No. 93: May-Jun 1994
The spacecraft Clementine, now engaged in surveying the moon from orbit, has apparently recorded once again a perplexing sky glow that precedes lunar sunrises and follows lunar sunsets. An astronaut standing on the moon watching the spot where the sun is about to rise would see first of all two well-recognized phenomena: the solar corona (even though the solar disc is still well below the horizon) and the zodiacal light (sunlight reflected from interplanetary dust). In addition, the astronaut would detect a glow along the horizon itself, as in the illustration. Since the moon is virtually airless, there should be none of those gas molecules and suspended dust particles that cause the sunsets and sunrises that we admire so much here on earth. Still, there must be something suspended above the moon's surface to scatter light from the sun still located just below the horizon. The best guess is that lunar dust particles are ionized by solar radiation and are repelled upwards from the surface and hang there suspended by electrostatic forces. But no one really knows for certain the cause of the glow.
(Cowen, R.; "On the Horizon: Clementine Probes Moon Glow," Science News, 145:197, 1994.)
Reference. Anomalous lunar horizon glows are cataloged in ALO11 in our catalog: The Moon and the Planets. For details, visit here.