The Zodiacal Light

Have you ever been out on a very dark, moonless night after all the remnants of sunlight have faded away and noticed a faint triangular shaped glow extending upwards into the sky?  This relatively rare phenomenon is called the Zodiacal Light.  Why is it rare?  Conditions have to be good to see it because moonlight and light pollution can easily hide it.

The best time to view the Zodiacal Light in the northern hemisphere is in the spring just after twighlight has completely disappeared.  Look in the sky above where the sun set and you should see a pale glow of white light extending upwards and tilted toward the plane of the ecliptic.  You can also see it in the northern hemisphere in the fall just before sunrise. 

The Zodiacal Light phenomenon was first studied by one of our favorite early astronomers, Giovanni Cassini in 1683.  It gets its name from the fact that the light appears to extend along the plane of the ecliptic or zodiac.

Zodiacal Light is caused by sunlight bouncing off dust particles in the solar system.  Sometimes referred to as the interplanetary dust cloud, these dust particles orbit around the sun and due to gravitational forces, flatten out into a disk.  Since the reflection of sunlight is brightest when seen at a small angle to the sun, the best time for viewing is right after sunset (or right before sunrise) while the bright light of the sun is blocked, but the reflection from the dust particles is not.

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