradigm; → shift; → change.

A statement, proposition, or situation that seems self-contradictory or absurd but in reality is or may be true. → Fermi paradox; → faint early Sun paradox; → twins paradox; → paradox of youth.

From L. paradoxum "contrary to expectation," from Gk. paradoxon, from neuter of adj. paradoxos "contrary to common opinion, unbelievable," from → para- "contrary to" + dox(a) "opinion, belief" + -os adj. suffix. The main component dox, from dokein "to appear, seem, think," is cognate with Av. daēs- "to show;" Skt. diś- "to show, point out," diśati "he shows;" L. dicere "to utter;" PIE base *deik- "to show, pronounce solemnly."

Pârâdaxš (on the model of Gk. paradoxos), from pârâ-, → para-, + daxš, from Av. daxš- "to reveal, instruct, point out," fradaxštar- "teacher," *daxšārə "revelations;" Mod.Pers. daxš "task, effort;" cf. Skt. daks- "to be able," dáksa- "able, expert."

The observed presence of young stars in the immediate vicinity of the → supermassive black hole (SMBH), → Sgr A*, residing in the center of our Galaxy. The stellar population within 1 pc of the SMBH contains a variety of young and → massive stars orbiting the SMBH. Some of them are only about 20 Myr old and get as close as a few light-days to the SMBH, while from 0.1 to 0.4 pc even younger stars are found with ages of 3-7 Myr. The presence of these stars so near to the SMBH is a paradox. Their → in situ formation should be almost impossible, since the environment is too hostile for these stars to form. Indeed the strong → tidal influence of the SMBH should hamper their formation. On the other hand, the scenario considering their → migration from other places does not seem to be adequate. The time required for the migration from > 1 pc by dynamical friction would exceed their inferred ages unless the migration rate were somehow accelerated. This apparent contradiction was termed "paradox of youth" by Ghez et al. (2003, ApJ 586, L127). See also Genzel et al. (2010, Rev.Mod.Phys. 82, 3121, also at astro-ph/1006.0064).

Youth, the condition of being → young; → paradox.

→ advance of perihelion.

→ advance of perihelion.

A blue, → main sequence star of → apparent visual magnitude 2.44 and → spectral type A0 Ve located in → Ursa Major. Other designations: Phecda; Phekda; Phegda; Phekha; Phacd.

Phad, from Ar. al-Fakhidh (ad-Dubb) (الفخذ‌الدب) "the thigh (of the Bear)".

Faxez, from Ar., as above.

A blue → giant star in the constellation → Ursa Minor, also known as HR 5735, HD 137422, HIP 75097, BD+72°79, and SAO 8220. It has an → apparent visual magnitude of +3.0, → color indices of B -V = +0.09, U - B = +0.08, and a → spectral type of A2 III. Pherkad has a → luminosity of 1,100 Lsun, a radius of 15 Rsun, and a → surface temperature of 8,200 K. It lies 487 → light-years away from Earth.

From Ar. Al-Farqad (الفرقد) "calf."

Same as → physisorption.

→ physical; → adsorption.

An equation that expresses the energy radiated per unit area per unit time per unit wavelength range by a blackbody as a function of temperature. It is expressed by → Planck's blackbody formula.

→ Planck; → radiation; → law.

A prominent → open cluster in the constellation → Taurus, popularly called the Seven Sisters. It is a very young cluster of several hundred stars (with spectral types B6 and later), spanning over 1.5 degrees on the sky and about 400 → light-years distant. Six members of the cluster are visible to the → naked eye, the brightest one being → Alcyone. The cluster contains extensive nebulosity, consisting of dust clouds that reflect the light of the → embedded stars. Other designations: M45, NGC 1432.

In Gk. mythology, the seven daughters of Atlas and Pleione, transformed by Zeus into seven stars, from L., from Gk. Pleiades, perhaps literally "constellation of the doves," from a shortened form of peleiades, plural of peleias "dove," from PIE base *pel- "dark-colored, gray."

Parvin, variants Parv, Parvé, Paran, Parand, Parviz, Kurd. Pêrû, Pashtu Pêrûne, Baluchi Panvar; Mid.Pers. Parwiz. According to Bartholomae, it originates from Av. Paoiryaēini-, the first component paoirya- denoting "first." Alternatively, the first element in Parvin may be related to Av. parav-, pauru-, pouru- "full, much, many" (Mod.Pers. por "full, much, very;" Mid.Pers. purr "full;" O.Pers. paru- "much, many," from par- "to fill;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full), denoting "many, numerous," because the object contains several stars.

The two-dimensional intensity distribution about the image of a point source.

→ point; → spread; → function.

At a point, the rate of change of potential V, with distance x, measured in the direction in which the variation is a maximum. The intensity F of the field is proportional to the potential gradient, but is oppositely directed: F = -dV/dx.

→ potential; → gradient.

A broadening of spectral lines caused mainly by the stellar atmospheric density and the surface gravity of the star. The line strength of a spectral line depends on the number of atoms in the star's atmosphere capable of absorbing the wavelength in question. For a given temperature, the more atoms there are, the stronger and broader the spectral line appears. Denser stars with higher surface gravity will exhibit greater pressure broadening of spectral lines.

→ pressure; → broadening.

The pressure difference between two adjacent regions of a fluid that results in a force being exerted from the high pressure region toward the low pressure region.

→ pressure; → gradient.

A force resulting from → pressure gradient that is directed from high to low pressure.

→ pressure; → gradient; → force.

The third principle of → formal logic introduced in Aristotle's theory of the → syllogism: No statement can be both → true and → false at the same time. Also called → law of non-contradiction.

→ principle; → non-; → contradiction.

A rotational or orbital movement that is the same as most bodies within a celestial system. In the solar system, the apparent eastward motion of a celestial body on the celestial sphere. Opposed to → retrograde motion. Same as → direct motion.

From → pro- "forward" + grade, from L. gradi "to go, step, walk;" → motion.

Jonbeš, → motion; farârow, from farâ- "forward," → pro-, + row present stem of raftan "to go, walk;" Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack."

Same as →prograde motion.

→ prograde motion; → orbit.