Driftless Dark Skies

John Heasley

We’ll carry with us many memories of the summer of 2020, but one of my favorites will be the three weeks in July when Comet NEOWISE had so many of us looking up together/apart being awed in a dark time by this visitor from far beyond. It was wonderful to hear from so many skywatchers in the Driftless Area and beyond who spotted the comet and shared pictures and reactions and made memories with family and friends. For many, it was a first time glimpsing a comet. 

Comets are traditionally named for their discoverer, so this one is named for the Near Earth Object Wide-field Infrared Survey Explorer — a space telescope that is watching for things that might cross our path. Like that comet or asteroid that wiped out the dinosaurs 66 million years ago. But comets are the bringers of life as well as death. Much of Earth’s water comes from comets. And comets are also the bringers of meteors. With each flyby of the sun, comets might lose 1/1000 of their ice and dust. When Earth flies through that trail, pieces of comet dust streak across our skies and we see meteors such as the Perseids in August. So this comet could be around tens of millions of years old. But just a short time in a cosmos almost 14 billion years old.

NEOWISE first spotted its comet on March 27. Many comets break up when they swing by the sun, but this one survived its flyby July 3. The sun heated up this “dirty snowball,” evaporating its ice and creating a coma (cloud) around its nucleus and a tail millions of miles. That’s what had me awestruck when I headed out before dawn July 7 with my binoculars and spotted it low in the northeast. Best comet I have seen in 20 years. And it got even better as it rose higher in the sky, grew brighter, and then became visible in the evening. I loved that it was so easy to spot as it moved through the Great Bear.

The comet was also an invitation to ponder deeper time. This comet was formed over 4 billion years ago in the early days of our solar system and has spent most of its time in the far frigid dark reaches of the Oort Cloud. Something disturbed its orbit, and it began falling toward the sun. In this warmer neighborhood, it developed that distinctive tail. When Comet NEOWISE last passed by Earth 4400 years ago, humans were just starting construction of Stonehenge. Its recent flyby of our sun has lengthened its orbit to almost 7,000 years. In the next 35 centuries, NEOWISE will journey far out into our solar system 700 times the distance of Earth to the sun (and 15-20 times the distance of Pluto) before falling back in for another fleeting flyby of the sun (and Earth) sometime around the year 8800. Hope our descendants are as awed as we were and they remember us as good ancestors.

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. For more information about stargazing in southwestern Wisconsin, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies above.