Fr.: rayon isophotal
The size attributed to a galaxy corresponding to a particular level of → surface brightness. The reason is that galaxies do not have sharp edges.
A line joining points with the same surface brightness on a plot or in image of a celestial object such as a nebula or galaxy.
Isophote, from → iso- + a combining form of Gk. phos (gen. photos) "light."
Izošid, from izo-, → iso-, + šid "light, sunlight," from Mid.Pers. šêt "shining, radiant, bright;" Av. xšaēta- "shining, brilliant, splendid, excellent."
The quality of an imaging system which is characterized by → isoplanatism.
Izobirâh, from izo-, → iso-, + birâh "a devious path; a wanderer, who deviates, errs."
Fr.: angle isoplanatique
The angle in which the → point spread function of the atmosphere/telescope system is space invariant. Because of the presence of → turbulence in high layers of the atmosphere, this angle is extremely small, often only a few seconds of arc at visible wavelengths. See also → aplanatism.
pac-e izobirâh, teke-ye ~
Fr.: tache isoplanatique
The spatial region where the variation of the → point spread function of an imaging system is considered negligible.
In an imaging system, the unvarying of the → point spread function over an extended field of view.
The condition in which the wavefronts arriving from different parts of a region of sky undergo almost identical phase perturbations. See also → isoplanatic patch.
A line on a map connecting points of equal value. For example the contour lines joining points of equal altitude on a topographic map. Some other examples of isopleths are: → isobar, → isoneph, and → isohel.
Izocand, from izo-, → iso-, + cand replacing candi (after prefix) "quantity," from Mid.Pers. candih "amount, quantity," from cand "how many, how much; so many, much;" O.Pers. yāvā "as long as;" Av. yauuant- [adj.] "how great?, how much?, how many?," yauuat [adv.] "as much as, as far as;" cf. Skt. yāvant- "how big, how much;" Gk. heos "as long as, until."
sebar-e do-pahlu-barâbar (#)
Fr.: triangle équilatéral
A triangle having two sides equal.
From L.L. isosceles, from Gk. isoskeles "with equal legs; that can be divided into two equal parts," from isos "equal, identical," → iso-, + skelos "leg."
A quantum number based on the assumption that the nucleon (proton and neutron) is a single entity having two states, like → spin. It is conserved by the strong interaction. Same as isotopic spin, isobaric spin.
Meteo.: A line on a map or graph joining points of equal temperature.
Isotherm, back formation from → isothermal.
1) Relating to or having a constant temperature.
Isothermal, from → iso- + therm, from Gk. therme "heat" thermos "warm;" cognate with Pers. garm "warm" (garmâ "heat, warmth," from Mid.Pers. garmâg; O.Pers./Av. garəma- "hot, warm;" cf. Skt. gharmah "heat;" L. formus "warm," fornax "oven;" P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- "warm") + → -al; → process.
Fr.: processus isotherme
A → thermodynamic process that takes place at → constant → temperature. For the temperature of a system to remain strictly constant, the changes in other coordinates (pressure and volume) must be carried out slowly, and → heat must enter or leave the system to maintain a constant temperature. → polytropic process. Astrophysical examples include the → collapse of a → protostar down the → Hayashi track, and the collapse of a star at the end of its life to become a → white dwarf.
Fr.: vent isotherme
A → stellar wind in which the gas is subject to only two forces: the inward directed gravity and the outward directed gradient of the gas pressure.
One of several nuclides having the same number of neutrons in their nuclei but differing in the number of protons.
Isotone, from → iso- + tone, from Gk tonos "strain, tone, mode," literally, "a stretching," akin to teinein "to stretch," cognate with Pers. tanidan "to spin, twist, weave" (Mid.Pers. tanitan; Av. tan- "to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti "stretches," tantram "loom;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch; PIE base *ten- "to stretch;" Pers. târ "string," tân "thread," tur "fishing net, net, snare," and tâl "thread" (Borujerdi dialect) belong to this family; variants tanta "cobweb," tanadu, tafen, kartané, kârtané, kâtené, Pashtu tanistah "cobweb;" cf. Skt. tantu- "cobweb, thread, string").
izotop (#), hamjâ (#)
One of two or more atoms having the same number of protons in its nucleus, but a different number of neutrons and, therefore, a different mass.
Isotope, from → iso- + -tope, from Gk. topos "place."
Izotop, loan from Fr., as above. hamjâ, from ham- "together" → com- + 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").
Fr.: fractionnement isotopique
A slight difference between the → abundances of → isotopes of the same → chemical element owing to → physical or → chemical → processes. It results in the → enrichment or → depletion of an isotope. Same as → isotopic fractionation.
Fr.: décalage isotopique
A displacement in the spectral lines due to the different isotopes of an element.
Of or relating to an → isotope.
Fr.: fractionnement isotopique
Same as → isotope fractionation.