> Scientists believe they must occur thousands of times a day, but until this most recent study, only 16 had ever been detected. They seem randomly distributed

> Scientists believe they must occur thousands of times a day, but until this most recent study, only 16 had ever been detected. They seem randomly distributed throughout the sky, and no one is sure what causes them. They are said to happen more frequently than a few times a year. I'm guessing it's just that we are not detecting the bulk of them because they're randomly distributed.