Fr.: nombre irrationnel
A → real number which cannot be exactly expressed as a ratio a/b of two integers. Irrational numbers have decimal expansions that neither terminate nor become periodic. Every → transcendental number is irrational. The most famous irrational number is √ 2.
1) bisâmân (#); 2) nârazan-mand
From O.Fr. irregulier, from M.L. irregularis, from → in- "not" + L. regularis from regula "rule," from PIE *reg- "move in a straight line," hence, "to direct, rule" (cf. Pers. râst "right, straight;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right).
Bisâmân, from bi- "not, without" + sâmân "order, arrangement, disposition; boundary, limit," Lârestâni sâmon "sign or mark separating one field from another," Gilaki, Tabari šalmân "a straight peace of wood or beam, post;" Mid.Pers. sâmânak, sahmân "limit;" loaned into Arm. sahmân; cf. Skt. sīmān-, sīmā- "boundary, border, limit."
Fr.: galaxie irrégulière
A galaxy with no spiral structure and no symmetric shape. Irregular galaxies are usually filamentary or very clumpy in shape and tend to smaller than others. Two types of irregular galaxies are defined, → Irr I galaxy and → Irr II galaxy.
bandevâr-e bisâmân, mâh-e ~
Fr.: satellite irrégulier
A satellite whose orbit around its planet is eccentric, inclined with respect to the equatorial plane, and relatively far from the planet. Strong solar perturbations cause the orbit to precess. → regular satellite.
Fr.: variable irrégulière
A type of variable star in which variations in brightness show no regular periodicity. There are two main types, irregular eruptive variables and irregular pulsating variables.
Not capable of returning to an original condition. → irreversible process.
farâravand-e vâgaštnâpazir (#)
Fr.: processus irréversible
A physical process in which the combined → entropy of the → system and the → environment increases. During an irreversible process the system is not in equilibrium at all instances of time. Most of the processes in nature are irreversible. → reversible process.
Having a constant entropy.
Fr.: écoulement isentrope
Fr.: process isentrope
axtaršenâsi-e eslâmi (#)
Fr.: astronomie islamique
The astronomical activities that took place from the 8th to the 14th century in the Middle East, Central Asia, North Africa, and Moorish Spain. The term Islamic should refer to a civilization rather than a religion, because much of the astronomy was secular. In fact more than 90% of "Islamic" astronomy deals with the Greek astronomy → Ptolemaic system, which has obviously nothing to do with religion. Moreover, many non-Muslims within that civilization contributed to this science and must be acknowledged. Apart from these considerations, the term "Islamic astronomy" creates a conceptual disparity. In comparison, the works of European astronomers, such as Copernicus, Galileo, Newton, and others are not placed under "Christian astronomy," and they are indeed not called "Christian scientists." See also → Arabic astronomy, → Islamic calendar.
From Islam, literally "submission" (to God); → astronomy.
gâhšomâr-e eslâmi (#)
Fr.: calendrier islamique
A religious and strictly → lunar calendar which follows the visibility of the lunar crescent after → conjunction and ignores the seasons (see also → synodic month). The year, which consists of 12 months of 29 or 30 days, is approximately 354 days long (→ lunar year of 354.3672 days). Because the calendar follows a purely lunar cycle, each month begins 10 or 11 days earlier each year in relation to the 365-day → solar year. As a result, the cycle of 12 lunar months regresses through the seasons over a period of 33 years. For religious purposes, Muslims begin the months with the first visibility of the lunar crescent. The month length may be 30 or 29 days during four or three successive months respectively. However, astronomers consider a calendar with months of alternately 30 and 29 days. The 33-year period contains 11 → leap years of 355 days. The origin of the Islamic era is considered to be the migration (Hijra) of Prophet Muhammad from Mecca to Medina on 16 July, A.D. 622. It was Caliph Umar (died 644) who, 17 years after the actual event, poised the migration as the beginning of the Muslim era.
From Islam, literally "submission" (to God); → calendar.
âdâk (#), âbxost (#), jaziré (#), tomb (#)
A tract of land completely surrounded by water, and not large enough to be called a → continent (Dictionary.com).
Âdâk, âdak, adak "island" (Dehxodâ), probably from Proto-Ir. *āpdaka-
"placed in water," from *âp-, → water, cf. Pers. âb,
+ *da- "to place, put," cf. Pers. dâdan "to give,"
→ thesis, + suffix *-ka.
The hypothesis first put forward by Immanuel Kant (1724-1804) according to which the objects termed "spiral nebulae" were stellar systems comparable to our own → Milky Way galaxy. At the end of the 18th century, William Herschel (1738-1822) using his giant reflectors discovered thousands of such nebulae. However, in spite of advances in observations it was never possible to prove Kant's idea until the second decade of the twentieth century. The observations using the Mount Wilson 2.50m (100 inch) telescope allowed Edwin Hubble in 1924 to firmly establish that the "spiral nebulae" were unquestionably extragalactic.
izo- (#), ham- (#)
Prefix denoting "equal; homogeneous; uniform." Also is- sometimes before a vowel.
From L.L., from Gk. isos "equal."
Izo-, loan from Gk. isos, as above. The Pers. ham-→ com- is overused; therefore this dictionary adopts izo-.
izobâr (#), izofešâr
1) Meteo.: A line connecting points having equal pressure.
From Gk. isobares "of equal weight," from → iso- + bar, from baros "weight," cognate with Pers. bâr "charge, weight" (Mid.Pers. bâr, from O.Pers./Av. bar- "to bear, carry," Mod.Pers. bordan "to carry;" L. brutus "heavy, dull, stupid, brutish;" Skt. bhara- "burden, load," bharati "he carries;" Mod.Pers. gerân "heavy;" Skt. guru; L. gravis; PIE *gwere- "heavy;" *bher- "to carry, give birth").
Fr.: processus isobare
A process taking place at constant pressure. → polytropic process.
Fr.: spin isobarique
Same as → isospin.
Fr.: processus isochore
A process in which the volume remains unchanged.
Farâravand, → process; izogonj, from izo→ iso- + gonj "volume," gonjdan "to be contained; to hold exactly; to be filled;" Mid.Pers. winj- "to be contained;" Proto-Iranian *uiac-/*uic-; cf. Skt. vyac- "to contain, encompass," vyás- "extent, content, extension;" L. uincire "to bind."
A curve on a → Hertzsprung-Russell diagram connecting all stars having the same age.
Isochrone, back formation from isochronal, from Gk. → iso- + khronos "time."