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

A → reversible flow in which the value of → entropy remains → constant; i.e. no energy is added to the flow, and no energy losses occur due to friction or dissipative effects.

→ isentropic; → flow.

A → thermodynamic process for which there is no → heat transfer with the surroundings, and no change in → entropy.

→ isentropic; → process.

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.

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.

A tract of land completely surrounded by water, and not large enough to be called a → continent (Dictionary.com).

M.E. iland, from O.E. igland "island," from ieg "island;" PIE *akwa- "water," cf. Pers. âb, → water, + → land.

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.
Âbxost, ultimately from āpxvasta-, literally "stricken/pounded by water," from *āp-, → water, + *xvasta-, from Proto-Ir. *huah- "to strike, to thresh;" cf. Av. (paiti)xv^anh- "to thresh;" Mid.Pers. xwastan "to tread, trample, thresh;" Mod.Pers. xvast "trampled, beaten," âbxun "island," šabixun "night attack;" Kurd. xistin, xin-, xa- "to strike, to beat;" Hamedâni xostan/xus-, Esfahâni xosan "to throw."
Jaziré loan from Ar. jazirah.
Tomb "island" in Iranian Hormozgâni dialects.

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.

The term "island Universe" was first introduced by the German Alexander von Humboldt in 1850; → island; → Universe.

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-.

1) Meteo.: A line connecting points having equal pressure.
2) Any of a group of nuclides which, although having different atomic numbers, have identical mass numbers; e.g. the tin isotope ¹¹⁵₅₀Sn and the indium isotope ¹¹⁵₄₉In.

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").

A process taking place at constant pressure. → polytropic process.

Isobaric, adj. of → isobar; → process.

Same as → isospin.

Isobaric, adj. of → isobar; → spin.

A process in which the volume remains unchanged.

From → iso- + chor-, from Gk. chora "place, land" + → ic.

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."

Izozamân, from → iso- + zamân→ time.

Having similar angles.

→ iso- + -gonal, → diagonal

Math.: A curve which intersects every member of a given one-parameter family of curves at one and the same angle.

→ isogonal; → trajectory.

Line joining geographical points of equal insolation during a specific interval of time.

From Gk. → iso- + hel, from helios "sun," → helio-.

Izohur, from izo-, → iso-, + hur "sun," cognate with → helio-.

Adaptive optics: The angle over which wavefront phases become de-correlated by 1 radian rms due to → tip-tilt alone. It is defined analogously to the → isoplanatic angle.

→ iso-; → kinetic; → angle.

To set or place apart; detach or separate so as to be alone.
Chemistry: To obtain a substance in an uncombined or pure state.
Physics: → isolated system.

Isolate, back-formation from isolated, from Fr. isolé "isolated," from It. isolato, from L. insulatus "made into an island," from insula "island;" maybe from *en-salos "in the sea," from salum "sea."

Vâyutidan, from vâ- denoting "separation" (also "reversal, opposition; repetition; back, backward," variant of bâz-, from Mid.Pers. abâz-, apâc-; O.Pers. apa- [pref.] "away, from;" Av. apa- [pref.] "away, from," apaš [adv.] "toward the back;" cf. Skt. ápāñc "situated behind") + Mid.Pers. yut "separate, different," Mod.Pers. jodâ "separate, apart;" Av. yuta- "separate, apart" + -idan infinitive suffix.

Set apart or separated from others or other things.

Past participle of → isolate.

A galaxy that is not a member of a dense aggregate. In other words, a galaxy that is formed in a low galactic density environment and has evolved without major interactions with other galaxies of similar mass.

→ isolated; → galaxy.

Massive star formation outside → OB associations. Recent observational findings suggest that → massive star formation is a collective process. In other words, massive stars form in → cluster environments and the mass of the most massive star in a cluster is correlated with the mass of the cluster itself. Nevertheless, other observational results give grounds for supposing that massive stars do not necessarily form in clusters but that they can be formed as isolated stars or in very small groups. According to statistical studies nearly 95% of Galactic → O star population is located in clusters or OB associations. This means that a small percentage, about 5%, of high mass stars may form in isolation. Isolation is meant not traceable to an origin in an OB association. This definition therefore excludes → runaway massive stars, which are thought to result from either dynamical interaction in massive dense clusters, or via a kick from a → supernova explosion in a → binary system. Alternatively, isolated massive star has been defined as follows: An O-type star belonging to a cluster whose total mass is < 100 Msun and moreover is devoid of → B stars (Selier et al. 2011, A&A 529, A40 and references therein).

→ isolated; → massive star; → formation.