An Etymological Dictionary of Astronomy and Astrophysics

That can be done or used or put into practice.

See also: → practice; → -able.

Concerned with practice, as opposed to → theory.

See also: → 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.

Etymology (EN): 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.”

Etymology (PE): 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.

See also: → practice; → -ing.

A professional man, especially in medicine and the law.

Etymology (EN): Alteration of practician, → practice (+ -ian)

• -er, → -or.

Etymology (PE): 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.

Etymology (EN): 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.

Etymology (PE): 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.

Etymology (EN): 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.”

Etymology (PE): 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.

See also: → pragmatic; → -ics.

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

See also: → 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.

See also: 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.

Etymology (EN): M.L. praxis “practice, action,” from Gk. praxis “practice, action, doing,” from stem of prassein “to do, to act.”

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

A prefix meaning “before, prior to, in advance of, early, beforehand, in front of.”

Etymology (EN): M.E., from O.Fr. pré-, from L. præ (adverb) “before.”

Etymology (PE): Piš- “before; in front,” from Mid.Pers. pêš “before, earlier,” O.Pers. paišiya “before; in the presence of.”

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.

See also: → pre-; → cluster; → core.

Same as → PG 1159 star.

See also: → post-; → degenerate; → star.

A technique in spectroscopy which uses a combination of several dispersive elements (prisms in series or a grism) before focusing the light on the primary disperser, usually a grating, in order to achieve high spectral resolutions.

See also: → pre-; → dispersion.

A → Herbig AeBe star displaying → forbidden emission lines in its spectrum.

See also: → pre-; → main; → sequence; → B[e] star.

A → binary system whose components are → pre-main sequence stars.

See also: → pre-; → main sequence; → binary.

A star that evolves in the → Hayashi phase and has not yet reached the → zero-age main sequence.

See also: → pre-; → main sequence,
→ star.

The stage of a star before its eruption to become a nova.

See also: → pre-; → nova;
→ stage.

An adjective relating to a stage before the formation of a → protostar. → pre-stellar core.

See also: → pre-; → stellar.

A small, gravitationally unstable molecular → clump of typical size of less than 0.1 pc resulting from → gravitational collapse and → fragmentation of a larger → molecular cloud. It is a centrally concentrated structure which evolves into a → class 0 object, where eventually a single star or a stellar system is formed. Core masses range between 0.5 and 5 solar masses, with a mean number density of at least 10⁴-10⁵ cm^-3, and a temperature as low as about 10 K. A pre-stellar core evolves into a → Class 0 object. Also called dense core.

See also: → pre-stellar; → core.

A → post-planetary nebula star that is approaching the top of the → white dwarf sequence. These stars have exhausted the capacity of → nuclear burning in their cores.

See also: → pre-; → white; → dwarf.

Existing before or making possible the appearance of living organisms. Prebiotic molecules are biologically essential components
such as amino acids, sugars, and nucleic-acid bases which are precursors of the origin of life.

See also: → pre- + → bio- + -tic equivalent of → -ic.

1. To correct celestial coordinates for → precession.
   
2. To undergo → precession.

Etymology (EN): Back formation from → precession.

Etymology (PE): Back formation from pišâyân, → precession.

The apparent position of a celestial object corrected for the epoch → precession.

See also: Precessed, p.p. of → precess;
→ coordinates.

The periodic motion of the → rotation axis of a
body such as a → spinning top in which the axis of rotation gradually sweeps out a conical shape. In the case of the spinning Earth, it is due to the combined → gravitational attractions of the → Sun, the → Moon, and → planets on Earth’s → equatorial bulge. Since
the Earth’s axis is tilted to its → orbital plane or
→ ecliptic, the gravitational force of the Sun and the Moon on the Earth’s equatorial bulge tend to pull it back toward the plane of ecliptic. As a result, the axis → precesses. Earth’s axis of rotation precesses with a period of about 25,770 years, describing
one complete circle on the → celestial sphere
(→ precession constant). This circle has a radius of approximately 23°.5, equal to the → inclination of the Earth’s orbit. Since the → vernal equinox is the reference direction for the → equatorial coordinate system, the coordinates of “fixed” objects change with time and must therefore be referred to an → epoch at which they are correct.
→ sign of zodiac.

See also → general precession; → precession of the ecliptic; → precession of the equator; → precession of the equinoxes; → precessional circle; → precession time; → geodetic precession; → general precession in longitude; → general precession in right ascension; → orbital precession; → perihelion precession; → planetary precession; → precession period.

Etymology (EN): L.L. præcissionem “a coming before,” from L. præcessus, p.p. of præcedere “to happen before,” from the fact that the equinoxes occur earlier each year with respect to the preceding year,
from præ- “before,” → pre-, + cedere “to walk, to go, to happen.”

Etymology (PE): Pišâyân, literally “coming before,” from piš- “before” → pre- + ây- (present stem of âmadan “to come, arrive, become”), from Av. ay- “to go, to come,” aēiti “goes;” O.Pers. aitiy “goes;” Skt. e- “to come near,” eti “arrival;” L. ire “to go;” Goth. iddja “went,” Lith. eiti “to go;” Rus. idti “to go;”

• -ân suffix of space and time.

The amount by which the equinoctial points drift westward annually due to precession. Its value for epoch J2000.0 is 50’’.26, resulting from the westward → precession of the equator (50".38), and the eastward → precession of the ecliptic (0".12).

See also: → precession; → constant.

The component of general precession caused by the gravitational attraction of the planets on the Earth’s center of mass. It causes the equinox to move eastward by about 0’’.12 per year in the opposite direction to
the → precession of the equator. This terminology replaces → planetary precession, according to an IAU resolution adopted in August 2006.

See also: → precession; → ecliptic.

That component of general precession caused by the combined effect of the Moon, the Sun and the planets on the equatorial protuberance of the Earth, producing a westward motion of the equinoxes along the ecliptic about 50’’ per year.
According to an IAU resolution adopted in August 2006, the present terminology replaces lunisolar precession.

See also: → precession; → equator.

The slow motion of the equinoxes along the ecliptic, resulting from the combined motion of the equator (→ precession of the equator) and the ecliptic (→ precession of the ecliptic), or in other words the precession of the Earth’s axis of rotation. Also know as → general precession. The First Point of Aries moves westward along the ecliptic at 50.38 arcseconds per year (1 degree every 71.6 years), causing the equinoxes to occur about twenty minutes earlier each sidereal year. See also → nutation.

See also: → precession; → equinox.

The gradual change in he orbital planes of a binary system.

See also: → precession; → node.

The interval with which a rotating body precesses. The precession period of the Earth is 25,770 years. For a → spinning top it is given by: T_p = (4π²I)/(mgrT_s),

where I is the → moment of inertia, m the mass of the top, g gravity, r the distance between the center of mass and the contact point, and T_s is the spinning period of the top.

See also: → precession; → period.

A time interval over which an orbit precesses by 2π radians in its plane.

See also: → precession; → time.

Of or pertaing to → precession.

See also: → precession; → -al.

The path of either → celestial poles around the → ecliptic pole due to the → precession of equinox. It takes about 26,000 years for the celestial pole to complete path.

See also: → precessional; → circle.

1. Meteo.: Any form of water, such as rain, snow, sleet, or hail, that falls to the Earth’s surface. The quantity of such water falling in a specific area within a specific period.
   
2. Chemistry: The process of separating a solid substance from a solution.

Etymology (EN): From M.Fr. précipitation, from L. præcipitationem “act or fact of falling headlong, haste,” from præcipitare “fall, be hasty,” from præceps “steep, headlong, headfirst,” from præ- “forth” + caput, → head.

Etymology (PE): 1) Bâreš, verbal noun of bâridan “to rain,” bârân “rain;” Mid.Pers. vâritan, vârân; Av. vār- “rain; to rain;” cf. Skt. vār- “rain, water; to rain;” PIE base *uer- “water, rain, river.”
Rizeš, verbal noun of rixtan “to flow, to pour,” → overflow.

2. Tahnešast “to settle down, precipitate,” from
   tah “→ bottom, end;” + nešast past stem of nešastan “to sit down; to settle down; to sink,” → sit.

1. Definitely or sharply stated, or defined.
   

2. Designating → precision.
   

See also: → accurate, → exact.

Etymology (EN): M.E., from M.Fr. précis “cut short” from M.L. precisus, from L. præcisus “abridged, cut off,” p.p. of præcidere “to cut off, shorten,” from præ- “in front,” → pre-,

• cædere “to cut down, chop, beat, hew, slay.”

Etymology (PE): Parsun literally “cut around” (compare with Skt. pariccheda “precise, accurate definition, exact discrimination,” from pari- + cheda “cut, cutting off,” from chid- “to cut, split”), from par-, variant of
pirâ- “around, about,” → peri-, + sun “to cut;” cf. Kurd. Sorani su, sun “to sharpen, whet;” Kurd. Kurmanji (prefixed ha-, contraction of *ham-) hasun “to sharpen, whet;” Mod.Pers. sân “whetstone,” variants fasân, afsân, awsân; Av. si-, sā- “to cut;” cf. Skt. śā- “to sharpen, whet” (see also → concrete).

In a precise manner.

See also: → precise; → -ly.

The quality or state of being very accurate.

See also: → precise; → -ness.

1. The state or quality of being → precise.
   

2. The degree to which repeated measurements of a quantity give the same results under unchanged conditions. Not the same as → accuracy,
   but often confused as such. See → accuracy for the difference between precision and accuracy.

See also: Verbal noun from → precise.

1. A person or thing that comes before another of the same kind; a forerunner.
   

   2. A substance from which another is formed, especially by metabolic reaction (OxforddDctionaries.com)

Etymology (EN): M.E., from L. præcursor “forerunner,” from præcursus, p.p. of præcurrere, from præ- “before,” → pre-, + currere “to run,” → current.

Etymology (PE): Pišgâm, from piš- “before,” → pre-, + gâm “step, pace,”
→ stage.

A component of a → pulsar pulse that appears shortly in advance of the main pulse.

See also: → precursor; → pulse.

1. Act of plundering or robbing; predatory behavior.
   

   2. The preying of one animal on others.

See also: Verbal noun, → prey.

Zoology: Any organism that exists by preying upon other organisms (Dictionary.com).

See also: Agent noun from → prey.

1. Of, or relating to a predator.
   

   2. Living by preying on other living animals.

See also: Agent noun from → prey.

1a) Grammar: The part of a → sentence or → clause stating something about the → subject and usually consisting of a → verb. For example, in the sentence “The man opened the door,” the subject is “the man” and the predicate is “opened the door.”

1b) Logic: Something which is affirmed or denied concerning the subject in a → proposition.

1c) Math.: A → function whose values are statements about n-tuples of objects forming the values of its → arguments. For n =1 a predicate is called a “property” , for n> 1 a → relation; propositions may be regarded as zero-place predicates (encyclopediaofmath.org).

2a) To state, affirm, or assert (something) about the subject of a proposition.

2b) To make (a term, expression, etc.) the predicate of a proposition.

Etymology (EN): M.E., from M.Fr. predicat, from L. praedicatus “declared, proclaimed,” p.p. of praedicare, from prae “beforehand,” → pre-,

• dicare “proclame,” from stem of dicere “to speak, to say,” from PIE root *deik- “to point out, to show,” cognate with Pers. dis, → form, and andišidan, → think.

Etymology (PE): Farâsan from farâ- “before; toward, along; above, upon, over,” → pro-, + san Proto-Ir. *sanh- “to declare, explain,” related to soxan, → speech and pâsox, → response, sahân, → sentence.

