The zodiacal light is a faint glow which appears in a band along the ecliptic or zodiac from the vicinity of the Sun. It may be best observed in the western sky in the spring after the sunset twilight has completely disappeared, or in the eastern sky in the autumn just before the morning twilight appears. It is so faint that it is completely masked by moonlight. The zodiacal light decreases in intensity with distance from the Sun, but on very dark nights it has been observed completely around the ecliptic. In fact, the zodiacal light covers the entire sky, being responsible for 60% of the total skylight on a moonless night. There is a slightly increased illumination of the zodiacal light directly opposite the Sun known as gegenschein.
Zodiacal light is produced by sunlight reflecting off particles of dust present throughout much of the solar system. The amount of material needed to produce the observed zodiacal light is amazingly small; if it were in the form of 1mm particles each with the same albedo (reflecting power) as Earth's moon each particle would be 5 miles from its neighbours. The material producing the zodiacal light is located in a lens-shaped volume of space centered on the sun and extending well out beyond the orbit of Earth. The gegenschein may be due to the fact that particles directly opposite Earth from the sun would be in full phase.
See also: Optical phenomenon