When you looked up on Thursday, you probably saw what looked to be a colorful rainbow around the sun. It wasn't actually a rainbow, but a halo. With each picture I received, the same question was asked...how do these form?
First, it's important to know that white light coming from the sun contains every color known to man. When that white light passes through a raindrop or ice crystal, each color is bent slightly and sent in a unique direction, creating the spread of colors we see. When raindrops are involved, the spread of colors appears as a bow across the sky. Since ice crystals are six-sided, the light is refracted differently creating a ring around the sun or moon.
Halos, like those you saw Thursday, are very common and form because of the presence of high, thin cirrus clouds entirely made of ice crystals. Interestingly, if you had a protractor handy (and who didn't?) you would've measure a perfect 22-degree angle between the center of the sun and the actual halo.
In a few of the photos, I noticed another interesting and rare optical phenomenon known as an Infralateral Arc. A what you ask? Just two weeks ago I asked that same question because of another photo sent to me by a friend in Florida. I dusted off the old meteorology books and found Infralateral Arcs are only present when the sun is high in the sky. I also found that the greens and blues easily seen in the photo distinguish the Arc from the even rarer 46-degree halo.
It's amazing what happens to light when it passes through raindrops or ice crystals. Thankfully, these phenomena are completely harmless. You may laugh, but I once got an email telling me that halos are "the eyes of life forms from distant galaxies preparing their takeover of the world". Sleep tight!
