I was in the middle of making tea this morning when I looked out the window and saw the most amazing diamond dust halo display. Tea would have to wait. I got in the car instead and drove to the nearest opening to get a good look at the rare phenomenon. Ordinary, ice crystals in cirrus-type clouds create halos and sundogs, but this morning, with the air temperature at –18° F (–28°C), ice crystals formed directly in the air near ground level.
Under a cloudless sky, two bright arcs flanked either side of the low sun from which a spectacular light pillar rose to intersect a faint half-halo. Blocking the sun with my gloved hand, I could see the ice crystals — called diamond dust — that created the display blowing past in a light wind, flashing and sparkling.
Diamond dust is like fog but it’s made of water that directly crystallizes from the humidity in the air. It even looks like fog but thinner. Looking down the road, I saw it as a haze in the distance. Although fairly common in the Arctic, it’s not so much in the lower 48 except in extreme cold. Conditions have been ideal here in northern Minnesota and Wisconsin the past week, but this is the first morning I’ve seen it.
With temperatures in the Upper Midwest forecast to be well below zero at night for the coming week, I encourage you to keep an eye out for this beautiful and colorful sight.
Tonight, the waxing gibbous moon will occult (cover up) the bright, orange star Aldebaran from about the eastern two-thirds of North America. The event happens in a dark sky from the eastern states and in twilight in the Midwest and shortly before sunset from the mountain states. It’s easy to watch because all you have to do is find the moon, which will be up in the eastern sky. The occultation happens at the left (eastern) edge of the moon around 6 p.m. Eastern time; 5 p.m. Central and 4 p.m. Mountain. For specific times, click here for a list of hundreds of cities with times of the star’s disappearance and reappearance. Times are given in UT or Universal Time. Convert to Eastern by subtracting 5 hours; Central 6 hours; Mountain 7 hours and Pacific 8 hours.
For many of us, this event gives us a shot at seeing a star in early twilight or even before sunset in binoculars. Once you’re focused on the moon, look to its left (east) for a tiny spark of orange light. As the moon moves eastward in its orbit, it will edge up to and then suddenly cover the star in an instant. No matter how many of these you’ve seen, the disappearance always feels like a surprise. Aldebaran will re-emerge on the opposite side (west or right) side of the moon minutes to about an hour later depending on your location.
Enjoy this event as it will be the last widely visible Aldebaran occultation until the year 2033!