Is Betelgeuse about to blow?

Probably not, but astronomers are having fun thinking about it.

Over the last three months, the star, which marks the armpit of Orion the hunter, has mysteriously dimmed to less than half its normal brightness, markedly altering one of the great sights of the winter sky.

At the beginning of January the star was fainter than ever before observed, according to Edward Guinan of Villanova University, who has been compiling data on Betelgeuse. In its “fainting” spell, Dr. Guinan said, the star has dropped from seventh to twenty-first on the list of brightest stars in the sky. But even so dimmed, Betelgeuse is still too bright to be easily observed and measured by large professional telescopes — at least not without damaging sensors that were designed to wring every faint photon from the blackness of space.

Rebecca Oppenheimer, an astrophysicist at the American Museum of Natural History in New York, said she had managed to observe Betelgeuse with the 200-inch telescope at Palomar Observatory in California last week, but it had left an afterimage that put their detector out of service for a day. The next time around, she said in an email, they plan to cover part of the giant mirror, to cut down on the amount of light it receives.

“Ha ha, kind of ridiculous,” she wrote. “But, well, the science must go on!”

Last week Neil deGrasse Tyson, director of the Hayden Planetarium in New York, circulated a request for amateur astronomers to observe and monitor Betelgeuse’s brightness.