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Thinking Outside the Classroom: It’s not disco nights but zodiacal light

Mark Laurin
Thinking Outside the Classroom
When sunlight hits micromillimeter bits of dust particles, the light scatters, creating zodiacal light.
Getty Images

Night fever? Disco was flashy. The style, the lights, the music was glitzy and sensational. It was best represented by the ubiquitous mirror ball, spreading scattered specks of light everywhere. Remember New York City’s Studio 54? Maybe not. Anyway, there is a similarity between a disco mirror ball and the zodiacal light.

What is zodiacal light?

Our solar system is filled with tiny, tiny bits: particles and pieces of dust debris from active comets, dormant comets and collisions between asteroids in the asteroid belt. The dust, due to the forces of motion and radiation, moves in a circular motion forming a thin, flat, ovular cloud. The cloud resides roughly in the area of outer space between Earth and Jupiter. When sunlight hits these micromillimeter bits of dust particles, the light scatters. Zodiacal light is the result. When the light scatters forward, toward us, it is seen as magnitudes brighter. Similar to — you guessed it — a mirror ball.

Why look for zodiacal light now?

We are approaching the vernal equinox, so no matter your location in the Northern Hemisphere, the ecliptic’s angle to the horizon steepens as we inch closer to March 20, making the zodiacal light easier to see.



You can see the zodiacal light in the evening so no need to get out of bed at zero dark thirty. For those residing in the Mountain West, especially here in elevated Summit County, fortune favors us. When we look to the western horizon, we look through less atmosphere to distort our view. We are gifted with clear and clean viewing.

The zodiacal light is conical, or triangular in shape, wider and brighter at the base on the horizon with the tip of the cone pointing toward the ecliptic arch. The light is subtle, faint and diffused, yet clearly visible. Under the darkest of moonless skies, zodiacal light is seen spanning the entire length of the ecliptic, from horizon to horizon. The ecliptic is the plane of Earth’s orbit around the sun projected upon the celestial sphere. The 12 astrological zodiac signs, for the most part, reside along the ecliptic. Thus the name.



Seeing zodiacal light

You can see the zodiacal light with your unaided eye after sunset as twilight deepens. Pick a clear night and get away from light pollution. A moonless night, or before the moon’s first quarter, is best. On top of a mountain pass is ideal. Look west, and then imagine the sun’s path across the sky to the point where it sets.

Looking in this direction, about one hour after sunset, notice a faint glow of an upside-down ice cream cone sitting on the western horizon. The glow is similar to that of the Milky Way but more uniform and consistent. It’s called a false dawn since the sky is glowing near the horizon. The difference between the two is the cone of light shooting up from the horizon points up across the ecliptic. You don’t see this at dawn.

The zodiacal light is a spectacular sight, and I hope you get out one evening to see it. And if you want to listen to a little disco music to better enjoy the cosmic mirror ball, who am I to judge?

Clear skies!

Mark Laurin

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