The generic term for systems of → formal logic like → first-order logic and → second-order logic. Predicate logic contains → variables which can be quantified (→ quantify, → quantification).

See also: → predicate; → logic.

In a → formal language, a letter used to describe a → predicate or → relation. Also called → relation symbol.

See also: → predicate; → symbol.

To like better or value more highly.

Etymology (EN): M.E. preferre, from O.Fr. preferer and directly from L. praeferre “to place or set before, carry in front,” from prae “before,” → pre-, + ferre “to carry, to bear,” from PIE root *bher- “to carry;” cf. Pers. bordan “to carry, bear,” → refer.

Etymology (PE): Behzunidan, literally “to value highly, to consider better,” from beh “good, fine,” → optimum,

• zun, variant of dân-, dânestan “to know, consider,” cf. Tâti zun/zund “to know,” Khunsâri zûn-/zûnâ, Mahallâti zôn-, Semnâni -zûn-, Hamedâni zunayän/zun- , Esfahâni zunän/zun-, Yarandi zônâj-/zôn-, Gazi zûn-/zûnâšt;
  Av. zān- “to know,” → science.

Worthy to be preferred; more desirable.

See also: → prefer; → -able.

1. Act of → preferring.
   

   2. That which is preferred.

See also: → prefer; → -ence.

An → affix that is placed before a base to denote a modified meaning or make another word.

See also: → pre-; → affix.

Carefully chosen uniform exposure of a detector. For CCD this can be used to overcome the deferred charge phenomenon; in photography this helps bring dim images to a comfortably high density.

See also: → pre- + → flash.

1. Philosophy: To apprehend with or without conscious formulation or cognition of the perceived object; to interact in time and space with an object or event (Oxford Dictionary, lexico.com).
   

   2. (obsolete) To sieze.

Etymology (EN): From L. prehendere “to seize,” from prae- “before,” → pre-, + -hendere , from PIE root *ghend- “to seize, take,” root of Gk. khandanein “to hold, contain;” Lith. godetis “be eager;” Welsh gannu “to hold, contain;” Russian za-gadka “riddle;” Old Norse geta “to obtain, reach; to be able to;” E. get.

Etymology (PE): Nutidan, from nut-, from Yaghnobi nôta “to take,” from Sogd. niyât “to take, grasp,” from Proto-Ir. *ni-yāta-, from *iam- “to take, to hold;” cf. Av. yam- (yās-) “to hold, keep;” O.Pers. yas- “to strech, reach out;” Skt. yam- “to hold, restrain” (Cheung 2007).

1. Zoology Psychology: The action of grasping or seizing.
   

   2. Philosophy: An interaction of a subject with an event or entity which involves perception but not necessarily cognition (Oxford Dictionary, lexico.com).

See also: Verbal noun of → prehend.

Preceding and leading up to the main part, matter, or business; introductory; preparatory (Dictionary.com).

Etymology (EN): From Fr. préliminaire, from M.L. praeliminaris, from L. prae- “before,” → pre-,

• limen “threshold.”

Etymology (PE): Pišâstâni, literally “before the threshold,” from piš, → pre-, + âstâni, of or pertaining to âstân, → threshold.

Logic: An initial → proposition or statement that is known or assumed to be → true and on which a logical → argument is based.

Etymology (EN): From M.E. premiss, from O.Fr. premisse, from M.L. premissa (propositio) “(the proposition) set before,” feminine p.p. of L. praemittere “send or put before,” from prae “before,”
→ pre-, + mittere “to send,” → mission.

Etymology (PE): Pišpâyé, from piš-, → pre-, + pâyé, → base.

In → particle physics, any of postulated “point-like” particles from which are composed → quarks and → leptons. In other words, preon models assume there is a more fundamental kind of particle than those so far known. Different preon models consider different numbers and different natures of the preons.

See also: Coined by Jogesh Pati and Abdus Salam in 1974, from → pre- + → -on.

A short-lived transition object between the → asymptotic giant branch (AGB) and → planetary nebula phases. See also
→ post-asymptotic giant branch star (post-AGB).

See also: → pre-; → planetary; → nebula. The more commonly used term, → protoplanetary nebula, is a misnomer and must be avoided. Indeed → protoplanetary is widely used to refer to disks around → pre-main sequence stars. Since the term → protoplanet is used to denote planets undergoing formation, the use of the term “protoplanetary nebula” to mean a completely different kind of object is an unfortunate choice (Sahai et al. 2005, ApJ 620, 948).

A word used with a noun or pronoun to mark its relation with another word.

Etymology (EN): From L. praepositionem “a putting before,” from praepositus, p.p. of praeponere “put before,” from prae “before,” → pre-, + ponere “put, set, place,” → position.

Etymology (PE): Pišhel, from piš-, “before,” → pre-, + hel-, helidan, heštan “to place, put,” → leap.

An advance printing, usually of an article in a periodical.

See also: → pre-; → print.

Relating to a stage or time prior to the rise of modern science and to the application of the → scientific method.

See also: → pre-; → scientific.

1. To lay down, in writing or otherwise, as a rule or a course of action to be followed; appoint, ordain, or enjoin.
   

2. Medicine: To designate or order the use of a medicine, remedy, treatment, etc. (Dictionary.com).

See also: → pre-; + scribe, → inscribe.

1. An act of prescribing.
   

2. A direction, usually written, by the physician to the pharmacist for the preparation and use of a medicine or remedy. The medicine prescribed (Dictionary.com).

See also: Verbal noun of → prescribe; → -tion.

1. That prescribes; giving directions or injunctions.
   

2. Depending on or arising from effective legal prescription, as a right or title established by a long unchallenged tenure (Dictionary.com).

See also: → prescribe; → -ive.

The state or fact of being present.

See also: Noun from → present.

1. Being, existing, or occurring at this time or now.
   

2. At this time; at hand; immediate.
   

3. Grammar: Noting an action or state occurring at the moment of speaking.

Etymology (EN): M.E., from O.Fr. present, from L. præsentem (nominative præsens) “present, immediate,” from pr.p. of præesse “to be before, to be at hand,” from præ- “before,” → pre-, + esse “to be;” cf. Pers. ast “is,” hastan, astan “to be;” O.P. ah- “to be,” astiy “is;” Av. ah- “to be,” astī “is;” Skt. as- “to be,” ásti “is;” Gk. esti “is;” PIE base es- “to be.”

Etymology (PE): Pišâst, on the model of L. præesse, as above, from piš, → pre-, + epenthetic -â- + ast “is,” variants hast, hi, has (Qâyen), isâ (Rašt), a (Aftar), heye (Kurd.); Av./O.Pers. ah- “to be,” Proto-Ir. *Hah- “to be,” → existence.
Bâšandé agent noun from budan “to be;”
→ condition.
Konuni “presently,” from konun, aknun “now, present,” from *hak-nun, from *hak-, cf. Av. hakat- “at once, immediately” + nū- “now” (Mid/Mod.Pers. nun “now, at present”); Av. nūrəm “now;” O.Pers.
nūram “now;” Skt. nú- “now, just, but,” nūnám “now, at present, indeed;” Gk. nun “now;” L. nu- “now” (in nu-dis “the day after tomorrow”); Goth. nu “now;” O.E. nu; E. now; PIE base *nu- “now.”

Same as → present epoch, → today, → current cosmological epoch.

See also: → present; → day.

Same as → present day, → today, → current cosmological epoch.

See also: → present; → epoch.

A → participle that indicates an ongoing action or state in the present.

See also: → present; → participle.

The present number of stars on the → main sequence per unit logarithmic mass interval per square parsec. The PDMF is the basis for deriving the → initial mass function (IMF).
This mass function is not corrected for stellar evolution nor losses through stellar deaths.

See also: → present; → day; → mass; → function.

To occupy the place of authority or control, as in an assembly or meeting; act as president or chairperson (Dictionary.com).

See also: → pre-; → reside.

1. The highest executive officer of a modern republic, as the Chief Executive of the United States (often initial capital letter).
   

2. An officer appointed or elected to preside over an organized body of persons (Dictionary.com).

Etymology (EN): → preside; → -ent.

Etymology (PE): Farneštgâr, from farnešt, present stem of farneštidan, → preside, + agent noun suffix -gâr, → -or, on the model of âmuzgâr “teacher.”

Of or relating to an epoch earlier than the formation of the Sun.

See also: → pre-; → solar.

A → refractory → nanoparticle embedded in → meteorites and → interplanetary dust particles whose → isotopic ratios suggest formation earlier than the Solar System.

See also: → presolar; → grain.

A mathematical analysis, based on → self-similarity, used to predict the → mass function of spherically collapsing → dark matter halos. The formalism assumes that the fraction of mass in halos more massive than M is related to the fraction of the volume in which the smoothed initial density field is above some threshold δ_cρ, where ρ is the average density of the Universe, with the volume encompassing a mass larger than M. A variety of smoothing → window functions and thresholds have been argued, but the most common is a top-hat window
in real space and δ_c≅ 1.69. The Press-Schechter formalism provides a relatively good fit to the results of numerical simulations in cold dark matter theories.

See also: First described by William H. Press and Paul Schechter’s paper (1974, ApJ 187, 425); → formalism.

The force per unit area.

Etymology (EN): M.E., from O.Fr. pressure, from L. pressura “action of pressing,” from pressus, p.p. of premere “to press, compress.”

Etymology (PE): Fešâr “squeezing, constriction, compression,” verb fešordan, fešârdan “to press, squeeze;” phonetic variants Lori xošâr, Aftari xešâr, Qazvini, Qomi xošâl; cf. Khotanese ssarr- “to exhilarate;” loaned in Arm. ôšarak, in Ar. afšaraj “juice.”

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.

See also: → 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.

See also: → pressure; → gradient.

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

See also: → pressure; → gradient; → force.

A physical state of dense matter in which the electrostatic field of one atom should influence a neighboring atom and hence disturb atomic levels. In extreme case, such as white dwarfs, electron clouds practically rub and electrons are ionized off the parent atoms.

See also: → pressure; → ionization.

Same as → p mode

See also: → pressure; → mode.

A basic ingredient of the → mixing length theory that scales with the → mixing length. It is defined by the relation: H_P = -dr/dln P = -Pdr/dP , where r is the height and P the pressure. See also → scale height.

See also: → pressure; → scale; → height.

Occurring before something else in time or order.

Etymology (EN): From L. praevius “leading the way,” from prae-,
→ pre- + via “way.”

Etymology (PE): Pišin, from piš “before,” → pre-.

Coming or occurring before something else; prior.

See also: → previous; → -ly.

A statement concerned with thermodynamic heat exchange, according to which bodies in → thermal equilibrium are simultaneously absorbing and emitting radiant energy. A body radiates in the same way whether other bodies are present or not. Also called Prevost’s theory of exchanges.

See also: Named after Pierre Prévost (1751-1839), a Swiss philosopher and physicist, who, in 1791, put forward the statement; → law; → exchange.

1. To seize and devour prey, as an animal does.
   

   2. An animal hunted or seized for food, especially by a carnivorous animal (Dictionary.com).

Etymology (EN): M.E. preye, from O.Fr. preie, from L. praeda “booty, plunder, game hunted;” ultimately from prehendere “to grasp, seize.”

Etymology (PE): 1) Cavidan, related to Khotanese cev- “to get, seize,” Ossetic cævyn, cavd “to hit, to strike,” Pers. câpidan “to plunder,” cafsidan, caspidan “to stick; to plunder;” Proto-Ir. *cap- “to seize.”

2. Cavâk, from cav- present stem of cavidan, as above,

• -âk suffix denoting object of an action.

