What is this mysterious black ring flying over West Bridgford, Nottinghamshire, UK?
Looks like a transformer at a power substation blew out. But still awesome!
This strange sky phenomenon is called a Vortex smoke ring.
As shown in the next video, something on the ground was either set off or exploded, forming this type of smoke cloud:
And here a video of one forming during the Georgia power substation explosion at Morgan Falls Dam on May 11, 2011:
Usually, tube shapes, such as volcanos and smoke stacks also contribute to this type of strange sky phenomena.