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Zodiacal light is a faint, whitish, triangular glow that appears to extend up from the area of the Sun along the zodiac(ecliptic). It is caused by sunlight scattered by space dust in the zodiacal cloud. It is faint enough that moonlight or light pollution in general will block it out. The zodiacal light covers the entire sky and accounts for 60% of the total skylight on a moonless night.
In the mid-latitudes, the zodiacal light is best observed in the western sky after evening twulight has completely disappeared(in spring) or in the eastern sky before morning twilight appears(in the autumn). It appears as a column and is brighter at the horizon, while tilting at the angle of the ecliptic. Light scattered from extremely small dust particles is forward scattered, so the zodiacal light is brightest when observed at a small angle with the Sun. This is why it is most clearly visible near sunrise or sunset, when the sun is blocked, but the dust particles nearest the line of sight to the sun are not.
Zodiacal light is produced by sunlight reflecting off cosmic dust and its spectrum is the same as the Sun’s. The dust is located in a lens-shaped volume of space centered on the Sun and extending well out beyond the Earth’s orbit. Most of the material is located near the plane of the solar system and that explains why the zodiacal light is seen along the ecliptic. The amount of material needed to produce the observed zodiacal light is amazingly small. If it were in the form of 1 mm particles, each particle would be 8 km from each other. The Poynting-Robertson effect causes the particles to spiral slowly into the Sun, so a continuous source of new particles is needed. This material is generated by cometary dust and impact events in space.
We’ve also recorded an entire episode of Astronomy Cast all about Space Dust. Listen here, Episode 128: Dust.