Measurements of the Gegenschein from Space

Abstract

THE zodiacal light, which is produced by light scattered from small interplanetary particles, gradually declines in brightness with increasing angle of elongation, ɛ, from the Sun. As the anti-solar point (ɛ= 180°) is approached, the surface brightness again increases slightly to produce the counter-glow or gegenschein. This diffuse feature can be best observed against the sky background when it lies outside the region of the Milky Way. Fig. 1 depicts the sky background brightness at the anti-solar point as a function of time throughout the year. The integrated light from stars predominates during the two Milky Way traverses. Observations of the gegenschein are made best away from the Milky Way in February, March and April, or in August, September and October.