Have you ever been flying over a cloud deck and noticed a rainbow halo around the shadow of your airplane? Besides being pretty to look at, this ring-shaped rainbow – called a pilot’s halo or glory of the pilot because we’re usually the only ones who get to see it – should be a clue to you that the cloud holds liquid moisture.
Glories are common. They’re seen all the time by people traveling in airplanes. You need the sun to be directly behind your head. In front, you need an ordinary cloud. As you look toward the cloud, look for the shadow of the airplane. The plane’s shadow may be surrounded by a multi-colored circle of light.
The plane’s shadow doesn’t have anything to do with making the glory. The glory and the shadow just happen to be located in the same direction – opposite the sun.
EarthSky explains that the glory must intersect with an anti-solar point, or a spot that “faces the opposite direction to the sun,” according to EnglishDictionary.com. The sun's light scatters among droplets in the cloud instead of on falling rain (which is what causes the arched rainbow shapes we're used to seeing from the ground).
And thus glories are commonly observed from very tall buildings or from airplanes. Before the days of air travel, people spoke of glories they’d seen while mountain climbing. The same conditions – the sun behind and a cloud ahead – can also cast your shadow onto the mist. Then it’s possible to see a glory around the shadow of your own head. That type of glory is called a brocken spectre.
You can also spot a glory from tall buildings, hot-air balloons, mountains, or any other spot that can get you above a veil of clouds. Glories are not something you see every day, so if you’re lucky enough to spot one, definitely take a photo.