An animal that is hunted and killed by a → predator as food.

See also: → prey; → animal.

The concentric colored rings formed by an electrical → spark when a → discharge takes place on a metallic plate.

See also: Joseph Priestley (1733-1804), English chemist, author, and clergyman; → ring.

1. First or highest in rank or importance; chief; principal.
   

2. Abbreviation for → primary body, → primary star, or → primary mirror.

Etymology (EN): M.E., from L. primarius “of the first rank, principal,” from primus “first.”

Etymology (PE): Naxostân, from
naxost, from Mid.Pers. naxust “the first,” Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx “beginning” + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

The body that is being orbited; such as the → Sun in the → solar system. As regards → multiple star systems, the most massive, or → primary star. See also: → secondary body.

See also: → primary; → body.

A → cell in which the electrochemical action producing the current is not normally reversible. Such a cell cannot be recharged by an electric current. → secondary cell.

See also: → primary; → cell.

The → cosmic rays which arrive on the Earth’s → atmosphere from the outer space. The primary cosmic rays are very high energy → protons and to a lesser extent heavier nuclei which rain upon the Earth from all diretions in the outer space. They contain about 90% protons, 7% → alpha particles and about 1% still heavier nuclei of amost all the atoms from Li to Ni ( → mass number< 60). See also: → secondary cosmic rays.

See also: → primary; → cosmic; → ray.

Of a transiting → exoplanet, the event and the interval of time during which the planet passes in front of its host star. The planet occults a portion of the stellar disk, and a fraction of light from the star is seen after traversal through the atmosphere around the planet’s limb. → secondary eclipse.

See also: → primary; → eclipse.

In a → reflecting telescope, the first mirror that collects the light and focuses it to the → focal plane.

See also: → primary; → mirror.

The main rainbow that forms between about 40° and 42° from the → antisolar point (or about 50° from the → antisolar point), as viewed by the observer. The light path involves → refraction and a → single  → reflection inside the water → droplet. If the drops are large, 1 millimeter or more in diameter, red, green, and violet are bright but there is little blue.

As the droplets get smaller, red weakens.

Rainbows are not seen in midday since the whole 42° circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the Sun is illuminating from the west.

See also: → primary; → rainbow.

In a → multiple star system, the most massive → component. In other words, the star nearest to the system’s → center of garvity.

See also: → primary; → star .

1. Of the first importance; of the highest rank.
   

2. Same as → prime number.

Etymology (EN): M.E., from L. primarius “of the first rank, principal,” from primus “first.”

Etymology (PE): Naxost, naxostin, naxosti, from
Mid.Pers. naxust “the first,” Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx “beginning” + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

The focal point of a large primary reflecting mirror. This focus actually falls at a point just within the upper structure of the telescope and provides a large field of view.

See also: → primary; → focus.

The meridian at which longitude is defined to be 0°. The meridian running through Greenwich.

See also: → primary; → meridian.

A number which is divisible by no whole number other than itself and one.

See also: → prime; → number.

The great circle through the observer’s zenith that
intersects the horizon at the west and east points. → vertical circle.

See also: → primary; → vertical.

Lemaître’s (1931) name for the early dense Universe, which later became known as the → Big Bang theory.

See also: From L. primaevus “early in life,” from primus “first,” → prime, + aevum “an age,” + → -al; → atom.

Pertaining to or existing at or from the very beginning.

Etymology (EN): From L.L. primordialis “first of all, original,” from L. primordium “the beginning,” from primus “first” + stem of ordiri “to begin.”

Etymology (PE): Bonâqâzin, from bon “basis; root; foundation; bottom” (Mid.Pers. bun “root; foundation; beginning,” Av. būna- “base, depth,” cf. Skt. bundha-, budhná- “base, bottom,” Pali bunda- “root of tree”)

• âqâzin “pertaining to the beginning,” from âqâz “beginning” (Proto-Iranian *āgāza-, from prefix ā-
• *gāz- “to take, receive,” cf. Sogdian āγāz “beginning, start,” pcγz “reception, taking”).

The relative amount of a light element (e.g. deuterium, lithium, helium) synthesized in the early Universe.

See also: → primordial; → abundance.

A black hole formed following the Big Bang event due to incredibly violent turbulence that squeezed concentrations of matter to high densities. These black holes, first suggested by
Stephen Hawking, are expected to have a mass comparable to that of a mountain and a size as small as an atom. Same as → mini black hole.

See also: → primordial; → black hole.

In cosmological models, the phenomenon that is supposed to seed the → cosmic microwave background anisotropies and the structure formation of the Universe.

See also: → primordial; → curvature; → perturbation.

A high redshift, metal-deficient galaxy that formed very early in the history of the Universe.

See also: → primordial; → galaxy.

The helium element created in the → early Universe, around 3 minutes after the → Big Bang, when the temperature dropped to 10⁹ degrees; in contrast to the helium being synthesized in stars.

Based on observations of helium → emission lines in → H II regions of metal-poor dwarf galaxies (→ metal-deficient galaxy), the primordial ⁴He → chemical abundance (by mass) is estimated to be Y_P = 0.24672 ± 0.00017. Moreover, using observations of a near-pristine → intergalactic cloud, a value of
0.250 ^+0.033_-0.025 has been reached
(Cooke & Fumagalli, 2018, Nature Astronomy, 2, 657). The theoretical He abundance predicted by → Big Bang nucleosynthesis is
0.24709 ± 0.00017 (Pitrou et al., 2018, arXiv:1801.08023).

See also: → primordial; → helium.

The formation of → chemical elements in the → early Universe, between about 0.01 seconds and 3 minutes after the → Big Bang, when the nuclei of primordial matter collided and fused with one another. Most of the → helium in the → Universe was created by this process. Same as → Big Bang nucleosynthesis

See also: → primordial; → nucleosynthesis.

First or highest in rank, importance, value, etc. See also → main.

Etymology (EN): M.E., from O.Fr. principal, from L. principalis “first in importance,” from princeps “first, chief, prince,” literally “that takes first,” from primus “first” + root of capere “to take.”

Etymology (PE): Farin literally “foremost,” from far-, Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā “forth,” pouruua- “first;” cf. Skt. pūrva- “first,” pra- “before, formerly;” Gk. pro; L. pro; O.E. fyrst “foremost,” superlative of fore, E. fore + -in superlative suffix.

1. Optics: Any imaginary line passing through the center of curvature of a → spherical mirror or → lens and the corresponding geometrical center.

Principal axis is perpendicular to the mirror or lens at the pole. Rays of light parallel to the principal axis of a → concave mirror

will appear to converge on a point in front of the mirror somewhere between the mirror’s pole and its center of curvature. Same as → optical axis.

2. Mechanics: One of three mutually perpendicular axes of an object about which the → moment of inertia is maximum or minimum.

More specifically, an object has an infinite number of moments of inertia. If an object is not symmetrical about all planes through its → center of mass, then there will be one → axis of rotation about which the moment of inertia is largest, and there will be one axis of rotation about which the moment of inertia is smallest. These two axes will always be perpendicular to each other and are the principal axes of the object. The third principal axis of an object is the axis perpendicular to these two axes.

In general the → angular momentum (L) of a body spinning about a point O is not in the same direction as the axis of rotation, or that of the → angular velocity angular velocity (ω); that is L is not parallel to ω. For certain bodies, however, there can be certain axes for which L and ω are parallel. In that case L = Iω, where I is the moment of inertia about the axis in question.

In a symmetric rigid body, the axes of symmetry coincide with the principal axes of the moment of inertia

See also: → principal; → axis.

In atomic physics, the first of a set of quantum numbers which describe an atomic orbital. Symbolized as n, it characterizes the size and energy of an orbital.

See also: → principal; → quantum;
→ number.

A fundamental, primary assumption, or general law from which others are derived.

Etymology (EN): From M.E., from O.Fr. principe, from L. principium “a beginning, first part,” from princeps “first, chief, prince,” literally “that takes first,” from primus “first” + root of capere “to take.”

Etymology (PE): Parvaz “origin, root, stock” (as used in particular by Ferdowsi); cf. Av. fra-vāza- “drawing from; leading onward,” from Av. fra-, frā- “before; forward, forth” (fratəma- “first, front,” pouruua- “first,” fra-cara- “preceding;”
O.Pers. fra- “forward, forth;” Mid.Pers. fra-;
cf. Skt. pra- “before, formerly,” prathama- “earliest, initial,” pūrva- “first;” Gk. pro; L. pro; O.E. fyrst “foremost,” superlative of fore)

• vaz- “to draw, guide; bring; possess; fly; float,” vazaiti “guides, leads”
  (cf. Skt. vah- “to carry, drive, convey,” vahati “carries,”
  pravaha- “bearing along, carrying,” pravāha- “running water, stream, river;” L. vehere “to carry;” O.E. wegan “to carry;” O.N. vegr; O.H.G. weg “way,” wegan “to move,” wagan “cart;” M.Du. wagen “wagon;” PIE base *wegh- “to drive;” see also → flight).

Newton’s third law of motion, which states that for every action there must be an equal and opposite reaction.

See also: → principle; → action; → reaction.

The second postulate in Einstein’s theory of → special relativity whereby the → velocity of light in → vacuum has the same absolute value in all → inertial reference frames irrespective of the direction and speed of propagation of the light source. It should be emphasized that this constancy of the speed of light holds among → reference frames moving uniformly with respect to each other. An observer accelerated with respect to a light source will measure a speed of light that is smaller than the speed of light measured in a → rest frame. See also → principle of relativity.

See also: → principle; constancy, noun related to → constant.

In special relativity, the principle that the laws of physics take the same mathematical form in all inertial frames of reference.

See also: → principle; → covariance.

In → general relativity the principle
which states that in the immediate proximity of an → accelerating system the acceleration is physically equivalent to → gravitational force.
This principle also implies the equivalence of → gravitational mass and → inertial mass. Same as the → equivalence principle. See also → Einstein’s elevator.

See also: → principle; → equivalence.

The second principle of → formal logic introduced in Aristotle’s theory of the → syllogism: A
statement is either → true or → false. In other words, two → contradictory → propositions cannot both be true. The truth of one implies the falsehood of the other. Also called law of excluded middle and → principle of excluded third.

See also: → principle; → exclude; → middle.

Same as → principle of excluded middle.

See also: → principle; → exclude; → third.

The first principle of → formal logic introduced in Aristotle’s
theory of the → syllogism: If a statement is true then it is true. Also called → law of identity.

See also: → principle; → identity.

The principle that, for a system whose total mechanical energy is conserved, the path to be taken for the system from one configuration to another is the one whose action has the least value relative to all other possible paths and from the same configurations. Also called Maupertuis’ principle, least-action principle.

See also: → principle; → least; → action.

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.

See also: → principle; → non-; → contradiction.

One consequence of the theory of → special relativity, according to which no two events separated by a distance greater than their separation in time multiplied by the → speed of light may have a → causal influence on each other. Violation of this principle leads to → paradoxes, such as that of an → effect preceding its → cause.

See also: → principle; → relativistic; → causality.

The first postulate in Einstein’s theory of → special relativity whereby all the laws of physics are the same in every → inertial reference frame. In other words, no physical measurement can distinguish one inertial reference frame from another. See also → principle of constancy.

See also: → principle;
→ relativity.

1a) The state of being printed.

1b) Printed lettering, especially with reference to character, style, or size.

1c) Printed material; a printed publication, as a newspaper or magazine.

2a) To produce (a text, picture, etc.) by applying inked types, plates, blocks, or the like, to paper or other material either by direct pressure or indirectly by offsetting an image onto an intermediate roller.

