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

Same as → parity symmetry.

→ parity; → symmetry.

→ compressional wave.

P, referring to → pressure; → wave.

A prefix meaning thick.

From Fr. pachy-, from L., from Gk. pachys "thick," akin to Av. bazah "high, deep," Baloci baz "thick, dense," ON bingar "heap," Latvian biezs "dense, thick."

Bazâ-, from Av. bazah, Baloci baz, as above; cf. Waxi bâj "thickness," variant dabz, → concentrated.

The difference between the isotopic mass of a nuclide and its mass number divided by its mass number. The packing fraction is a measure of the stability of the nucleus.

Packing, from the verb pack "to put together in a pack," from the noun pack, from M.E. pak, packe, from M.D. pac or perhaps M.L.G. pak; → fraction.

Barxé, → fraction; anbâštegi quality noun of anbâštan, anbârdan "to fill, to replete;" Mid.Pers. hambāridan "to fill;" from Proto-Iranian *ham-par-, from prefix ham- + par- "to fill;" cf. Av. par- "to fill," parav-, pauru-, pouru- "full, much, many;" O.Pers. paru- "much, many;" Mid.Pers. purr "full;" Mod.Pers. por "full, much, very;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full.

1) Something consisting of or regarded as having two parts or pieces joined together. → pair annihilation; → pair production.
2) Two identical, similar, or corresponding things.

M.E., from O.Fr. paire, from L. paria "equals," neuter plural of par (genitive paris) "a pair, counterpart, equal."

1) Joft "pair, couple," Lori, Laki jeft, Qâyeni jof, Tabari jeft, Mid.Pers. yuxt "pair, couple," Av. yuxta- "a team of horses," from yaog- "to yoke, harness, put to; to join, unite," infinitive yuxta, Mid.Pers. jug, ayoxtan "to join, yoke," Mod.Pers. yuq "yoke;" cf. Skt. yuga- "yoke," Gk. zygon "yoke," zeugnyanai "to join, unite," L. jugare "to join," from jugum "yoke," P.Gmc. *yukam, E. yoke; PIE *yeug- "to join."
Hamâl, from ham- "together, with; same, equally, even" (Mid.Pers. ham-, like L. com- and Gk. syn- with neither of which it is cognate. O.Pers./Av. ham-, Skt. sam-; also O.Pers./Av. hama- "one and the same;" Skt. sama-; Gk. homos-; originally identical with PIE numeral *sam- "one," from *som-. The Av. ham- appears in various forms: han- (before gutturals, palatals, dentals) and also hem-, hen-) + suffix -âl, → -al.

Mutual destruction of a particle and its antiparticle, such as an electron-positron pair, when they collide. The total energy of the two particles is converted into energy as gamma rays. It is the inverse process to → pair production.

→ pair; → annihilation

An instability arising from the → pair production inside a → massive star leading to energetic → supernova explosions. The pair instability occurs when, late in the star's life, the core reaches a sufficiently high temperature after → carbon burning, a condition in which the pair production can take place. The pairs of electron and positron annihilate to form a neutrino and an anti-neutrino. Consequently, the pressure drops and the outer layers fall in onto the core. The temperature and pressure increase rapidly and eventually titanic nuclear burning causes an extraordinary explosion with energies higher than 10⁵¹ erg. See also → pair-instability supernova and → pulsational pair-instability supernova.

→ pair; → instability.

The creation of an → elementary particle and its → antiparticle from a → boson. For example, the formation of an → electron and a → positron in the interaction of high-energy → gamma ray photons, having at least 1.02 Mev, with an → atomic nucleus (γ → e^- + e⁺). The → rest masses of the electron and positron being 0.51 MeV each, the excess energy will be carried away by these two particles. Pair production is the inverse process to → pair annihilation.

→ pair; → production

→ pair instability

→ pair; → instability.

