xatthâ-ye tuham, tânhâ-ye ~
Fr.: raies mélangées
→ Spectral lines intermingled.
Fr.: raie D
One of the pair of yellow lines in emission spectra of neutral sodium (Na I). D1 has a wavelength of 5895.94 Å and D2 is 5889.97 Å. This sodium doublet is one of the strongest absorption features in the spectra of late-type stars.
Labelled D in a sequence of alphabetical letters first used by Joseph von Fraunhofer to designate spectral features in the solar spectrum, → Fraunhofer line.
frozen magnetic field line
xatt-e meydân-e meqnâtisi-ye yax basté, ~ ~ ~ rocidé
Fr.: ligne de champ magnétique gelée
magnetic field line
xatt-e meydân-e meqnâtisi (#)
Fr.: ligne de champ magnétique
An imaginary line used for representing the strength and direction of a magnetic field. Charged particles move freely along magnetic field lines, but are inhibited by the magnetic force from moving across field lines.
open magnetic field line
xatt-e bâz-e meydân-e meqnâtisi-ye
Fr.: ligne ouverte de champ magnétique
In the context of solar physics, a → magnetic field line when it crosses the solar surface only once, i.e., when it goes from surface to infinity. This is the case at a sufficiently large scale in → coronal holes. This is mostly not the case in → active regions.
Fr.: raie permise
An ordinary spectral line emitted by atoms undergoing energy transitions that are allowed by the selection rules of quantum mechanics. → forbidden lines.
xatt-e sorx kibideh
Fr.: raie décalée vers le rouge
A spectral line whose wavelength does not coincide with its theoretical value and is shifted toward longer wavelengths.
Fr.: raie résolue
A → spectral line that is not contaminated by other nearby lines.
Fr.: raie thermalisée
A collisionally excited spectral line formed in high density condition well above the → critical density. At such densities the → excitation temperature is at (or very near) the → kinetic temperature of the gas. At low densities, below the critical density, the excitation temperature will be only slightly above the radiation temperature and the emission line will be practically invisible.
Fr.: raie non identifiée
A spectral line whose origin is not clearly established. → line identification.
xatt-e jahân, jahân-xatt (#)
Fr.: ligne d'univers
In relativity, the path traced out in four-dimensional → space-time that represents a continuous sequence of events relating to a given particle. A point on a world line is called an → event. Any straight world line corresponds to an → inertial motion. Curved world lines represent → accelerated motion. A world line that curves corresponds to an accelerated observer. World lines are shown on space-time diagrams.