2b) To reproduce (a design or pattern) by engraving on a plate or block.

2c) To form a design or pattern upon, as by stamping with an engraved plate or block.

2d) To cause (a manuscript, text, etc.) to be published in print (Dictionary.com).

Etymology (EN): M.E. prent(e), print(e), prient(e), from OF priente “impression,” noun use of feminine p.p. of preindre “to press,” from L. premere “to press, hold fast.”

Etymology (PE): Câp “press,” loan from Indo-Aryan languages chapa, chháp, chāp “seal, stamp, impression.”

1. A person or thing that prints, especially a person whose occupation is printing.
   

2. Computers: An output device that produces a paper copy of alphanumeric or graphic data (Dictionary.com).

See also: → print; → -er.

A font used for printing. See also → screen font.

See also: → printer; → font.

1. Preceding in time or in order; earlier or former; previous.
   

2. Preceding in importance or privilege.

Etymology (EN): O.E., from M.L. prior “former, previous, first, superior,” comparative of O.L. pri “before,” from PIE *prai-, *prei-, from root *per- “forward, through,” → pro-.

Etymology (PE): Parin, from pra-, fra- “before, forward, forth,” cognate with Gk. and L. → pro-.

The condition or quality of being earlier in time or occurrence, or being regarded as more important.

See also: → prior; → -ity.

Optics:
A transparent solid body, having at least two polished plane faces inclined relative to each other, from which light is reflected or through which light is refracted.
Geometry: A solid having two faces lying in parallel planes and with the other faces parallelograms.

Etymology (EN): L.L. prisma, from Gk. prisma, literally “something sawed,” from prizein “to saw.”

Etymology (PE): Manšur, etymology not clear, may be related to Ar. mawšur “prism,” of unknown origin.

The angle between the faces on which light is incident and from which it emerges.

See also: → prism; → angle.

An optical device consisting of a pair of small telescopes mounted side by side, each telescope having two prisms between the eyepiece and objective for erecting the image.

See also: → prism; → binoculars.

An ocular equipped with a prism that forms an upright image in an astronomical telescope.

See also: → prism; → ocular.

An instrument used to determine the precise timing of a star’s passage across a vertical circle.
It is used for making precise determinations of the positions of stars and planets, and can be used inversely to determine the latitude and longitude of the observer, assuming the star positions are accurately known. It consists of an accurate prism, a small pool of mercury to serve as an artificial horizon.
The most notable example of this type of instrument is that of → Danjon astrolabe.

See also: Adj. of → prism + → astrolabe.

The spectrum formed by a dispersing prism or a dispersing prism system.

See also: Adj. of → prism + → spectrum.

The state of being private.

See also: Noun from → private.

Pertaining to or affecting a particular person or a small group of persons; individual; → personal (Dictionary.com).

Etymology (EN): L. privatus “set apart, peculiar, personal,” used in contrast to publicus, p.p. of privare “to separate, deprive, to rob” from privus “one’s own, individual.”

Etymology (PE): Vâvan, literally “separated, not bound,” from vâ- separation prefix,
→ de-, + van, contraction of vand, band, from vastan, bastan “to bind, fasten, close,” → band.

The transfer from public to private ownership.

See also: → private; → -tion.

To transfer from public to private ownership and control.

See also: → private; → -ize.

A special right, advantage, or immunity granted or available only to a particular person or group (OxfordDictionaries.com).

Etymology (EN): M.E., from O.Fr. privilege “right, priority, privilege” and directly from L. privilegium “law applying to one person, bill of law in favor of or against an individual,” from privus “individual,” → private.

Etymology (PE): Fardâré, from far- intensive prefix “much, abundant; elegantly,” → perfect, + dâr present stem of dâštan “to have, possess,” → property, + noun/relation suffix -é.

Having special rights, advantages, or immunities.

See also: Adjective from → privilege.

A prefix of priority in space or time having especially a meaning of advancing or projecting forward or outward.

Etymology (EN): From L. pro “in favor of, in place of, before, for,” also in some cases from cognate Gk. pro “before, in front of,” both from PIE base *por- “forward, through;” cf. Pers. farâ-, as below; Gk. para- “from beside, against, beyond;” Goth. faura “before,” O.E. fore “before, for, on account of.”

Etymology (PE): Farâ- “forward, along; above, upon, over; before, foremost, opposing, facing,” variant far- intensive prefix “much, abundant; elegantly,” from Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā, fərā-, fra- “forward, forth; before; excessive” (fratəma- “first, front,” pouruua- “first,” fra-cara- “preceding”);
cf. Skt. prá- “before; forward, in fron,” prathama- “earliest, initial,” pūrva- “first;” Gk. pro; L. pro, as above.

1. General: The quality or fact of being probable. A strong → likelihood or chance of something.
   

2. Statistics: The branch of → mathematics that studies the possible outcomes of given events and their relative distributions. → probability theory.

See also: From → probable + → -ity.

A curve that describes the distribution of probability over the values of a random variable.

See also: → probability; → curve.

A mathematical function whose integral over any interval gives the probability that a continuous → random variable has values in this interval. Also known as → density function, frequency function, → probability function.

See also: → probability; → density; → function.

The function that describes the range of possible values that a random variable can attain and the probability that the value of the random variable is within any (measurable) subset of that range.

See also: → probability; → distribution.

A function that represents a probability distribution in terms of integrals. Also called probability density function or density function.

See also: → probability; → function.

A branch of → mathematics with its own axioms and methods, which is based on the concept of → randomness and is concerned with the possible outcome of given → events and their relative → likelihoods and → distributions.

See also: → probability; → theory.

Likely to happen or to be true; likely but uncertain.

Etymology (EN): From O.Fr. probable, from L. probabilis “provable,” from probare “to try, to test, to prove worthy,” from probus “worthy, good, upright, virtuous,” from PIE *pro-bhwo- “being in front,” from *pro-, extended form of base *per- (cf. Pers. farâ “forward, front”), + base *bhu- “to be” (cf. Pers. budan “to be”).

Etymology (PE): Šavânâ (on the model of tavânâ “able, strong”, from tav- “to be able”), from šow- present stem of šodan “to become, to be, to be doing, to go, to pass,” from Mid.Pers. šudan, šaw- “to go;” Av. š(ii)auu-, šiyav- “to move, go,” šiyavati “goes,” šyaoθna- “activity; action; doing, working;” O.Pers. šiyav- “to go forth, set,” ašiyavam “I set forth;” cf. Skt. cyu- “to move to and fro, shake about; to stir,” cyávate “stirs himself, goes;” Gk. kinein “to move;” Goth. haitan “call, be called;” O.E. hatan “command, call;” PIE base *kei- “to move to and fro.”

A deviation from the population mean μ such that 50% of the observations may be expected to lie between μ - PE and μ + PE. For the normal distribution, the probable error is 0.6745 times the standard deviation.

See also: → probable; → error.

1. (n.) An exploratory action or device for investigating and obtaining information on a remote region.
   Same as → space probe. → lunar probe.
   
2. (v.) To conduct a thorough investigation of something.
   To examine or explore with a probe.

Etymology (EN): M.L. proba “examination, test,” L. probare “to test, prove worthy,” from probus “worthy, good, upright.”

Etymology (PE): 1) Gomâné “a shaft sunk in order to ascertain the depth of the water when making a subterraneous canal,” from Proto-Iranian *vi-mā-, from vi- “apart, away from, out” (cf. Av. vi-; O.Pers. viy- “apart, away;” Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + mā- “to measure” (cf.
O.Pers./Av. mā(y)- “to measure;” Mod.Pers.
mâ/mun/mân “measure,” as in Pers. terms âzmâ- “to test;”
pirâmun “perimeter,” âzmun “test, trial,”
peymân “measuring, agreement,” peymâné “a measure; a cup, bowl;”
PIE base *me- “to measure;”
cf. Skt. mati “measures,” matra- “measure;” Gk. metron “measure;” L. metrum).
2) Gomâné zadan composite infinitive of gomân with zadan

“to strike, beat; to play an instrument; to do” (Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- “to strike, hit, smite, kill” (jantar- “smiter”); cf.
Skt. han- “to strike, beat” (hantar- “smiter, killer”);
Gk. theinein “to strike;” L. fendere “to strike, push;” Gmc. *gundjo “war, battle;” PIE *g^when- “to strike, kill”).

1. Any question or matter involving doubt, uncertainty, or difficulty.
   

2. Math.: A statement requiring a solution, usually by means of a mathematical operation or geometric construction.

Etymology (EN): M.E., from O.Fr. problème, from L. problema, from Gk. problema “a problem, a question,” literally “thing put forward,” from proballein “to propose,” from → pro- “forward” + ballein “to throw,” → ballistics.

Etymology (PE): Parâsé, from pərəs- present tense stem of Av. fras- “to ask, question, inquire,” pərəsaiti “asks,” to which is related Mod.Pers. pors-, porsidan “to ask;” Mid.Pers. pursidan; O.Pers. prs-, fraθ- “to ask, examine, investigate, punish;” Sogd. anfrāsē “question, enquiry;” cf. Skt. praś- “to ask, long for;” Tokharian prak-/prek- “to ask;” L. prex “request,” precor “to ask, to pray;” Lith. prašyti “to ask, to demand;” Ger. fragen “to ask;” PIE base *prek- “to ask.”

1. Posing a problem; difficult to solve.
   

   2. Open to doubt; debatable.
      

   3. Not settled; unresolved or dubious (TheFreeDictionary.com).

See also: From M.Fr. problematique, from L. problematicus, from Gk. problematikos “pertaining to a problem,” from → problem.

An act or a manner of proceeding in any action or process; a particular course or mode of action.

Etymology (EN): From Fr. procédure “manner of proceeding,” from O.Fr. procédér from L. procedere “to go forward, advance,” from → pro- “forward” + cedere “to go.”

Etymology (PE): Ravand “going,” from raftan “to go, walk;” Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack.”

1. (n.) A series of actions directed toward a specific aim.
   A series of natural occurrences that produce change or development.
   
2. (v.) To treat or prepare something in a series of steps or actions.

Etymology (EN): M.E., from O.Fr. proces, from L. processus “advance, progress,” from p.p. stem of procedere “go forward,” from → pro- “forward” + cedere “to go.”

Etymology (PE): 1) Farâravand, from farâ- “forward” → pro- + ravand, contraction of ravandé “goer, going,” from raftan “to go, walk;” Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack.”

Note: Another Pers. equivalent for process (n.), coined by the Mosâhab group on the model of the L. concept, is farâyand (فر‌آیند). This dictionary has not retained farâyand, because it is problematic and even contradictory, as first remarked by M.Sch. Adib-Soltani. The process notion denotes a forward motion, composed of two components indicating the same direction “moving forward.” In contrast,
farâyand implies two opposite, contrary vectors, farâ- “forward” and âyand “coming, comer,” from âmadan “to come.” In brief, farâyand would mean “coming in front of, before, into the presence, in advance of,” while in contrast farâravand means “to go on, to proceed.”

2. Ãmudan, âmâyidan “to prepare, to fashion; to cause to be made;” from Proto-Iranian *ā-mā-; cf. O.Pers./Av. mā(y)- “to measure;” Mod.Pers. mâ/mun/mân “measure,” as in Pers. terms âzmâ- “to test;” pirâmun “perimeter,” âzmun “test, trial,” peymân “measuring, agreement,” peymâné “a measure; a cup, bowl;” PIE base *me- “to measure;”
   cf. Skt. mati “measures,” matra- “measure;” Gk. metron “measure;” L. metrum.

