There are all manner of things that herald the onset of Autumn in Wisconsin: Orion poking his shoulders over the horizon on late night observing sessions, the absence of Robins, the Autumnal Equinox, and the sound of hazelnuts crunching under my tires as I pull out of my driveway.
This is also the time of year when I go outside and do not see the zodiacal light. That’s right, I really meant to say that I do NOT see the zodiacal light. That false dawn continues to elude both Amy and I, although in reality, we’ve probably seen it without realizing what it was. But to have actually gazed towards the horizon and thought, “Hey look, it’s the zodiacal light”? No, that hasn’t happened yet.
Scientists believe the zodiacal light is sunlight reflecting off the dust grains that were left over after the planets were formed in our solar system 4.5 billion years ago. It’s a really a cool phenomena if you think about it. To this day, this interplanetary dust follows the ecliptic in the narrow plane of space that is inhabited by Mercury, Venus, Earth, and beyond Mars, becoming more dense as you move closer to the sun.
In my part of the world, the zodiacal light is supposed to be most visible near the Autumnal Equinox about an hour before dawn in the eastern sky. In early spring, I get to try again to the west about an hour after sunset, but then I’m dealing with cold, damp temperatures and slippery roads, and the pursuit is even less pleasant.
I’ve read that I’m probably too far north here in Wisconsin to see the zodiacal light, although it is extremely bright and easy to see in latitudes in the southern U.S. But I’ve also heard from several of our astronomy club members that they have seen it here when conditions were right.
Now that the Autumnal Equinox is almost upon us, and the moon is rising early in the day and setting in the evening, I’m once again feeling the zodiacal light itch. And I know that if I hear that it’s going to be clear and the dew point is going to be very low overnight, I’m going to wrestle myself out of bed and try again.
Because I live in a populated area, and the zodiacal light is pretty faint this far north when it makes its appearance, I need to drive until the sky is dark enough that I can see the Milky Way. And since I need to be facing east at least an hour before the true predawn twilight (which is around 4:55 a.m.), I’ll need some serious determination to do it. But it would be worth it to catch a glimpse of the dust that’s left over from the creation of our solar system.
So any early morning now, I could find myself parked on the side of some country road facing east, groggily looking for a hazy pyramid of light extending up from the horizon. I’m predicting that, once again, I won’t see it. But if I ever do, you will be the first to know!
How about you? Have you seen the zodiacal light?