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

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 ⁿP_r 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! ... r_k!, where r₁ + r₂ + ... r_k = n.

Verbal noun of → permute.

Permuteš, verbal noun of → permute.
Jâygašt , from jâ "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").

M.E., from L. permutare "to change throughout," from per- "through" + mutare "to change," from PIE base *mei- "to change, go, move;" cf. Av. miθô "inverted, false," miθaoxta- "wrong spoken;" Skt. methati "changes, alternates, joins, meets," mith- "to alternate, meet," mithás "opposite, in opposition;" L. meare "to go, pass," mutuus "done in exchange;" Goth. maidjan "to change;" E. prefix mis- (in mistake).

Permutidan, from permute, as above.

A line or plane at right angles to another line or plane. Two curves are said to be perpendicular if their tangent lines are mutually perpendicular. → normal; → vertical

From M.E. perpendiculer(e), from O.Fr. perpendiculiere, from L. perpendicularis "vertical, as a plumb line," from perpendiculum "plumb line," from perpendere "balance carefully," from per- "thoroughly" + pendere "to weigh, to hang."

Pâlâr "pillar, column, main beam."

The → moment of inertia of a plane object (→ lamina) about an axis perpendicular to the plane is equal to the sum of the moments of inertia about any two perpendicular axes in the plane. Thus if x and y axes are in the plane, I_z = I_x + I_y.

→ perpendicular; → axis; → theorem.

Lasting an indefinitely long time; eternal; permanent. → perpetual motion; → perpetual calendar.

M.E. perpetuall, from O.Fr. perpetuel, from L. perpetualis "permanent," from perpetuus "continuous, universal," from perpetis, genitive of Old L. perpes "lasting;"

Hamišegi from hamišé "always;" Mid.Pers. hamišag, from anôšag "immortal," from Av. an-aoša-, from negation prefix → an- + aošah- "death; ruin; corruption" (Mid.Pers. hôš "death;" Mod.Pers. hôš, huš "death; mind; intellect"); cf. derivatives Sogd. nôšé "immortal," nôšak "always;" Mod.Pers. nôš, nuš "the water of immortality; sweet; honey."

A chart or mechanical device that indicates the day of the week for any given date over a period of many years.

→ perpetual; → calendar.

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.

A → meteor shower, one of the three most active of the year, which occurs between July 25 and August 20 with the greatest activity between August 8 and 14, peaking about August 12. The Perseids appear as the Earth's orbit around the → Sun crosses the dusty tail of the comet → Swift-Tuttle, as first explained by Giovanni Schiaparelli (1835-1910), an Italian astronomer. Usually about 50 meteors can be seen per hour, but in outburst years (such as in 2016) the rate can be between 150-200 meteors an hour.

→ Perseus + -ids.

The Hero. A rich constellation in the northern hemisphere between → Auriga and → Cassiopeia, at 3h 20m right ascension, 45° north declination. Beta (β) Persei, or → Algol, is a famous → eclipsing binary star. Abbreviation: Per; genitive: Persei.

The most celebrated of the Greek heroes, the son of Zeus and Danae, who slew the Gorgon Medusa, and afterward saved Andromeda from a sea monster.

Perseus, from Gk., as above, instead of the Arabicized form Barsâvuš (برساووش).

A → radio source in the constellation → Perseus, identified with the supergiant elliptical galaxy → NGC 1275.

→ Persus.

One of the spiral arms of the Galaxy. It is about 5000 light-years farther from the center than the local Orion Arm, in which the Sun lies.

→ Persus; → arm.

A → galaxy cluster of about 12,000 members about 250 million → light-years (→ redshift z = 0.0176) away, covering 4° of sky in the constellation → Perseus. It is dominated by elliptical galaxies. At its center lies the → radio source→ Perseus A. Also known as Abell 426 (→ Abell catalog).

→ Perseus; → cluster.

A long, dense chain of galaxies with a length of almost 300 million → light-years, constituting one of the largest known structures in the → Universe. At the left end of the supercluster lies the massive → Perseus cluster (A426), one of the most massive clusters of galaxies within 500 million light-years.

→ Perseus; → Pisces; → cluster.

Same as → Iranian calendar.

Persian, adj. of Persia, from O.Pers. Pārsa.

Irâni adj. of Irân, from Mid.Pers. Êrân "(land of) the Aryans," pluriel of êr "noble, hero," êrîh "nobility, good conduct;" Parthian Mid.Pers. aryân; O.Pers. ariya- "Aryan;" Av. airya- "Aryan;" cf. Skt. ārya- "noble, honorable, respectable."

1) To continue steadfastly or firmly in some state, purpose, course of action, or the like, especially in spite of opposition, remonstrance, etc.
2) To last or endure tenaciously (Dictionary.com).

M.Fr. persister, from L. persistere "abide, continue steadfastly," from → per- "thoroughly" + sistere "come to stand, cause to stand still," → resist.

Paristâdan from par-, → per-, + istâdan "to stand," → resist.

The act or fact of persisting; the quality of being persistent.

Verbal noun from → persist.

Persisting, especially in spite of opposition, obstacles, discouragement, etc.; persevering (Dictionary.com).

Adjective from → persist.

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."

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."

Of or pertaining to a particular person; individual; private. → personal equation.

→ person; → -al.