An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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pericynthion
  پیراماه   
pirâmâh

Fr.: périlune   

The point in the orbit of a satellite around the Moon closest to the Moon; opposite of → apocynthion.

peri- + Gk. Cynthia "goddess of the Moon;" → Cynthian.

Pirâmâh, from pirâ-, → peri-, + mâhmoon.

perigalacticon
  پیراکهکشان   
pirâkahkešân

Fr.: périgalacticon   

The point in an object's orbit around a galaxy when the object lies closest to the galactic center; opposite of → apogalacticon.

peri- + → galaxy.

perigee full Moon
  پرمانگ ِ پیرازم   
pormâng-e pirâzam

Fr.: pleine lune de périgée   

The → full Moon when our natural satellite is at its closest approach to the Earth. Perigee full Moons are as much as 14% larger and 30% brighter than → apogee full Moons. Also called perigee-syzygy full Moon, super full Moon, and → supermoon. The Supermoon on November 14, 2016, was the closest (356,523 km) a Full Moon has been to Earth since January 26, 1948. The next time a Full Moon is even closer to Earth (356,448 km) will be on November 25, 2034.

perigee; → full; → moon.

perigee-syzygy full Moon
  پرمانگ ِ پیراهور-یوجان   
pormâng-e pirâhur-yujân

Fr.: lune de périgéé-syzygie   

perigee full Moon.

perigee-; → syzygy; → full; → moon.

perihelion
  پیراهور   
pirâhur

Fr.: périhélie   

The nearest point to the Sun in an orbit around the Sun; opposite of → aphelion.

Perihelion, from L. perihelium, from → peri- + helios "sun," cognate with L. sol, Skt. surya, Av. hvar-, Mod.Pers. xor, hur, O.H.G. sunna, Ger. Sonne, E. sun; PIE *sawel- "sun".

Pirâhur, from pirâ-, → peri-, + hur "sun," as above;

perihelion advance
  پیشرفت ِ پیراهور   
pišraft-e pirâhur

Fr.: avance du périhélie   

advance of perihelion.

advance of perihelion.

perihelion distance
  اپست ِ پیراهوری   
apest-e pirâhuri

Fr.: distance au périhélie   

The distance between the → Sun and an → object in orbit around it when they are at their closest approach.

perihelion; → distance.

perihelion precession
  پیشایانِ پیراهوری   
pišâyân-e pirâhuri

Fr.: précession du périhélie   

advance of perihelion.

perihelion; → precession.

period-luminosity relation
  باز‌آنش ِ دوره-تابندگی   
bâzâneš-e dowré-tâbandegi

Fr.: relation période-luminosité   

A → correlation between the periods and luminosities of → Cepheid variable stars: Cepheids with longer periods are intrinsically more luminous than those with shorter periods. The relation was discovered by Henrietta Leavitt in 1912 when studying Cepheids in the → Small Magellanic Cloud. Once the period of a Cepheid variable is determined from observations, the period-luminosity relation can be used to derive its luminosity. Since luminosity is a function of → distance, the distance can then be calculated with the luminosity. The period-luminosity relation is an invaluable tool for the measurements of distances out to the nearest galaxies and thus for studying the structure of our own Galaxy and of the Universe.

period; → luminosity; → relation.

period-mean density relation
  باز‌آنش ِ دوره-چگالی ِ میانگین   
bâzâneš-e dowré-cagâli-ye miyângin

Fr.: relation période-densité moyenne   

A relation that gives a rough estimate of the oscillation period of a → pulsating star as a function of its mean density. This relation is obtained by considering how long it would take a sound wave to travel across the diameter of a model star: Π ≅ (3π/2γGρ)1/2, where ρ is the mean density, γ the ratio of → specific heats (Cp/Cv), and G the → gravitational constant. This relation shows that the pulsation period of a star is inversely proportional to the square root of its mean density. And this is the reason why the pulsation periods decrease along the → instability strip from the luminous, very tenuous → supergiants to the faint, very dense → white dwarfs.

