Full circle rainbows can be seen in nature, but you’ve got to be in the right place at the right time to spot one. The fact is that actually, all rainbows are circular, but we’re always viewing them from the ground. This means the lower half is blocked from view, but if you get to the right height, you’ll be treated to a full circle rainbow.
A stunning example of a full circle rainbow was caught on camera by construction workers at the Lakhta Center in Saint Petersburg, Russia. The 87-story skyscraper stands at 462 meters (1,516 feet) tall, making it the tallest in Europe and the 16th tallest in the world. That also makes it a fine viewing point for seeing full circle rainbows.
The reason you’ve got to be high up to view full circle rainbows is because in order to see them there must be water droplets below your observable horizon. That will only happen if you’re a long way off the ground.
“A rainbow's centre is directly opposite the position of the sun in the sky, so more of a rainbow can be seen as the sun approaches the horizon,” explained the UK Met Office. “Therefore you will normally see the greatest percentage of a rainbow (50 percent) at sunrise or sunset.”
This means that aircraft are also a good place for spotting full circle rainbows. In fact, aircraft get treated to all sorts of fun tricks of the light as something called “pilot’s glory” (get your head out of the gutter) can be seen when an optical illusion makes it appear like a plane’s shadow is being lit up by a rainbow-colored halo.
Also known as a glory or pilot’s bow, pilot’s glory is produced by similar processes that create a rainbow, but with a twist. The phenomenon actually has very little to do with the shadow. It simply occurs in the same location as the shadow because this is the antisolar point, the point directly opposite the Sun from an observer's perspective. In other words, the Sun is directly behind the shadow and the glory from the viewer.
High up in general is a good spot for fun with the sun, and there are many excellent photographs and videos of people making the most of Brocken specters. The nifty optical illusion was first observed on the Brocken peak in Germany, earning it the local name Brockengespenst.
It happens when a person or object creates a shadow that then gets a leg up by casting onto a cloud or mist. The combination results in an enormous shadow that looks really far away and occasionally moves, even if the person or object casting it remains still.
They can look pretty creepy if you’re out walking alone, sort of like a psychedelic spirit is tracking you through the fog. Not helped of course by the fact that if you start running, a bit like pilot’s glory, that thing is coming with you.
With plane-hunting orbs and creepy rainbow stalkers on the loose, suddenly a full circle rainbow doesn’t seem so strange, but that doesn’t make them any less beautiful. Another time you might see a full circular rainbow is when it’s a moonbow surrounding Earth’s faithful friend, but did you know there’s also something different called a moon halo?