Mind blown
This video, shot by a crane operator working on the 1,500 ft tall Lakhta Centre skyscraper in St Petersburg, Russia, shows it in all it's round glory.
In theory, every rainbow is a circle, but thanks to the Earth's curvature, only the upper half can be seen. Go to a higher point, like the top of a construction crane or an airplane, and rainbows are revealed to be a complete circle.
Moar: http://www.physicsclassroom.com/class/refrn/Lesson-4/Rainbow-Formation
Wow, how cool is that? Thanks for sharing.