Performing some predefined sequence of operations on an input to produce an output. → data processing;
→ image processing .

See also: Noun of the verb → process.

The act of moving along or proceeding in orderly succession or in a formal and ceremonious manner, as a line of people, animals, vehicles, etc (Dictionary.com).

See also: Verbal noun from → process.

Computers: A central processing unit.
A program that translates another program into a form acceptable by the computer being used. → data processor; → microprocessor

See also: Agent noun of the verb → process.

1. To announce or declare in an official or formal manner.
   

2. To announce or declare in an open or ostentatious way (Dictionary.com).

See also: → pro-; → claim.

The brightest star in the constellation → Canis Minor. With an → apparent visual magnitude of 0.34, Procyon is the eighth brightest star in the night sky. It is actually a → binary star system, consisting of a white → main sequence star of → spectral type F5 IV-V, named Procyon A, and a faint → DA white dwarf companion, named Procyon B. The distance of the system is 11.46 → light-years
and the revolution period about 40 years. Procyon A is of
→ solar metallicity. It has an → effective temperature of about 6600 K and a mass of 1.43 M_sun. The age of the white dwarf is estimated to be 1.7 Giga years. Also called Procyon A, HR 2943, HD 61421 (see Chiavassa et al. 2012, arXiv:1201.3264 and references therein).

Etymology (EN): Procyon, literally “before the dog,” referring to the mythical dog, → Canis Minor, from L. from Gk. prokyon, from → pro- “before” + kyon, kuon “dog;” cognate with Pers. sag, as below.

Etymology (PE): Farâsag, from farâ- “before,” → pro-, + sag “dog;” Mid.Pers. sak/sag Av. spā-; cf. Skt.
svā-; Gk. kuon; L. canis (Fr. chien);
Arm. šun; O.E. hund; O.H.G. hunt; O.Ir. cu; Welsh ci; Rus. sobaka;
PIE *kwon-. In several Pers. dialects this term has conserved its older Av.
form with respect to its Modern “official” counterpart: Tâleši, Tâti: espa; štiyâni: esb; Kâšâni, Sorxeyi: esbâ;
Lâsgardi: aesbae.

1. A thing that is made or created (by a person, machine, or natural process).
   

2. Chemistry: A substance resulting from a chemical reaction.
   

3. Math.: The result of the → multiplication of two or more quantities.

Etymology (EN): From M.E., from L. productum “something produced,” noun use of neuter p.p. of producere “bring forth,” → production.

Etymology (PE): Farâvardé, farâvard, p.p. of farâvardan “to produce;” → production.

The act of producing; creation; something that is produced; a product. → pair production

Etymology (EN): M.E., from O.Fr. production, from M.L. productionem, from L. productus, p.p. of producere “bring forth,” from → pro- “forth” + ducere “to bring, lead.”

Etymology (PE): Farâvareš “bringing forth,” from far- “forth,” → pro-,

• âvareš, “bringing,” verbal noun âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).

An occupation, especially one that requires prolonged training and a formal qualification.

Etymology (EN): From M.E., from O.Fr. profession, from L. professionem “public declaration,” from professus “having declared publicly,” ultimately from → pro- “forth” + fateri “to acknowledge, confess.”

Etymology (PE): Pišé “profession, job,” from Mid.Pers. pêšak “profession, job, work; class, group;” Av. pištra- “occupation; class, group,” from paēs- “to paint; to adorn,” paēsa- “adornment;” Mid.Pers. pēsīdan “to adorn;” O.Pers. pais- “to adorn, cut, engrave;” Mid.Pers. bišt-, bis- (nibištan, nibes- “to write”), Mod.Pers -vis, -veš (in nevis-, neveštan “to write”), pisé “variegated;” cf. Skt. piśáti “adorns; cuts;” Gk. poikilos “multicolored;” L. pingit “embroiders, paints;” O.C.S. pisati “to write;” O.H.G. fēh “multicolored;” Lith. piēšti “to draw, adorn;” PIE base *peik- “colored, speckled.”

Relating to or belonging to a profession.

Etymology (PE): Pišekâr literally “doing as profession,” from pišé, → profession, + kâr “work,” from kar-, kardan “to do, to make,” → -or.

See also: → profession; → -al.

A person who practices astronomy as a profession rather than as a hobby, in contrast to an → amateur astronomer.

See also: → professional; → astronomer.

1. A teacher of the highest academic rank in a college or university.
   

2. An instructor in some art or skilled sport, such as a professor of singing.

Etymology (EN): M.E. from L. professor “one who has taken the vows of a religious order,” agent noun from profitieri “declare openly,” from → pro- “forth” + fateri “to acknowledge, confess.”

Etymology (PE): Ostâd “professor; master; artisan,” from Mid.Pers. ôstât, from Av.
*aibi-stāta-, *auui-stāta- literally “standing on,” i.e. “appointed; agent; head,” from aibi-/auui- “upon, toward, against” (O.Pers. abiy-; cf. Skt. abhi-; Gk. amphi-) + stā- “to stand” (→ opposition).

A graph or drawing that shows the variation of one property (such as intensity),
usually as ordinate, with respect to another property (such as wavelength).
→ line profile.

Etymology (EN): From It. profilo “a drawing in outline,” from profilare “to draw in outline,” from → pro- “forth” + filare “draw out, spin,” from L.L. filare “to spin, draw out a line,” from filum “thread,” cognate with Pers. zeh “cord, string,” → filament.

Etymology (PE): Farâpâl, from farâ-, → pro-, + pâl “thread, string,” probably cognate with L. filum, as above.

A method of analysis in which the observed stellar image profiles or spectral
line profiles are fitted by model profiles in order to study and derive some properties of the object.

See also: → profile; → fitting;
→ method.

The originator of a line of descent; a precursor.

Etymology (EN): M.E., from O.Fr. progeniteur, from L. progenitorem “ancestor,” agent noun from progenitus, p.p. of progignere “beget,” from → pro- “forth” + gignere “to produce, beget,” cognate with Pers. zâdan, as below.

Etymology (PE): Agent noun from zâdan “to bring forth, give birth” (Mid.Pers. zâtan; Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born;” cf. Skt. janati “begets, bears,”
janitár “progenitor, father;” Gk. genetor “progenitor;” L. gignere “to beget,” nasci “to be born,” as above, PIE base *gen- “to give birth, beget”).

A galaxy which is supposed to be at the origin of a specific event, for example a hypothetical galaxy in which globular clusters might have formed.

See also: → progenitor; → galaxy.

A star which is supposed to be at the origin of phenomenon, for example a progenitor neutron star which has given rise to a black hole.

See also: → progenitor; → star.

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.

Etymology (EN): From → pro- “forward” + grade, from L. gradi “to go, step, walk;” → motion.

Etymology (PE): 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.

See also: → prograde motion; → orbit.

A plan or schedule of activities, procedures, etc., to be followed.
Computers: A precise sequence of instructions in a programming language that tells a computer to perform a task.

Etymology (EN): From L.L. programma “proclamation, edict,” from Gk. programma “a written public notice,” from the stem of prographein “to write publicly,” from → pro- “forth” + graphein “to write.”

Etymology (PE): Barnâmé, originally “model, examplar; acount-book,” from bar-

“on; up; upon; in; into; at; forth; with; near; before; according to” (Mid.Pers. abar; O.Pers. upariy “above; over, upon, according to;” Av. upairi “above, over,” upairi.zəma- “located above the earth;” cf. Gk. hyper- “over, above;” L. super-; O.H.G. ubir “over;” PIE base *uper “over”)

• nâmé “letter; book” (Mid.Pers. nâmak “inscription; letter; book,” related to nâm “name;” Mid.Pers. nâm; O.Pers./Av. nâman-; cf. Skt. nama-;
  Gk. onoma, onuma; L. nomen; PIE *nomen-).

Stars for the observation of which telescope time has been awarded.

See also: → program; → star.

A computer expert who carries out → programming.

See also: Agent noun of the verb → program.

The process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs.

Etymology (EN): Verbal noun of → program.

Etymology (PE): Barnâme-sâzi, from barnâmé, → program,

• sâzi verbal noun 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,” sācaya- (causative) “to teach”).

Math.: A succession of numbers or quantities in which there is a constant relation between each member and the one succeeding it. See also → arithmetic progression, → geometric progression, → harmonic progression.

Etymology (EN): From O.Fr. progression, from L. progressionem “a going forward,” from progressus, p.p. of progredi “go forward,” from → pro- “forward” + gradi “to step, walk,” from gradus “step.”

Etymology (PE): Farâyâzi, from farâ-, → pro-, + yâzi, verbal noun of yâzidan “to stretch out the arms; grow up;” Parthian Mid.Pers. y’d “to reach a goal, come to, stretch out;” Av. yat- to reach, take one’s place," yaiiata “places,’ frā-iiatāt “has reached;” cf. Skt. yat- “to be in place, put in place, line up;” PIE base *iet- “to be in place.”

1. (n.) A specific task or planned program of investigation, especially in scholarship.
   

2a) (v.) To propose, contemplate, or plan.

2b) To throw or cause to fall upon a surface or into space, as a ray of light or a shadow.

2c) To cause (a figure or image) to appear, as on a background.

2d) Geometry: To transform the points of one figure into those of another by a correspondence between points.

Etymology (EN): 1) From L. projectum “something thrown forth,” noun use of neuter of projectus, p.p. of projicere “to stretch out, throw forth,” from → pro- “forward” + combining form of jacere (p.p. jactus) “to throw.”
2) From L. projectus, as above.

Etymology (PE): Farâšândan, from farâ- “forward,”
→ pro- + šândan, from ešândan “to eject,” from Hamadâni ešândan “to throw out,” Laki owštan “to throw, to shoot (with bow and arrow);” Lori šane “throwing,” šane kerde “to throw;” Av. ah- “to throw,” present ahya- “throws,” asta- “thrown, shot,” astar- “thrower, shooter;” cf. Khotanese ah- “to throw, shoot,” Skt. as- “to throw, shoot,” ásyati “throws,” ásana- “throw, shot,” asanā- “missile.”

A person who directs a project.

See also: → project; → director.

A person who is responsible for directing and controlling the work and staff of a project.

See also: → project; → manager.

The → angular velocity of a star deduced from the → rotational broadening of its → spectral lines. It is expressed as v sini, where i is the → inclination of the rotational axis with respect to the normal to the → plane of the sky. The real equatorial rotational velocity can be determined only if the inclination of the rotational axis is known.

See also: Projected, p.p. of → project; → rotational; → velocity.

A body projected or impelled forward, as through the air.

Etymology (EN): From Mod.L. projectilis, from L. projectus, p.p. of proicere; → project.

Etymology (PE): Partâbé, from partâb “a throw, an arrow that flies far,” partâbidan “to throw,” from Proto-Iranian *para-tau-, from *para- “forward,” → pro- + *tau- “to throw, spread, sow;” cf. Tabari tâb “throwing,” tâb dəən “to throw;” Chorasmian mftw- “to perish, be destroyed, disturbed;” Ossetic aeftawyn “to throw on; to increase; to pull out.”

1. The act, process, or result of projecting.
   
2. The act of reproducing on a surface, by optical means, a remote image on a film, slide, etc.

See also: Verbal noun of → project.

An apparatus for projecting an image from a film, a slide onto a screen.
A device for projecting a beam of light.

See also: → project + → -or.

Elongated in the direction of the polar diameter; opposed to → oblate

Etymology (EN): From L. prolatus, pt.p. of proferre “to bring forward, extend,”
from → pro- + → oblate.

