Are they errant smoke rings or alien-controlled ships from Circleworld? Watch these videos of the "ring UFO" phenomenon and judge for yourself.
Photograph by Paul Sonne.
Here's a 2008 ring sighting in the Rocky Mountains, right in the middle of the day:
And another day sighting in Arizona, from an airplane window:
Here's a California sighting from earlier this year, complete with stoner voiceover:
Apparently the first ring was sighted in 1957, and reported in a few papers as a bizarre phenomenon that started as a gleaming ring and slowly faded into a cloud formation. Many people believe that these ring sightings are, in fact, smoke rings that form naturally (like the one at the top of this post) and from a distance appear to be ships.
You can learn more about ring UFOs over at the UFO Disclosure Countdown Clock blog.