I arrived just after 9 p.m. in the parking lot of a PetSmart about 1 mile west of Uptown Sedona, Arizona, and walked up to a purple van. The sky was clear, and the last embers of sunlight had almost faded, leaving the desert on the verge of darkness: perfect conditions to search the night sky for UFOs. Peter Sterling, who has silver-flecked hair and a cherub-like face weathered by the desert sun, greeted me and photographer Andrew Friendly before we climbed into the van and headed into the de...