Federal Aviation Administration spokesman Ian Gregor says he got calls about the object all afternoon Monday.
Bill Stepp of NASA's Columbia Scientific Balloon Facility in Palestine, Texas, says the mysterious flying orb was a 4,000-pound NASA research balloon used to measure gamma ray emissions.
Stepp says the balloon usually floats at 130,000 feet and can be seen for about 170 miles on a clear day.
Jennifer McCoy, who runs a UFO-themed Store in Sedona with her husband, says it "looked like the gigantic bubble from the Wizard of Oz."
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