Zodiacal Light

The Zodiacal light is composed of fine particles of dust in orbit around the sun and is visible because of scattered sunlight from the particles. The glow is brightest toward the sun from particles with diameters between a couple of micrometers and a few millimeters.

From the mid-northern latitudes, the Zodiacal light is most easily visible from a dark location under clear and transparent skies just after evening twilight in the west in February and March, and in the morning eastern sky, just before the start of twilight in October.

It is best seen at these times because the plane of dust that comprises it lies in the same plane as the ecliptic, and the ecliptic is at it's steepest angle to the horizon at these times of the year.

Many people confuse the Zodiacal light with twilight since it occurs in roughly the same area of sky, although careful attention to the time of the true end of astronomical twilight will remove any doubt about whether you are seeing the Zodiacal light or the sky brightening from lingering twilight.

In mid-northern latitudes, the zodiacal light is best observed in the western sky in the spring after the evening 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 either moonlight or light pollution. The zodiacal light decreases in intensity with distance from the Sun, but on very dark nights it has been observed in a band 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 also a very faint, but still slightly increased, oval glow directly opposite the Sun which is known as the gegenschein.

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