With autumn’s start this week, we’re officially beginning our colder season. And it produces one effect that’s not widely recognized. The reduced sunlight strength sufficiently cools the air above us that it’s increasingly common to stand below clouds made not of water droplets, but bits of ice. These crystals are almost always six-sided and have very specific (and glorious) effects on sunlight hitting them. One of them is to create the common 22° halo.
In our region, we see such haloes once or twice a week on average. Whenever high thin clouds fill the sky, look far around the Sun, and you’ll observe haloes frequently. I say “far around the Sun” because the invariable 22-degree radius means it’s a huge phenomenon. By chance, an outstretched hand with fingers and thumb maximally spread apart will mark off 22 degrees when held at arms’ length. So if you place your thumb on the Sun, your pinky tip will always touch the halo. At arms’ length, remember.
These halos normally display little or no color, or sometimes have red on the inside. If the Sun is lowish, there will commonly be a sun dog directly to the left or to the right of the Sun, or in both places, right on the halo itself, as in the photo on this page. Science nerds call them by their proper name – parhelia – but “Sun Dogs” have been commonly used for centuries. The halo, the Dogs, the whole thing is due to those hexagonal ice crystals.
But like everything else, they give rise to misinformation, some of it paranoid in nature. On one website, someone commented that the government is dropping tiny metal fragments from planes in an effort to control climate, though some claim it’s for mind control. This writer said, “Those aluminum particles are causing rings around the Sun. I never saw a ring all my life, but now I see them frequently.”
It’s true that once you start watching the sky, you see stuff that previously eluded you. Haloes have always been common, but how many people watch the sky? Anyway, one bit of folklore about them is actually accurate: supposedly they portend the arrival of stormy weather within 24 hours. This is often true because high ice-crystal cirrus clouds usually arrive first, followed by lower and lower cloud layers until the thick, pure-water overcast clouds finally bring the rain.
Another thing to look for is whether there’s a bowl-shaped “letter U” with flared upper ends seeming to balance atop the halo. This is the famed “upper tangent arc” and is one more ice-crystal presentation. So gaze around the Sun whenever high clouds are there. It’s a lot of fun, it’s Covid-safe and the price is right.