“We’re seeing something that’s coming into the atmosphere at very high speed, fast enough that the friction with the Earth’s atmosphere causes it to begin to vaporize,” said Jim Lattis, an astronomer at the university.

Hundreds of fireballs streak across Earth’s atmosphere every day, Dr. Lattis said, but people witness few of them. The majority fly over uninhabited areas, and many also occur during daytime when the sun’s glare makes them hard to detect.

“For someone who doesn’t spend much time looking at the sky, seeing something like this could be a once in a lifetime experience,” he said.

In total, the A.M.S. website received more than a thousand reports about the two events. Using that data, the organization can estimate the velocity and trajectory of the fireballs, according to Mike Hankey, the operations manager for the A.M.S.