Issue EAS Publications Series Volume 18, 2006 Radiative Transfer and Applications to Very Large Telescopes Page(s) 1 - 23 DOI 10.1051/eas:2006002 Published online 08 March 2006

Radiative Transfer and Applications to Very Large Telescopes
Ph. Stee (ed)
EAS Publications Series, 18 (2006) 1-23
DOI: 10.1051/eas:2006002

Why is it so difficult to solve the radiative transfer equation?

B. Rutily¹ and L. Chevallier<sup>2

1</sup>  Centre de Recherche Astrophysique de Lyon (UMR 5574 du CNRS), Observatoire de Lyon, 9 avenue Charles André, 69561 Saint-Genis-Laval Cedex, France;
²  Observatoire de Paris-Meudon, Laboratoire LUTH, 5 place Jules Janssen, 92195 Meudon Cedex, France;

rutily@obs.univ-lyon1.fr
loic.chevallier@obspm.fr

Abstract
The equation of transfer is a two-faced equation, easy to solve at times, and difficult to solve at other times, depending on the values assumed by its coefficients. It is rather tractable when applied to the deep layers of atmospheres and for frequencies from their continuum spectrum, but this solvability is in stark contrast to the difficulty in solving it close to the surface of atmospheres or within spectral lines. It follows that the photons most rich in information that reach our telescopes are also the most difficult to interpret. The purpose of this note is to stress this point and to illustrate it with some examples taken from the solar atmosphere.

© EAS, EDP Sciences 2006

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