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

The plot that gives the portion of a signal's power falling within given frequency bins. The most common way of generating a power spectrum is by using a discrete Fourier transform.

→ power; → spectrum.

For a → random variable X, any → distribution which has the form: P(X ≥ x) = (k/x)^α, where x is a value in the range defined for X, k > 0 is a parameter termed location parameter, and α > 0 is the → slope parameter.

→ power; → law; → distribution.

An → elliptical galaxy whose → surface brightness can be approximated by a single → power law at small radii (r ≤ 10-20''). More modern interpretations have emphasized that these profiles can be better understood as the inward continuation of the galaxy's overall → Sersic profile, usually modified by an additional, nuclear-scale stellar component (S. P. Rusli et al., 2013, AJ 146, 160).

→ power; → law; → galaxy.

The amount of electromagnetic energy flowing through unit area, perpendicular to the direction of energy propagation, per unit time, given by (c/2 π)[E x H]. → Poynting's theorem.

→ Poynting's theorem; → vector.

The space through which electromagnetic radiation passes is filled with electric and magnetic fields at right angles to each other and to the direction of propagation of the radiation. The rate of energy transfer is given by the Poynting vector.

In honor of John Henry Poynting (1852-1914), English physicist; → theorem.

A loss of → orbital angular momentum by tiny ring particles associated with their absorption and re-emission of → solar radiation. Also known as the → Poynting-Robertson effect (Ellis et al., 2007, Planetary Ring Systems, Springer).

→ Poynting-Robertson; → drag.

The effect of → solar radiation on a small (centimeter-sized) particle in → orbit around the Sun that causes it to lose velocity and fall gradually into the Sun. The particle → absorbs solar radiation and → radiates the energy → isotropically in its own frame. The particle thereby preferentially radiates (and loses → angular momentum) in the forward direction in the → inertial frame of the Sun (aberration effect). This leads to a decrease in the particle's angular momentum and causes it to spiral sunward. In contrast, the → Yarkovsky effect is anisotropic; the object may be accelerated or decelerated.

→ Poynting's theorem; Howard Percy Robertson (1903-1961), American physicist and mathematician; → effect.

That can be done or used or put into practice.

→ practice; → -able.

Concerned with practice, as opposed to → theory.

→ practice; → -al.

1a) To do habitually or regularly.
1b) To exercise or follow as a profession.
2a) Performance; the doing of something (contrasted with → theory). See also → praxis.
2b) Way of doing something that is common or habitual.
2c) Frequent or systematic repetition in doing something.

M.E. practisen, practizen; O.Fr. practiser "to practice," from M.L. practicare "to do, perform," from L.L. practicus "practical," from Gk. praktikos "practical."

1) Varzidan "to practice, perform; to accustom oneself to; to labor; to sow a field;" Mid.Pers. warz- "to work, do, practice;" Av. varəz- "to work, do, perform, exercise;" cf. Gk. ergon "work;" Arm. gorc "work;" Lith. verziu "tie, fasten, squeeze," vargas "need, distress;" Goth. waurkjan; O.E. wyrcan "work," wrecan "to drive, hunt, pursue;" E. work; PIE base *werg- "to work."
2) varzé, noun from present stem varz- + suffix -é.

Actively following a specified career or way of life.

→ practice; → -ing.

A professional man, especially in medicine and the law.

Alteration of practician, → practice (+ -ian) + -er, → -or.

Varzmand, from varz, → practice, + -mand, → -ist.

An → open cluster in the constellation → Cancer containing about 50 stars of 6th magnitude or fainter. It lies 577 light-years away. Also called NGC 2632, the Beehive Cluster, or the Manger.

From L. praesepe "crib," from which cattle or horses are fed, manger; the neighboring brighter stars Gamma and Delta Cancri (Asellus Borealis and Asellus Australis) were pictured as asses which fed from a manger.

Perâysepé, loan from L., as above.
Kandu "beehive; a large earthen vessel in which grain is kept;" cf. Skt. kunda- "a bowl-shaped vessel, basin; the lower abdomen."
Âxor "manger," prefixed xor "to eat" (semantically like E. manger, Fr. mangeoire, from L. manducare, mandere "to chew, eat"), from Mid.Pers. âxwarr; Av. avô-x^varəna- "drinking fountain; a water spring," from avô- "water" + x^varəna-, from x^var- "to consume, eat;" Mid.Pers. xvardan "to eat, enjoy (food);" Mod.Pers. xordan "to eat, drink, devour," Laki dialect hovârden "to eat;" Proto-Iranian *huar- "to consume, eat."

Concerned with practical results and values; treating things in a practical way.

M.Fr. pragmatique, from L. pragmaticus "skilled in business or law," from Gk. pragmatikos "versed in business," from pragma (genitive pragmatos) "civil business, deed, act," from prassein "to do, act, perform."

Varzâl-gerâ, literally "practice-inclined," from varzâl, → practical, + -gerâ "inclining toward, intending, making for," → -ist.

A branch of → semiotics dealing with the relation between language and the users, especially the constraints they encounter in using language in social interaction, and the corresponding effects on other users in the communication.

→ pragmatic; → -ics.

Philo.: The doctrine that the truth or value of a concept or assertion is determined by its practical effects upon human interests.

→ pragmatic; → -ism.

A dimensionless number representing the ratio of the fluid viscosity to the thermal conductivity of a substance; a low number indicates high convection.

Named after the German physicist Ludwig Prandtl (1875-1953); → number.

1) The practice and practical side of knowledge or skills, as opposed to the → theory.
2) Accepted practice or custom.

M.L. praxis "practice, action," from Gk. praxis "practice, action, doing," from stem of prassein "to do, to act."

Varzidâr, from varzid past stem of varzidan, → practice, + -âr prefix forming nouns of action, such as kerdâr, raftâr, didâr, goftâr, jostâr, etc.

A precursor of a small, loosely bound → star cluster (→ bound cluster) as well as an → OB association, with masses ranging from about 10 to 1000 → solar masses or more.

→ pre-; → cluster; → core.

Same as → PG 1159 star.

→ post-; → degenerate; → star.