پاشش ِ زاویهای pâšeš-e zâvie-yi
*Fr.: dispersion angulaire*
The rate of change of the angles of emergence θ of various
wavelengths from a dispersing prism: dθ/dλ. → *angular*; → *dispersion*. |

پاشش ِ ناسان pâšeš-e nâsân
*Fr.: dispesrion anormale*
The phenomenon whereby the → *refractive index*
of light in a medium changes rapidly with wavelength in the vicinity of
an → *absorption band*.
Hence the → *dispersion curve*
of the substance shows marked deviations from
→ *Cauchy's equation*, in contrast with the behavior of
→ *normal dispersion*.
On the shorter λ side of the absorption band the refractive
index falls off more rapidly than required by Cauchy's equation representing
values of *n* for visible light. On the long λ side of the absorption band
the index is very high, decreasing at first rapidly and then more slowly as one goes beyond
the absorption band. → *anomalous*; → *dispersion*. |

پاشش ِ جوی pâšeš-e javvi
*Fr.: dispersion atmosphérique*
The splitting of starlight into a spectrum in the atmosphere
because the atmosphere acts as a refracting prism. This phenomenon brings about
a practical problem for spectroscopic observations using a slit.
→ *differential refraction*;
→ *atmospheric refraction*. → *atmospheric*; → *dispersion*. |

پاشش چلیپایی، ~ خاجی pâšeš-e calipâyi, ~ xâji
*Fr.: dispersion croisée*
Dispersion of a light beam by using two dispersing elements (grating, grism), one
for separating spectral orders, the other for resolving spectral features within
an order. → *cross*; → *dispersion*. |

پاشش pâšeš (#)
*Fr.: dispersion*
1) The resolution of white light into its component wavelengths,
either by → *refraction* or by → *diffraction*.
Dispersion is actually an effect in which radiations having → *different*
wavelengths travel at different speeds in the medium. Since
the → *angle of refraction*
of each radiation vary as a function of
its → *wavelength*, the component waves deviate from each other.
2) The rate of change of → *refractive index*
with wavelength: *dn*/dλ. → *Cauchy's equation*
shows that dispersion varies approximately as the inverse cube of the wavelength.
3) The selective → *retardation* of → *radio wave*s
when they propagate
through a → *plasma*. As a result, higher
→ *frequency* waves
from a → *pulsar* will arrive at the Earth before the lower
frequencies due to the presence of → *intervening* → *ionized gas*
in the → *interstellar medium*.
→ *dispersion measure*.
4) *Statistics*: The spread of values of a → *variable*
around the → *mean* or → *median*
of a → *distribution*. Verbal noun of → *disperse*. |

خم ِ پاشش xam-e pâšeš
*Fr.: courbe de dispersion*
A graph displaying the variation of the → *refractive index*
of a substance against the wavelength of the electromagnetic wave passing through the
substance. → *dispersion*; → *curve*. |

هموگش ِ پاشش hamugeš-e pâšeš
*Fr.: équation de dispersion*
An equation representing the variation of → *refractive index*
as a function of → *wavelength*; for example
→ *Cauchy's equation* and
→ *Sellmeier's equation*. → *dispersion*; → *equation*. |

اندازهی ِ پاشش andâze-ye pâšeš
*Fr.: mesure de dispersion *
A parameter used in radio astronomy which describes the amount of
dispersion in a radio signal due to its passage through an intervening
plasma. It is proportional to the product of the
interstellar electron density and the distance to the source. → *dispersion*; → *measure*. |

بازانش ِ پاشش bâzâneš-e pâšeš
*Fr.: relation de dispersion*
An equation that describes how the → *angular frequency*,
ω, of a wave depends on its → *wave number*,
*k*. For the simplest of waves, where the speed of propagation, *c*,
is a constant, *ω(k) = ck*.
If the → *phase velocity* depends on *k*, that is for a
dispersive medium, the function *ω(k)* is nonlinear. → *dispersion*; → *relation*. |

پاشش ِ هنجارمند pâšeš-e hanjârmand
*Fr.: dispersion normale*
The dispersion in which a shorter wavelength is associated with a higher
→ *refractive index*. Contrasted with the
→ *anomalous dispersion*. → *normal*; → *dispersion*. |

پیش-پاشش piš-pâšeš
*Fr.: pré-dispersion*
A technique in spectroscopy which uses a combination of several dispersive elements
(prisms in series or a grism) before focusing the light on
the primary disperser, usually a grating, in order to achieve
high spectral resolutions. → *pre-*; → *dispersion*. |

پاشش ِ تندا pâšeš-e tondâ
*Fr.: dispersion de vitesses*
The → *standard deviation* of a velocity
→ *distribution*. It indicates how objects of
the sample move relative to one another. Objects with similar
velocities have a small velocity dispersion, whereas objects with very
different velocities have a large velocity dispersion. → *velocity*; → *dispersion*. |