period; → mean; → density; → relation.

periodic function
  کریای ِ دوره‌ای   
karyâ-ye dowreyi

Fr.: fonction périodique   

A function f(x) if for all x, f(x + P) = f(x), where P is a positive constant. The least value of P > 0 is called the period of f(x).

periodic; → function.

periodic motion
  جنبش ِ دوره‌ای   
jonbeš-e dowreyi

Fr.: mouvement périodique   

Any motion that recurs in identical forms at equal intervals of time.

periodic; → motion.

peripheral response
  پاسخ ِ پیرابَری   
pâsox-e pirâbari

Fr.: réponse périphérique   

In a charge-coupled device, the detection of charge collected by the transport register rather than by the image-sensing elements.

peripheral; → response.

peripheral vision
  دید ِ پیرابَری   
did-e pirâbari

Fr.: vision périphérique   

In optics, the ability to see over large angles of view.

peripheral; → vision.

permission
  پرزامش   
parzâmeš

Fr.: permission   

The act of permitting. Authorization granted to do something.

verbal noun of → permit; → -tion.

permitted transition
  گذرش ِ پرزامیده   
gozareš-e parzâmidé

Fr.: transition permise   

A transition between two quantum mechanical states that does not violate the quantum mechanical selection rules.

permitted; → transition.

permutation
  پرموتش، جایگشت   
permuteš, jâygašt

Fr.: permutation   

Math.: A rearrangement of the elements of a set in a particular order. The number of permutations of n objects is equal to n! (→ factorial n). For example, there are 24 permutations of letters A, B, C, and D (4! = 1 × 2 × 3 × 4). The number of permutations of n objects taken r at a time is denoted by nPr and equals n! / (n - r)!. For example, the number of permutation of A, B, C, and D taken two at a time is 12. If n objects are of k different kinds, with r1 alike of one kind, permutations of n objects equals n! / r1! r2! ... rk!, where r1 + r2 + ... rk = n.

Verbal noun of → permute.

Permuteš, verbal noun of → permute.
Jâygašt , from "place" (from Mid.Pers. giyag "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night") + gašt past tense of gaštan, gardidan "to turn, to change" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend").

perpetual motion
  جنبش ِ همیشگی   
jonbeš-e hamišegi

Fr.: mouvement perpétuel   

The motion of a hypothetical machine which, once set in motion, will go on for ever without any losses due to → friction or other forms of → dissipation of energy and without receiving any external energy.

perpetual; → motion.

person
  تنوم   
tanum

Fr.: personne   

1) A human being, whether man, woman, or child as distinguished from an animal or a thing.
2) Philosophy: A self-conscious or rational being.
3) Grammar: Any one of three forms of verbs and pronouns used to denote the speaker, the person addressed, or somebody else being referred to.
4) Law: A living human being or a group, either or both having legal rights and responsibilities.
See also:
personal, → personal equation, → personality.

M.E. persone, from O.Fr. persone "human being," from L. persona "human being," originally "character in a drama, mask," possibly borrowed from Etruscan phersu "mask," from Gk. prosopa "face; mask" + -na a suffix.

Tanum, from O.Pers. and Av., related to Mod./Mid.Pers. tan "body, person," O.Pers. tanūš "body," tanūm [acc.sg.] "(to) onself;" Av. tanū- "body, person, self," tanūm [acc.sg.]; cf. Skt. tanūš- "body, self;" PIE base *ten-uh- "body."

personage
  تنومسا   
tanumsâ

Fr.: personnage   

1) A person of distinction or importance.
2) A dramatic, historical, or fictional → character in a play, story, etc.

M.E. "form, appearance, stature, figure, air, and the like, of a person," from O.Fr. personage "size, stature; a dignitary," from M.L. personagium, from persona, → person.

Tanumsâ, from tanum, → person, + -sâ, contraction of -âsâ, suffix of "form, type, similarity."

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