The Biggest Dust Bunny In Town

The zodiacal light slants up from the northeastern horizon and tips to the right in this photo taken this morning at dawn (5 a.m.). The light is brightest at its base, where the dust particles are closer to the sun and reflect its light more strongly. From there, the light cone tapers and fades as it extends nearly half-way up the eastern sky. The small clump of stars near center is the Beehive Cluster in Cancer. Photo: Bob King

It’s BAAACK! And it’s the biggest thing in the solar system you can see with your naked eye. We’re talking about the zodiacal light, the softly luminous glow of reflected sunlight from countless dust particles shed by comets and stirred up by tug of Jupiter’s gravity. Like the planets, the dust resides in the plane of the solar system. And since we see the planets cycling through the zodiac constellations, that’s also where we see the cone or wedge-shaped zodiacal (Zo-DIE-uh-cull) light.

The light is a subtle thing, and you’ll need the dark sky afforded by an outer suburb or the country to see it with certainty. When I walked out the door this morning from my home near Duluth, the first hint of it was a big glow low in the northeast that one could easily have mistaken for light pollution from a nearby city. Once my eyes got used to the dark, I could see a faint wedge of light extending upward and to the right all the way to the top of Orion and the winter Milky Way. At its apex, the light was faintest, making it hard to say exactly where it terminated. Sweep your gaze in broad strokes back and forth across the eastern sky to help you discern its distinctive conical shape. And be sure to look for something HUGE. This is a very extensive, if faint, glow.

The combined glow of dust particles in the plane of the solar system reaching from the sun's vicinity to beyond Mars is responsible for creating the zodiacal light. Planets are shown as colored disks. Illustration: Bob King

The best times to view the zodiacal light for northern hemisphere observers is at dawn now through October and at dusk in the early months of spring. During both times, the slant of the ecliptic (plane of the solar system) is at its steepest, allowing the light cone to jut nearly straight up into a dark sky. At other times, its slant is so shallow, the dusty glow is lost in the horizon haze.  For the current display, the best viewing time is at the cusp of dawn 1 1/2 to 2 hours before sunrise. If you’re out much later than that,  twilight takes over. Too early and the light cone is too low for easy viewing.

Because the zodiacal dust cloud extends at least to Jupiter on both sides of the sun, it’s the biggest single feature of our solar system visible without optical aid.  We can only see about 1/2 of its true extent at any time because the other half is in the daylight sky. That means the cone you see at dawn extends across some 500 million miles or more than 500 times the size of the sun. Truth be told, from the very darkest sites, the zodiacal cone tapers into a band that encircles the entire sky, expanding its girth even further. While the individual dust particles are tiny and spread apart, if you could gather them together and pack them all into a tiny ball, they would far outshine Venus. Dust is so amazing.

Read more about recent zodiacal light research HERE.

Tonight the thickening crescent moon will be near the bright red supergiant star Antares in the constellation Scorpius the Scorpion. The three stars in a row to the right of the moon make up the scorpion's head. Created with Stellarium

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