It was one of several recent sightings in the sky to cause talk about U.F.O.s. Others included a group of strangely shaped clouds over Cape Town, also over the weekend, and an Army veteran’s claim that he spotted a “solid, dark-gray triangle-shaped craft” in the sky over Portland, Tenn., last week. Most of these sightings go unreported in the mainstream news media, though a variety of blogs and sites track them.

“The mind abhors a vacuum of explanation,” said Michael Shermer, 61, the publisher of Skeptic magazine and a columnist for Scientific American. “Short of a good explanation, people just turn to the one that most immediately comes to mind which, in pop culture, is extraterrestrials.”

A poll of a random sample of 1,114 American adults conducted by National Geographic in 2012 found that 77 percent believed “there are signs that aliens have visited Earth.” (It also found that President Obama would “handle an alien invasion” better than Mitt Romney, who was running for president at the time.)

Another, more rigorous survey frome Time and CNN conducted in 2000 found that 20 percent of respondents said they knew someone who had seen a U.F.O.