Fr.: magnitude limite
The faintest magnitude reachable by an instrument.
A widely occurring ore of yellowish-brown to black color that consists of amorphous oxides of iron.
Gk. leimon "meadow" in reference to its occurrence as "bog ore" in meadows and marshes + → -ite.
Fr.: résonance de Lindblad
A kinematic resonance hypothesized to explain the existence of galactic → spiral arms. It occurs when the frequency at which a star encounters the spiral → density wave is a multiple of its → epicyclic frequency. Orbital resonances occur at the location in the disk where Ωp = Ω ± κ/m, where Ωp is → pattern speed, κ → epicyclic frequency, and m an integer representing the number of spiral arms. The minus sign corresponds to the inner Lindblad resonance (ILR) and the plus sign to the outer Lindblad resonance (OLR). The corotation resonance corresponds to Ωp = Ω. In general, the Lindblad resonances are defined for two spiral arms (m = 2), and low order. There are other less important resonances corresponding to higher m values. These resonances tend to increase the object's orbital eccentricity and to cause its longitude of periapse to line up in phase with the perturbing force. Lindblad resonances drive spiral density waves both in galaxies (where stars are subject to forcing by the spiral arms themselves) and in Saturn's rings (where ring particles are subject to forcing by Saturn's moons).
After the originator of the model, Bertil Lindblad (1895-1965), a Swedish astronomer, who made important contributions to the study of the rotation of the Galaxy; → resonance.
xatt (#), xat (#)
1) A mark or stroke long in proportion to its breadth, made with a pen, pencil,
or other tools.
M.E. li(g)ne "cord, rope, stroke, series," from O.E. line "rope, row of letters," partly from O.Fr. ligne, from L. linea "linen thread, string, line," from phrase linea restis "linen cord," from fem. of lineus (adj.) "of linen," from linum "flax, linen."
Xatt, xat, used also in Ar., but it has no Hebrew counterpart. Xat is probably of Iranian origin, from *kerš-/*xrah- "to draw, plow;" cf. Av. karš- "to draw; to plow," karša- "furrow;" Mid/Mod.Pers. kešidan, kašidan "to draw, protract, trail, drag, carry," dialectal Yaqnavi xaš "to draw," Qomi xaš "streak, stria, mark," Lori kerr "line;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base kwels- "to plow."
In stellar atmosphere models, the effect of metallic lines on the atmospheric structure of stars. The additional opacities of thousands of metallic lines alter the radiative transfer, leading to changes in the temperature. The emergent spectrum is consequently modified.
Fr.: confusion de raies
Mixing of two or more spectral lines of adjacent wavelengths into a broad, single line due to insufficient dispersion of the spectrograph.
Fr.: blocage par raies
Reduction of the radiative flux in a model atmosphere due to absorption by a large number of lines. Line blocking affects the radiative transfer, ionisation and temperature structures, and the atmosphere's hydrodynamics.
→ line; block, from M.E. blok "log, stump," from O.Fr. bloc "log, block," via M.Du. bloc "trunk of a tree."
Bandâri "blocking," from band âvardan "to block," from band "dam, tie, chain," from bastan "to bind, shut, close up" (Mid.Pers. bastan, band; Av./O.Pers. band- "to bind, fetter," banda- "band, tie;" cf. Skt. bandh- "to bind, tie, fasten," bandhah "a tying, bandage;" Goth bandi "that which binds;" O.Fr. bande, bende; O.E. bend; M.E. bende; E. band; PIE base *bendh- "to bind") + âvari verbal noun of âvardan "to cause, produce; to bring" (Mid.Pers. âwurtan, âvaritan; Av. ābar- "to bring; to possess," from prefix ā- + Av./O.Pers. bar- "to bear, carry," bareθre "to bear (infinitive)," bareθri "a female that bears (children), a mother;" Mod.Pers. bordan "to carry;" Skt. bharati "he carries;" Gk. pherein; L. fero "to carry").
Fr.: élargissement de raie
A widening of → spectral lines due to any of several factors, including the → Doppler broadening, → instrumental broadening, → microturbulence, → pressure broadening, → rotational broadening, the → Stark effect, and the → Zeeman effect.
Fr.: refroidissement dû aux raies
In stellar atmosphere models, the decrease of temperature in the outer layers of atmosphere due to the escape of photons through optically thin metallic lines. Energy is transferred from the thermal pool to photons and is lost for the atmosphere, leading to a temperature decrease.
Fr.: identification de raies
The process of recognizing the spectral lines in a spectrum.
Fr.: intensité de raie
A measure of the total effect of an absorption or emission line. The line intensity is equal to the integration of the absorption coefficient over the entire shape of the absorption line.
line of action
xatt-e žireš, ~ koneš
Fr.: ligne d'action
Of a force, the straight line along which the force → vector is directed. The action of a force on a → rigid body does not change when its point of application is displaced along the line of action. Hence, forces applied to a rigid body can be regarded as non-localized, or sliding, vectors.
line of apsides
Fr.: ligne des apsides
line of equinoxes
Fr.: ligne des équinoxes
The intersection of the planes of ecliptic and celestial equator.
line of flow
Fr.: ligne d'écoulement
Same as → streamline.
line of force
khatt-e niru (#)
Fr.: ligne de force
One of many → imaginary lines whose direction at all → points along its length is that of the electric or → magnetic field at those points. In → electric fields the lines of force are directed toward → negative charges and point away from → positive charges. In magnetic fields the lines of force are directed from the → north pole to the → south pole.
line of induction
Fr.: ligne d'induction
Same as → line of force in a magnetic field.
line of nodes
xatt-e gerehhâ (#)
Fr.: lignes des nœuds
The line created by the intersection of the equatorial plane and the orbital plane.
line of sight
xatt-e did, didxatt (#)
Fr.: ligne de visée
The imaginary straight line connecting the object and the objective lens of the viewing device.
Fr.: profil de raie
The representation of a spectral line as produced by an observing instrument.