Lunar dust motion.

Surveyor 7 photographed a bright glow along the western lunar horizon one hour after local sunset. This horizon glow must result from the forward scattering of sunlight by a swarm of dust grains extending 3 to 30 centimeters above the local horizon with a column density of 5 grains/sq cm. The observable glow is evoked by grains approximately 6 microns in radius. An annual churning rate of .001 g/sq cm is implied. A model is presented for dust cloud production in terms of electrostatic levitation of lunar surface fines.