The full moon is tomorrow, and it reminds me of the astronomical wonders I saw a month ago, on a backcountry ski trip.
First up was a “Supermoon.” This is a full moon that coincides with the moon’s closest pass of the year to Earth. Tomorrow’s full moon will be a supermoon as well (50,000 km closer to Earth than the full moon this coming September), and it should look amazing! Supermoons are noticeably bigger and brighter than regular full moons. I snapped this shot a few days before the moon was full, as it cleared the peaks near Mistaya Lodge. When my ski mates and I looked up and saw it, we all said, “wow,” as it looked so impressive.
Along with the moon, we were treated to a solar light show as well. February was one of our coldest on record, and when it’s that cold, for weeks in a row, we often get lots of sparkly ice crystals in the atmosphere. This is the result:
Holy diffractionation, Batman!
All those ice crystals are reflecting and refracting light from the sun. The big circle around the sun is called the 22 degree halo, and the bright spots on the right and left are nicknamed “sundogs.”
But there can be more than just that, and a month ago, we got the whole show. There were things I’d never seen before: the Parry arc, the parhelic circle, and the coolest thing of all, an upside-down rainbow way up above the sun called the circumzenithal arc. It looked like a giant happy face:
I had to look all this stuff up to understand how it worked. If you want a rundown of all the pieces of the puzzle, this Smithsonian article is really good.
There’s also a lot of good diagrams online, and since I love history, I found a reproduction of the first diagram to illustrate the physics of all this bending and reflecting light. It was drawn by polar explorer William Parry in the 1820s:
Happy moon watching tomorrow!
