This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (i.e. when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.

Physics of Solar Prominences: I-Spectral Diagnostics and Non-LTE Modelling

This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (ie when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.

Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling

In situ measurements of the outer solar atmosphere have been conducted only down to a distance of 0.3 AU (62R ⊙) by the Helios spacecraft. Follow-on missions deeper into the corona such as the Solar Probe [2.162] are not likely to be realized for many years. As a result, the only reliable tools presently available for investigations inside of 0.3 AU are remote sensing of emissions which either (a) are generated naturally within the region, or (b) travel through the medium as a probe signal.

Remote Sensing Observations of the Solar Corona

We consider the main aspects of a rather delicate discipline, space-borne coronagraphy, which is essentially performed with white-light, externally-occulted coronagraphs. Methods of observation and recent results are presented in a scientific section; a short account of historical rocket-borne and balloon-borne experiments is also given. The review concentrates on both the NRL-type coronagraphs and the HAO-type coronagraphs, stressing the essential features and merits of numerous experiments which were flown. A small section is devoted to other designs. A large number of figures, including many drawings, are used to illustrate the growing complexity of experiments.

Space-borne coronagraphy

Photometric calibration of the LASCO-C2 coronagraph for Solar System objects

Resultats de la photometrie de la couronne solaire, obtenus durant l'eclipse solaire totale du 31 juillet 1981, ainsi qu'une analyse morphologique

C. Lebecq

Papers

The 1981 total solar eclipse corona. II. Global absolute photometric analysis.

The electron density of faint prominences observed during the solar eclipse of July 31, 1981

The 1981 total solar eclipse. III: Photometric study of the prominence remnant in the reversing south polar field