The Front-to-Back Asymmetry of Coronal Emission

Several recent papers have considered the observation of halo coronal mass ejections (CMEs) using the assumption that coronal emission is symmetric with respect to angular position from the Sun. This paper presents a simple but rigorous treatment of the observation of a single electron in the solar corona. The brightness of an electron as a function of height and angle from the solar limb is presented. The conclusion is reached that there is a front-to-back asymmetry of coronal emission that becomes significant at large angle and/or large height. The observation of halo CMEs is considered. The suggestion is made that a mass cut-off makes it likely that halo CMEs will be more massive, wider, and faster than the typical CMEs. Front-side halos should be more commonly observed than CMEs from the back side.