The sequence of images on today's cover of Eos shows the most spectacular solar mass ejection observed to date with the Naval Research Laboratory's Earth-orbiting coronagraph. Preceded by a loop-shaped coronal structure, an enormous eruptive prominence is visible both expanding and moving outward across the coronagraph's 2.5–10.0-RS annular field of view. As it left the field, the prominence dwarfed the sun itself, whose size and location are indicated by the small white disk in the lower-right photograph.

The prominence can be recognized by its characteristic structural detail and by the fact that its relatively unpolarized radiation is not blocked by the polarization-analyzing rings that are faintly visible at 5 RS and 8 RS against the coronal background. The Ha 6563α line of neutral hydrogen is the principal prominence emission line in the coronagraph's 4000–7000-A spectral bandpass. On the other hand, the strongly polarized coronal radiation is continuum emission originating at the occulted solar disk and Thomson scattered by coronal electrons in the 2.5–10.0-RS field of view. Both the prominence and the expanding coronal ‘loop’ have been enhanced in our cover photograph by subtracting a preevent image from each picture.