Etymology (PE): Kešidé p.p. of
Mod./Mid.Pers. kešidan, kašidan “to draw, protract,
trail, drag, carry,” dialectal Yaqnavi xaš “to draw,” Qomi xaš “streak, stria, mark,” Lori kerr “line;”
Av. karš- “to draw; to plow,” karša- “furrow;” Proto-Iranian *kerš-/*xrah- “to draw, plow;” cf. Skt. kars-, kársati “to pull, drag, plow;”
Gk. pelo, pelomai “to move, to bustle;” PIE base k^wels- “to plow.”

An ellipsoid produced by rotating an ellipse through 360° about its major axis. → oblate spheroid.

See also: → prolate; → spheroid.

The third closest satellite of Saturn, also known as Saturn XVI, orbiting at a distance of 139,350 km. It orbits Saturn in 0.613 days and acts as a shepherd moon to Saturn’s F ring beyond it. It is irregularly shaped, 145 x 85 x 62 km. Prometheus was iscovered by S. Collins and others in 1980 from Voyager photos.

See also: In Gk. mythology, Prometheus was a Titan who stole fire from Olympus and gave it to humankind, for which Zeus punished him horribly; son of Iapetus; brother of Atlas and Epimetheus. The name literally means “forethought,” from from promethes “thinking before,” from → pro- “before” + mathein “to learn,” from enlargement of PIE base *men- “to think;” → idea for Pers. cognates.

Artificially produced radioactive chemical element; symbol Pm, the last of the rare-earths family elements to be discovered. Atomic number 61; mass number of most stable isotope 145; melting point 1,042°C; boiling point 3,000°C.

See also: From → Prometheus. The name promethium was preferred to prometheum because most metallic elements have names ending in ium and eum would have caused problems.

A loop of hot, luminous gas in the Sun’s → corona consisting of cool dense → plasma supported by magnetic fields. Prominences appear bright when seen against the cool blackness of space. When they are in silhouette against the disk they are known as → filaments. Their spectrum is dominated by lines of hydrogen, helium, and calcium. Prominences have temperatures of about 10,000 K, typical of the solar → chromosphere, and densities 100 times greater than the corona. There are → quiescent prominences and → active prominences.

Etymology (EN): From L. prominentia “a jutting out, protuberance,” from prominere “jut or stand out,” from → pro- “forward” + minere “to project.”

Etymology (PE): Zabâné “tongue-like” (flame), from zabân “tongue;
→ language,” + suffix -é.

1a) A declaration that something will or will not be done, given, etc., by one.

1b) An express assurance on which expectation is to be based.

2. To engage or undertake by promise; to make a promise (Dictionary.com).

Etymology (EN): M.E. promis(se), from O.Fr. promesse “promise, guarantee, assurance” and directly from L. promissum “a promise,” from promittere “send forth; let go; assure beforehand, promise,” from → pro- + mittere “to release; send.”

Etymology (PE): Fargot, literally “word (say, saying) put forth,” from far-, variant of farâ-, → pro-, + got, from gotan, gutan (as in Kurd. (Kurm.) gôtin, guhtin, (Sor.) gutin, Gilaki gutan, Shahmerzadi. -got- “to speak”), variant of goftan “to say, tell, utter,” Mid.Pers. guftan; O.Pers. gaub- “to say.”

Showing signs of future success (OxfordDictionaries.com).

See also: → promise; → -ing.

1. To further or encourage the progress or existence of.
   

   2. To raise to a higher rank, status, degree, etc.
      

   3. (Education) To advance (a pupil or student) to a higher course, class, etc.
      

   4. To urge the adoption of; work for.
      

   5. (Marketing) To encourage the sale of (a product) by advertising or securing financial support (FreeDictionary.com).

Etymology (EN): M.E. promoten, from O.Fr. promoter and directly from L. promotus, p.p. of promovere</i< “move forward; cause to advance; reveal,” from → pro- “forward” + movere “to → move.”

1. The act of promoting someone to a higher job, grade, or rank, or the fact of being so promoted.
   

   2. Support or encouragement of the progress, growth, or acceptance of something.
      

   3. An act, event, or offer that helps to increase interest in or demand for something (FreeDictionary.com).

Etymology (EN): Verbal noun of → promote.

Etymology (PE): Farkašan, literally “draw forward, pull up,” from far-, variant of farâ-, → pro-, + kašan “drawing, pull,” from kaš present stem of kašidan, → galaxy, + noun suffix -an.

Quick, at once or without delay.

Etymology (EN): M.E., from O.Fr. prompt, from L. promptus “brought forth, ready, quick,” p.p. of promere “to bring forth,” from → pro- “forward” + emere “to take.”

Etymology (PE): Tond, “swift, rapid, brisk; fierce, severe,” Mid.Pers. tund “sharp, violent;” Sogdian tund “violent;” cf. Skt. tod- “to thrust, give a push,” tudáti “he thrusts;” L. tundere “to thrust, to hit” (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere “to thrust or bore through,” from per- + tundere, as explained); PIE base *(s)teud- “to thrust, to beat.”
Biderang “without delay,” from bi- negation prefix, → in-, + derang, → delay.

Neutrons emitted immediately by a nucleus undergoing fission, as opposed to → delayed neutrons, which are emitted by one of the fission products an appreciable time interval after the fission event (from a few milliseconds to a few minutes).

See also: → prompt; → neutron.

A mechanism predicted by theoretical models of → supernova explosion in the case when the → supernova shock breaks through the outer edge of the collapsing → iron core before losing all of its energy (through → photodisintegration of the iron nuclei) and manages to expel the stellar envelope.
Compare with → delayed supernova explosion.

See also: → prompt; → supernova; → explosion. See also → delay.

A grammatical element which replaces a noun previously mentioned.

Etymology (EN): From M.Fr. pronom, from L. pronomen, from → pro- “in place of” + nomen, → name.

Etymology (PE): Farânâm, literally “noun (put) forth (to replace),” from farâ- “forward, along, opposing, facing,” → pro- + nâm, → name.

1. To enunciate or articulate (sounds, words, sentences, etc.).
   

2. To utter or sound in a particular manner in speaking:

See also: → pro-; → announce.

1. The act or result of producing the sounds of speech, including articulation, stress, and intonation, often with reference to some standard of correctness or acceptability.
   

2. An accepted standard of the sound and stress patterns of a syllable, word, phrase, etc.(Dictionary.com).

See also: Verbal noun of → pronounce.

1. A particular piece of evidence that is sufficient to show or helps to establish a fact.
   

2. The establishment of the truth of anything; demonstration.
   

3. Math. Logic: A sequence of statements that establishes the truth of a proposition.

Etymology (EN): M.E. prove, prooff, prof, proufe,
O.Fr. prueve, from L.L. proba “a proof,” a back-formation from L. probare “to prove,” from probus “worthy, good, upright,” from PIE *pro-bhwo- “being in front,” from → pro- + *bhu- “to be;” cf. Pers. budan “to be,” → condition.

Etymology (PE): Ãvin, on the model of Ger. Beweis “proof,” from weisen “to show, point out;” O.E. witan “to see.” âvin “to show, see,”
from intensive prefix â- + vin “to see” (as in a large number of dialects), variant bin, present stem of didan “to see;” Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
cf. Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” Ger. weisen “to show,” as above;
PIE base *weid- “to know, to see.”

Information, ideas, or rumors deliberately spread widely to help or harm a person, group, movement, institution, nation, etc. (Dictionary.com).

Etymology (EN): From N.L. propaganda, short for Congregatio de Propaganda Fide, “congregation for propagating the faith,” a committee of cardinals established in 1622 by Gregory XV to supervise foreign missions, from L. propagare, → propagate.

Etymology (PE): Farâtucân, from prefix farâ-, → pro-,

• tucân from tucidan, → propagate.

1. v.intr.: (of → electromagnetic waves, → compression waves, etc.) To travel through space or a physical → medium.
   

2. v.tr.: To create (an effect) at a distance, as by electromagnetic waves, compression waves, etc., traveling through space or a physical medium.

Etymology (EN): From L. propagatus, p.p. of propagare “multiply plants by layers, spread for sprouting, propagate, enlarge,” from propag(es) “something set out, scion, slip,” from → pro- “forth” + pag base of pangere “to fasten” + es noun suffix + -atus “-ate.”

Etymology (PE): Tucidan, from several dialects: Malayeri “to scatter, disperse; to diffuse;”
Lori tic “scattered, dispersed,” ticene “to scatter, disperse; to diffuse;” Laki tvic “dispersed, scattered;” Aligudarzi tij “scattered, dispersed;” Borujerdi tuc “scatter,” tucessan “to scatter, diffuse,” tucesa “dispersed, scattered, diffused;” probably related to Proto-Ir. θrāš- “to scatter, spread, strew” cf. Yaghnobi côš- “to spread, scatter, sow,” tiráš-, têráš-, tirayš-/tirášta “to fall (down, off); to become ill; to drop;” (+*ui- ?) Ossetic .I. irtasyn/irtæst, D. ærtasun/ærtast “to separate, distinguish; to take away; to choose;”
Sogd. š’š “to scatter, disperse;” šyš- “to be scattered” (Cheung, 2007)

Physics: The act or process of propagating, especially the process by which a disturbance, such as the motion of electromagnetic or sound waves, is transmitted through a medium such as air or water.
Linguistically related notions: → diffusion (پخش);
→ dispersion(پاشش); → scattering (پراکنش); → diffraction (پراش).

See also: Verbal noun of → propagate.

A parameter, denoted k = 2π/λ, that along with the → angular frequency, ω = 2πν, is used to express the equation of → simple harmonic motion, y = cos (ωt - kx + π/2). Same as → wave number.

See also: → propagation; → number.

To drive, or cause to move, forward or onward.

Etymology (EN): From L. propellere “to push forward,” from → pro- “forward” + pellere “to push, drive.”

Etymology (PE): Pišrândan, from
piš “before; in front,” from Mid.Pers. pêš “before, earlier,” O.Pers. paišiya “before; in the presence of” + rândan “to push, drive, cause to go,”
causative of raftan “to go, walk, proceed” (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack”).

A propelling agent. A substance, usually a mixture of fuel and oxidizer, for propelling a rocket.

Etymology (EN): From → propel + suffix -ant.

Etymology (PE): Pišrâné, from pišrândan, → propel.

Belonging or pertaining exclusively or distinctly to a person, thing, or group. → proper mass; → proper motion; → proper time.

Etymology (EN): M.E., from O.Fr. propre, from L. proprius “one’s own.”

Etymology (PE): Saré “pure; principal.”

A distance between two nearby events in the frame in which they occur at the same time. It is the distance measured by a ruler at the time of observation. Hence, for a cosmological time t, D_proper = D_C . a(t), where D_C is the → comoving distance, and a(t) is the → scale factor. In the present epoch a = a(t_obs) = 1, and D_proper = D_C.

See also: → proper; → distance.

Same as → rest mass.

See also: → proper; → mass.

The apparent motion of a star across the sky (not including a star’s parallax), arising from the star’s velocity through space with respect to the Sun. Proper motion is usually tabulated in star catalogs as changes in right ascension and declination per year or century. See also: → proper motion distance.

See also: → proper; → motion.

The distance derived from the → proper motion of an object. If an object has a known → transverse velocity  u, and has an observed angular motion of dθ/dt, then the proper motion distance is defined as: d = u/(dθ/dt).

See also: → proper; → motion; → distance

Of two sets A and B, the set A if it is contained in B (A ⊂ B) but is not equal to B (A ≠ B).

See also: → proper; → subset.