A special type of → supernova that would result from the → pair instability in → supermassive stars with a mass range between 140 and 260 Msun in a low → metallicity environment. Such objects descended from the → Population III stars in the early history of the Universe. Such supernovae are the most powerful thermonuclear explosions in the Universe. Pair-instability supernovae may have played an important role in the synthesis of → heavy elements. Moreover, the energetic feedback of the processed elements to their surroundings could have affected the structure and evolution of the early Universe (See, e.g., Fryer et al. 2001, ApJ 550, 372; Heger & Woosley 2002, ApJ 567, 532). See also → pulsational pair-instability supernova.

→ pair; → instability; → supernova.

In nuclear physics, the extra binding energy associated with pairs of nucleons of the same kind. This quantity expresses the fact that nuclei with odd numbers of neutrons and protons have less energy and are less stable than those with even numbers of neutrons and protons.

Pairing, verbal noun of → pair; → energy.

The roof of the → mouth, separating the oral and nasal cavities. → hard palate; → soft palate.

M.E., from O.Fr. palat and directly from L. palatum "roof of the mouth."

Kâm "roof of the mouth," of unknown origin.

Lacking in color, not bright, weak in color or shade.

M.E., from O.Fr. paile "pale, light-colored," from L. pallidus "pale, pallid, colorless," from pallere "be pale, grow pale."

Pâl, from p(ox) + âl, a combination of (Delijân) pox "pale" + (Kurd) âl "pale."

A prefix meaning "old, ancient" especially in reference to former geologic time periods, e.g. → paleoclimatology, → paleolithic, and → paleomagnetism.

From Gk. palaio-, combining form of palaios "old, ancient," from palai "long ago, far back," from PIE root *kwel- "to turn, move about," also "far"

Pârin, pâriné "ancient," also "last year" (contraction of pâr sâl), related to pir "old;" Mid.Pers. pir "old, aged, ancient;" Av. parô (adv.) "before, before (of time), in front (of space);" cf. Skt. puáh, combining form of puras "before (of time and place), in front, in advance."
Dirin, diriné "old, ancient, of times past," from dir "old, antique; a long while" + suffix -in. The first component from Mid.Pers. dêr, variants dagr, drâz "long" (Mod.Pers. derâz "long," variant Laki, Kurdi derež); O.Pers. darga- "long;" Av. darəga-, darəγa- "long," drājištəm "longest;" cf. Skt. dirghá- "long (in space and time);" L. longus "long;" Gk. dolikhos "elongated;" O.H.G., Ger. lang; Goth. laggs "long;" PIE base *dlonghos- "long." The second component -in adj. suffix, from Mid.Pers. -ên (as in âhênên, zarrên), from Av. -aēna- (ayanhaēna- "made of iron," zaranaēna- "golden"); cf. Skt. -ēna-.

The climate during a past geologic time or before historical records.

→ paleo-; → climate.

The study of past → climates throughout → geologic and → historic time (paleoclimates), and the causes of their variations.

→ paleo-; → climatology.

A period of → geologic time lasting about 42 million years, roughly from 65 to 23 million years ago. The Paleogene is most notable as being the time in which mammals evolved from relatively small, simple forms into a large group of diverse animals in the wake of the → Cretaceous-Paleogene extinction event that ended the preceding → Cretaceous period. Birds also evolved considerably during this period, changing into roughly modern forms.

Literally "ancient birth," from → paleo- + -gene, → gene.

Of, pertaining to, or characteristic of the cultures of the Old Stone Age, marked by the earliest known chipped stone tools. The period continued from about 750,000 years ago, until the beginning of the Mesolithic Age, about 15,000 years ago.

→ paleo-; lithic, from Gk. lithos "stone."

The study of natural remanent magnetization in order to determine the intensity and direction of the Earth's magnetic field in the geologic past.

→ paleo-; → magnetism.

The study of ancient life through → fossils.

From Fr. paléontologie, from paléo-, → paleo-, + onto-, from Gk. ont- "being," pr.p. of einai "to be," + → -logy.

Pârin-šenâsi, from pârin-, → paleo- + šenâsi, → -logy.