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Writing about the glory seen on Venus for my post yesterday reminded me that a couple of years ago I saw a good one while flying home from a talk I gave in Texas. I took some video on my camera, but never did anything with it for various reasons, mostly due to the loud airplane noise and muted colors in the video. But I figured what the heck, I can edit it a bit, bring out the colors and suppress the airplane engines. So I did. I’m actually pretty happy with this:
Cool, huh? (The transcript of what I said is below if you had a hard time hearing me.) A glory is pretty amazing to see for yourself; the colors can be quite vivid, and it’s mesmerizing to watch it “follow” you across the clouds.
It gets even better if you can see one as the plane starts to descend; the apparent size of the glory stays the same (because it depends on the angles at which the light is bent and is not a solid, physical thing, much the same way a rainbow always appears to be the same size in the sky), but as you get closer to the cloud you can see the airplane’s actual shadow. Because the glory is centered on your head, if you’re sitting in the back of the plane, say, then you actually see the glory centered on the back part of the airplane’s shadow! I’ve seen this myself a few times, and it’s seriously freaky, especially if you can watch the airplane shadow grow in size while the glory stays constant. It’s truly astonishing.
In the video I talk about double reflections inside droplets breaking up the sunlight into colors and sending it back the way it came so you can see it, but it turns out things may not be that simple. I haven’t been able to find a definitive explanation for what causes glories, which is interesting. If anyone knows of any, please let me know! Given that some of the colors are repeated outside the main bright glory (you can see that faintly in the video) there are either multiple internal reflections inside the droplets, or there are constructive/destructive interference effects I can’t quite put my finger on. I’d love to know more about this.
The airplane noise was loud, so in case you couldn’t hear it clearly, here’s what I said:
Hey, Phil Plait from BadAstronomy.com here. I'm actually on an airplane at about 32,000 feet (10,000 meters) up. I'm flying home from giving some talks in Tyler, Texas. I looked out the window and it's pretty cloudy out there, we're somewhere over maybe northern Texas, Oklahoma, Kansas, it's hard to say I don't know exactly where, but it's pretty cloudy way down below us. As I'm looking out I'm seeing something pretty cool. Let me reverse the camera and show you this.
There, do you see it? There's a circle of light just under those clouds where I've got the frame centered. And it's colorful, I can see a red ring, yellow, green, and then it's bright in the center. That's called a glory. It's an optical effect where light hits clouds and gets bent directly back toward you. And it only happens when there're certain types of clouds. I see it from airplanes all the time, but this is the first time I had a video camera ready to go.
You can see it getting brighter and fainter as the clouds change as we move. I've taken some pictures of it and it looks pretty clear sometimes and other times it completely disappears. But this only happens when you're looking straight down the path of sunlight so right now the sun is directly behind me and I'm looking straight down the path. The sunlight hits the cloud, it gets bent internally inside of the cloud ice crystals or water droplets and then it comes straight back. See now it's fading; you can hardly see it at all.
Funny—I always say that people should go outside and look up. But sometimes it's worth looking down, too.