In general relativity, the time as measured on a clock that travels with the observer in the same system. An accelerated clock will measure shorter time intervals between events than a non-accelerated clock between the same events. → twin paradox.

See also: → proper; → time.

1. General: An essential or distinctive attribute or quality of a thing.
   

2. Physics: A quantity, such as length, mass, pressure, temperature, or volume, that relates to the state of a system and can be expressed in numbers obtained from well-defined measurement operations.

Etymology (EN): From M.E. propriete “ownership, something owned, one’s own nature,” from M.Fr. propriété, from L. proprietas
“ownership, property, propriety,” literally “special character,” noun of quality from proprius “one’s own, special.”

Etymology (PE): Dârâk “thing owned,” from dâr present stem of
dâštan “to have, to possess” + -âk (on the model of xorâk, pušâk, kâvâk). The first element dâštan, from Mid.Pers. dâštan, O.Pers./Av. root dar- “to hold, keep back, maintain, keep in mind;” Skt. dhr- “to to hold, keep, preserve,” dharma- “law;”
Gk. thronos “elevated seat, throne;” L. firmus “firm, stable;” Lith. daryti “to make;” PIE *d^her- “to hold, support.”

A circumstellar disk of dense gas and dust surrounding a young newly formed star, a T Tauri star or Herbig star. In particular, an externally ionized protoplanetary disk seen in emission in the Orion Nebula. → silhouette disk.

See also: Contraction of protoplanetarydisk.

Comparative relation between things, sizes, quantities, numbers, parts, etc.
Math.: A statement of the equality of two ratios.

Etymology (EN): M.E. proporcio(u)n, from
O.Fr. proportion, from L. proportio “comparative relation, analogy,” from the phrase pro portione “according to the relation” (of parts to each other), from pro “for” + portio “part, shar.”

Etymology (PE): Barpâreš, from bar- “on; up; upon; in; into; at; forth; with; near; before; according to” (Mid.Pers. abar; O.Pers. upariy “above; over, upon, according to;” Av. upairi “above, over,” upairi.zəma- “located above the earth;” cf. Gk. hyper- “over, above;” L. super-; O.H.G. ubir “over;” PIE base *uper “over”) + pâr “part, portion, piece” (variants pâréparré “portion, segment (of an orange),” pargâlé, “piece, portion; patch;” (dialects Kermâni pariké “portion, half;” Tabari perik “minute quantity, particle;” Lârestâni pakva “patch;” Borujerdi parru “patch”);
Mid.Pers. pârag “piece, part, portion; gift, offering, bribe;” Av. pāra- “debt,” from par- “to remunerate, equalize; to condemn;” PIE *per- “to sell, hand over, distribute; to assigne;”
Gk. peprotai “it has been granted;” L. pars, as above; Skt. purti- “reward;” Hitt. pars-, parsiya- “to break, crumble”) + -eš suffix.

Being in or characterized by proportion.
Math.: Of two quantities, having the same or a constant ratio or relation.

See also: → proportion + → -al.

A device in which an electronic detection system receives pulses that are proportional to the number of ions formed in a gas-filled tube by ionizing radiation.

See also: → proportional; → counter.

Math.: A relationship bewteen two quantities such that if one quantity changes the other changes in the same proportion; denoted as y ∝ x.

See also: → proportional + → -ity.

Math.: A → constant that converts a proportionality into an → equation. Thus the proportionality constant k converts the proportionality y ∝ x into the equation y = kx.

See also: → proportionality + → constant.

To offer or suggest (a matter, subject, case, etc.) for consideration, acceptance, or action (Dictionary.com).

Etymology (EN): M.E., from M.Fr. poposer, from → pro- “forth,” + poser “put, place,” → position.

Etymology (PE): Farâhelidan, from farâ-, → pro-, + helidan, heštan “to place, put” from Mid.Pers. hištan, hilidan “to let, set, leave, abandon,” Parthian Mid.Pers. hyrz; O.Pers. hard- “to send forth,” ava.hard- “to abandon;”
Av. harəz- “to discharge, send out; to filter;” hərəzaiti “releases, shoots;” cf. Skt. srj- “to let go or fly, throw, cast, emit, put forth;” Pali sajati “to let loose, send forth.”

1. The act of offering or suggesting something to be considered, accepted, adopted, or done.
   

2. A plan or scheme proposed.
   

3. Logic: A statement in which something is affirmed or denied, so that it can therefore be significantly characterized as either true or false.
   

4. Math.: A formal statement of either a truth to be demonstrated or an operation to be performed; a theorem or a problem (Dictionary.com).

See also: Verbal noun of → propose.

Logic: Of, relating to, or in the form of a → proposition.

See also: → proposition; → -al.

Logic: A → propositional symbol that represents a → specific → proposition.

See also: → propositional; → constant.

A branch of logic that deals with the → truth values of logical statements (→ sentences, → propositions) and uses → logical connectives to build more complex → expressions. The distinctive feature of propositional logic is that it does not deal with logical relationships and properties that involve the parts of a statement smaller than the simple statements making it up. The propositions are evaluated as → true or → false. A more expressive system is provided by the → first-order logic.

See also: → proposition; → -al; → logic.

An upper case letter, e.g. “A,” “B,” “C,” etc. representing a → proposition. Propositional symbols are divisible into two sorts: → propositional constants and → propositional variables.

See also: → propositional; → symbol.

Logic: A → propositional symbol that represents any
→ proposition whatsoever.

See also: → propositional; → variable.

The act or process of propelling. The state of being propelled.

See also: Verbal noun from → propel.

A colorless, flammable gaseous → hydrocarbon C₃H₆, also known as propene. It is found in coal gas and can be synthesized by cracking petroleum or by the dehydrogenation of propane.

See also: From propyl (prop(ionic acid) + -yl)

• -ene.

A person who institutes or conducts legal proceedings, especially in a criminal court.

Etymology (EN): M.L. prosecutor, agent noun from prosequi “follow after, accompany; chase, pursue;” from → pro- “forward” + sequi “to follow,” → sequence.

Etymology (PE): Dâsetân, literally “justice obtainer,” from dâd,
→ justice, + setân agent noun of setândan “to obtain, to take,” from Mid.Pers. statan “to take, seize;” Av. (+ *fra-) frastan- “to take, convey forward;” Proto-Ir. *staHn- “to take;” cf. L. prae-stināre “to buy, fix a price” (Cheung 2007).

1. The outlook for the future.
   

2. To explore a region for mineral deposits.

Etymology (EN): M.E. prospecte, from L. prospectus “view, outlook,” from prospicere “look out on, look forward,” from → pro- “forward” + specere “look at,” → speculate.

Etymology (PE): Farâgâs, from farâ-, → pro-, + gâs “to look,” → speculate.

1. Of or in the future.
   

2. Likely to be or become or come about.

Etymology (EN): From Fr. prospectif, from M.L. prospectivus, from L. prospect-, from prospicere, → prospect.

Etymology (PE): Adj. from farâgâs, → prospect.

A formal statement that gives details of a forthcoming event.

A printed document describing something (such as attractions or services) to clients or members.

Etymology (EN): From L. prospectus “outlook, view,” → prospect.

Etymology (PE): From farâgâs, → prospect, + nuance suffix -é.

A → radioactive → chemical element which is a malleable, shiny silver-gray metal; symbol Pa. → atomic number 91; → mass number of most stable isotope 231; → melting point greater than 1,600°C; → boiling point 4,026°C; calculated → specific gravity 15.37; → valence +4, +5. Protactinium has 24 → isotopes of which only three are found in nature. The most stable is protactinium-231 (→ half-life about 32,500 years); it is also the most common, being found in nature in all uranium ores in about the same abundance as radium. The element was discovered by Otto Hahn and Lise Meitner, who found one of its isotopes in 1917. It was isolated in 1934, by Aristid von Grosse.

See also: Protactinium, literally “parent of actinium,” because actinium is a decay product of protactinium, from Gk. protos “first,” → proto-,

• → actinium.

Certain frequencies, not used for civil or military purposes (radio, television, communication channels, etc.), which are protected for research in radioastronomy, one such being 21 cm.

Etymology (EN): Protected p.p. of protect, from L. protectus, p.p. of protegere “protect, cover in front,” from → pro- “in front” + tegere “to cover;” → band.

Etymology (PE): Bând, → band; negahdâridé p.p. of negahdâridan, variant of negahdâštan “to keep, behold, preserve, take care of,” from negah, negâh “watch, care, custody, look” + (Mid.Pers. nikâh “look, glance, observation;” Proto-Iranian *ni-kas- “to look down,” from ni- “down” (cf. O.Pers. ni preposition and verbal prefix “down;” Av. nī “down, in ,into;” Skt. ni “down,” nitaram “downward;” Gk. neiothen “from below;” E. nether; O.E. niþera, neoþera “down, downward, below, beneath,” from P.Gmc. *nitheraz (O.S. nithar, O.N. niðr, O.Fris. nither, Du. neder, Ger. nieder); PIE *ni- “down, below”)

• *kas- “to look, appear;” cf. Av. nikā-, nikāta- (in the name of the 15-th nask) “that which is observed,” ākas- “to look;” Mid.Pers. âkâh, Mod.Pers. âgâh “aware, knowing;” Skt. kāś- “to become visible, appear;” Ossetic kast/kaesyn “to look”) + dâridan, dâštan “to have, hold, maintain, possess” (Mid.Pers. dâštan; O.Pers./Av. root dar- “to hold, keep back, maintain, keep in mind;” cf.
  Skt. dhr- “to to hold, keep, preserve,” dharma- “law;” Gk. thronos “elevated seat, throne;” L. firmus “firm, stable;” Lith. daryti “to make;” PIE *dher- “to hold, support”).

1. An expression or declaration of objection, disapproval, or dissent, often in opposition to something a person is powerless to prevent or avoid.
   

2. To give manifest expression to objection or disapproval; remonstrate (Dictionary.com).

Etymology (EN): M.E., from O.Fr. protest, from preotester, and directly from L. protestari “to declare publicly, protest,” from → pro- “forth, before” + testari “testify,” from testis “witness.”

Etymology (PE): Pâxos, literally “strike against,” from pâ-, contraction of pâd- “agianst,” → counter-,

• xos “to strike,” Gazi xos-, xus-, xûs- “to strike, throw;”
  Hamedani xostän, xus- “to throw”, Khunsari xus- “to strike, throw,” Kurd. (Sorani) xa-, (Kurmanji) xistin, xi- “to strike, beat,” Qohrudi xosta “to throw,” Ardestâni xoste, Shughni xust, xay-; Mid.Pers. xwas-, hws- “to trample;” Av. paiti xvanh- “to thresh;”
  Proto-Ir. *huah- “to strike, thresh” (Cheung 2007). ,

1a) (n.) An adherent of any of those Christian bodies that separated from the Church of Rome during the Reformation, or of any group descended from them.

1b) (originally) Any of the German princes who protested against the decision of the Diet of Speyer in 1529, which had denounced the Reformation.

1c) (lowercase) One who makes or enters a protests.

2a) (adj.) Belonging or pertaining to Protestants or their religion.

2b) (lowercase) protesting (Dictionary.com).

Etymology (EN): From Ger. or Fr. protestant, from L. protestantem (nominative protestans), p.p. of protestari, → protest.

Etymology (PE): Pâxosân agent noun or adj. from pâxosidan, → protest.

The religion of → Protestants.

See also: → protestant; → -ism.

1. The act of protesting.
   

2. Formal expression or declaration of objection, dissent, or disapproval (Dictionary.com).

See also: → protest; → -tion.

A person who publicly demonstrates opposition to something. Also protestor.

See also: → protest; → -er.

One of the largest of → Neptune’s known moons discovered in 1989 by the Voyager 2 space probe. Proteus revolves around Neptune at a distance of about 92,800 km, completing one orbit in 26 hours, 54 minutes. Proteus is about 400 m in diameter, larger than → Nereid. Orbiting the planet in the same direction as Neptune rotates, Proteus remains close to Neptune’s equatorial plane. Proteus is irregularly shaped and heavily cratered, but it shows no sign of geological modification. In fact Proteus is about as large as a satellite can be without being pulled into a spherical shape by its own gravity. Proteus is one of the darkest objects in the solar system. Like Saturn’s moon Phoebe, Proteus reflects only six percent of the sunlight that it receives.

See also: Originally designated S/1989 N 1, Proteus is named after the shape-changing sea god of Greek mythology.

The lightest and most common → isotope of → hydrogen, with one → proton and no → neutrons; symbol ¹H. See also → deuterium and → tritium.

See also: From Gk. protos “first” + L. → -ium.

A combining form meaning “first, foremost, earliest form of,” used in the formation of compound words such as → protogalaxy, → protoplanet, → protostar, etc.

Etymology (EN): From Gk. proto-, combining form of protos “first,” superlative of pro “before,” cognate with O.S. pruvu “first;” Rus. pervyy “first;”
Av. pauruua-, as below.

Etymology (PE): Purvâ-, from O.Pers. paruviya- “former, initial,” Av. pourva-, pouruuiia-, pauruua-, paoiriia- “first, initial, former;” cf. Skt. purva- “first, former, being before;” Tokharian B parwe “first;” PIE base *prwos “first.”

The planet Earth during its → protoplanetary stage.

See also: → proto-; → Earth.

The hypothetical but strongly evidenced common ancestor of the Indo-European languages. PIE words are reconstructed from extant Indo-European languages. There is no clear agreement on exactly where or when the speakers of PIE lived. It is believed that most of the subgroups diverged and spread out over much of Europe, Iran, and northern Indian subcontinent during the fourth and third millennia BC. See also → proto-language.

See also: → proto-; + Indo-, → Indus, + → European.

The hypothetical and typically extinct language which is believed to be the ancestor of a group of languages of the same family.
Historical linguistics uses comparative study of the languages of a family to reconstruct the ancestral language even though in most cases it was never recorded. Some examples are → Proto-Indo-European, Proto-Germanic, Proto-Romance, Proto-Sino-Tibetan, etc.

See also: → proto-; → language.

A very huge mass of gas which will give rise to a cluster of galaxies.

See also: → proto-; → cluster.

Computers: A set of rules and methods used for communication and transmission of data between different computer systems. Protocols may be implemented by hardware, software, or a combination of the two. Simple protocols define the behavior of a hardware connection and help with error detection of the bit stream. High level protocols deal with the data formatting, including the syntax of messages, the terminal to computer dialogue, character sets, sequencing of messages etc.

Etymology (EN): M.E. prothogall “draft of a document,” from M.Fr. prothocole, from M.L. protocollum “draft,” literally “the first sheet of a volume” (on which contents were written), from Gk. protokollon “first leaf glued to the rolls of papyrus describing its contents,” from → proto- “first” + kolla “glue.”

Etymology (PE): Purvâband from purvâ-, → proto-, + band “joint; joined,” past stem of bastan “to bind; to shut; to form seed buds; to clot,” from Mid.Pers. bastan/vastan “to bind, shut,” Av./O.Pers. band- “to bind, fetter,” banda- “band, tie;”
Skt. bandh- “to bind, tie, fasten;” PIE *bhendh- “to bind,” cf. Ger. binden, E. bind.

A huge mass of gas that by contraction and condensation becomes a galaxy of stars. A galaxy during the early phase, before it has developed its present shape and stellar/gas content.

See also: → proto-; → galaxy.

A dense disk of liquid and vapor supposed to have formed around the Earth below the Roche limit after the proto-Earth was impacted by a Mars-sized object. The Moon was accreted from the Earth’s mantle material froming the disk. See also → Theia (S. Charnoz and C. Michaut, 2015, arxiv.1507.05658).

See also: → proto-; → lunar; → disk.

A particle of the hadron family which is one of the two particles that make up atomic nuclei. It has an electric charge of one positive fundamental unit,
a diameter of about 1.65 x 10^-13 cm, and a mass of about 1.67 x 10^-24 g
(about 938 MeV c^-2).

See also: From Gk. proton, neuter of protos “first.” Coined by Eng. physicist Ernest Rutherford (1871-1937).

The temperature in the → solar wind, as derived from the mean kinetic energy of protons: mv²/2 = (3/2)kT_p, where k is → Boltzmann’s constant. There are two types of proton temperature: parallel temperature, measured from protons moving parallel to the magnetic field, and perpendicular temperature relating to protons at right angles to the magnetic field. The proton temperature is usually derived using particle detectors on board space probes that determine the velocity → distribution function of the particles from their energies (N. Meyer-Vernet, 2007, Basics of the Solar Wind, Cambridge Univ. Press). See also → electron temperature.

See also: → proton; → temperature.

A series of → thermonuclear reactions,
taking place mainly in → low-mass stars, such as the Sun, which transforms four hydrogen nuclei (protons) into one helium (⁴He) nucleus and thereby generates energy in the stellar core. First, two protons (¹H) combine to form a → deuterium nucleus (²H) with the emission of a → positron (e⁺) and a → neutrino (ν): ¹H + ¹H → ²H + e⁺ + ν. The deuterium nucleus then rapidly captures another proton to form a helium-3 nucleus (³He), while emitting a → gamma ray (γ):
²H + ¹H → ³He + γ. There are three
alternatives for the next step. In the PP I chain, occurring in 86% of the cases, two ³He nuclei fuse to a final ⁴He nucleus while two protons are released: ³He + ³He → ⁴He + ¹H + ¹H. The mass of the resulting ⁴He nucleus is less than the total mass of the four original protons used to produce ⁴He (→ mass defect). The difference, ~ 0.7% of the total mass of the protons, is converted into energy and radiated by the Sun. In this process, the Sun loses some 4 million tons of its mass each second. See also → CNO cycle.

See also: → proton; → chain.

A → thermonuclear reaction in which two protons collide at very high velocities and combine to form a → deuterium. See also → proton-proton chain.

See also: → proton; → reaction.

A compact, hot, and → neutrino-rich object that results from a → supernova explosion and is a transition between an → iron core and a → neutron star or → black hole. The life span of a protoneutron star is less than one minute.

See also: → proto-; → neutron; → star.

A stage in the formation of a → planet, which comes about from the aggregation of → planetesimals. The protoplanet eventually becomes a planet by → accretion of material from a → protoplanetary disk.

See also: → proto- + → planet.

Of or relating to a → protoplanet or protoplanets.

See also: → protoplanet; → -ary.

A → circumstellar disk of gas and dust surrounding a → pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of → accretion disks
which bring forth stars. Typically, their sizes are ~100-500 AU, masses ~10^-2 solar masses, lifetimes ~10⁶-10⁷ years, and accretion rates ~10^-7-10^-8 solar masses per year. According to the standard theory of planet
formation, called core accretion, planets come into being by the growth of → dust grains which stick together and produce ever larger bodies, known as
→ planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the → snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to → Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of → giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a → debris disk around the central object that has become a → main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by → gravitational instabilities.
The validity of these two theories is presently debated. See also → protoplanet.

See also: → protoplanet; → disk.

→ preplanetary nebula.

See also: → proto-; → planetary; → nebula.

The fluid substance within the living cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts.

See also: → proto- + -plasm, → plasma.

Describing the conditions prior to the formation of the → solar system, or pertaining to the → protostar that became the → Sun.

See also: → proto- + → solar.

The abundance of a chemical element pertaining to the proto-→ solar nebula from which the → solar system was formed. → CI chondrite; → CAI meteorite.

See also: → protosolar; → abundance.

A stage in the process of → star formation, after the → gravitational collapse of the dense → pre-stellar core and before the initiation of → nuclear fusion in the central object which will eventually become a star. Protostars are classified into four groups: → Class 0, → Class I, → Class II, and → Class III.

See also: → proto- + → star.

Of or pertaining to → protostars.

See also: → proto-; → stellar.

A → gravitational collapse leading to the formation of a → protostar.

See also: → protostellar; → collapse.

A disk of gas and dust surrounding a → protostar. These structures are rotating → accretion disks through which matter is transferred to protostars.

See also: → protostellar; → disk.

A high-velocity and highly → collimated jet associated with the earliest phase of → star formation that propagating along the polar axis of the → protostar-→ accretion disk system. Protostellar jets are usually detected in the [S II], [O I], and Hα lines and are therefore referred to as optical jets. They may have more than a parsec in length. Their formation is related to the → magnetohydrodynamics (MHD) of accretion disks.

These jets are detected in protostellar sources over a wide range of masses, from the very early stages of formation (sources associated with infalling envelopes whose mass exceeds that of the growing star) all the way to the → classical T Tauri stars, whose envelopes have already dispersed. This phenomenon is thought to play a key role in regulating the star formation process by removing the excess → angular momentum of disk material and enabling matter to flow toward the center.
Protostellar winds also provide an important → feedback mechanism between the forming star and the surrounding medium, to which they return mass and energy. Protostellar jets are at the origin of → bipolar outflows. The et sweeps up ambient → molecular cloud material into two thin shells, which manifest themselves as the observed bipolar lobes of → carbon monoxide (CO) emission. Once the molecular cloud material has been swept away (on a timescale of 10⁵ years), the

bipolar outflow disappears, leaving the protostellar jet to erratically fire away for a further 10⁶-10⁷ years.

See also: → protostellar; → jet.

The Sun at its protostellar formation stage, before becoming a main sequence star, nearly 5 billion years ago.
The protosun was more luminous than today and larger, with a radius comparable to that of the orbits of the inner planets

See also: → proto- + → sun.

The original or model on which something is based or formed.
Something that serves to illustrate the typical qualities of a class.

See also: → proto-; → type.

Capable of being demonstrated or proved.

See also: → prove; → -able.

To supply proof of, to establish or demonstrate the truth or validity of.

See also: → proof.

A short popular saying, usually of unknown and ancient origin, that expresses effectively some commonplace truth or useful thought (Dictionary.com).

See also: → pro-; → verb.

1. The act of provoking.
   

2. Something that → incites,
   → instigates, angers, or irritates (Dictionary.com).

See also: Verbal noun of → provoke.

1. To anger, enrage, exasperate, or vex.
   

2. To stir up, arouse, or call forth (feelings, desires, or activity).
   

3. To → incite or → stimulate (a person, animal, etc.) to action (Dictionary.com).

Etymology (EN): M.E., from O.Fr. provoker, provochier and directly from L. provocare “call forth, challenge,” from → pro- “forth” + vocare “to call,” → voice.

Etymology (PE): Farâvacidan, from farâ-, → pro-, + vacidan “to call,” rarr; convoke.

The forepart of a ship or boat; bow; opposite to stern or poop→ Puppis.

Etymology (EN): From M.Fr. proue, from Upper It. (Genoese) prua, from L. prora “prow,” from Gk. proira, related to pro “before, forward,” → pro-.

Etymology (PE): Farâl, from farâ “forward” (farâ raftan “to go forward, proceed,” farâ rândan “to drive forward”), equivalent to → pro-, + relation suffix -âl, → -al. Compare farâl with prow “bow,” Fr. la proue “prow, bow,” from dialectal It. proa, prua, from L. prora “bow,” from Gk. proira, related to pro “before, forward.”