The star known as Betelgeuse used to be one of the brightest objects in our night sky. In fact, it was easily discernible to the naked eye, gleaming brightly from the shoulder of the constellation Orion.

And that's to be expected from a star that's not only relatively close to us, but also classified as a red supergiant, puffing up about 700 times as wide as our own sun.

But lately something has been eating Betelgeuse. As researchers at Pennsylvania's Villanova University have repeatedly shared in The Astronomer's Telegram, the star has turned down the lights dramatically in the last few months. Scientists say it's at least 25% less luminous than its usual brilliant self — going from the ninth brightest object in the sky to the 21st. (And if you don't know where to look in the night sky, see Astronomy Picture of the Day by Jimmy Westlake offers a quick, visual how-to guide.)

Betelgeuse is dimming, ESO comparison This comparison image shows the star Betelgeuse before and after its unprecedented dimming. The observations, taken with the SPHERE instrument on ESO's Very Large Telescope in January and December 2019, show how much the star has faded and how its apparent shape has changed. (Photo: ESO/M. Montargès et al.)

As a variable star, Betelgeuse waxes and wanes in brightness as part of a natural cycle. But it's losing its shine so fast, that now telescopes can see its transformation in slow motion. In fact, astronomers suspect it may be primed to go supernova.

When a star comes to an end, it often dims before unleashing a luminosity that's exponentially greater than usual. Supergiants don't typically die boring deaths.

And if Betelgeuse does explode, its proximity to Earth would make it a blinding beacon in the sky, day or night.

"I personally think it's going to bounce back, but it's fun to watch stars change," lead study author Ed Guinan tells CNN. Although, he adds, if Betelgeuse keeps losing its shine, "all bets are off."

A chart showing size of Betelgeuse compared to our sun. Our sun barely registers as a pinprick compared to Betelgeuse. (Photo: Aliona Ursu/Shutterstock)

Guinan, who has been observing Betelgeuse for decades, says the star's distance from us makes an accurate diagnosis impossible. (Guinan and other astronomers at Villanova have been measuring Betelgeuse's brightness for about 40 years, and the star is the dimmest they've ever seen it.)

"What causes the supernova is deep inside the star," Guinan adds.

The thing is, since it's roughly 650 light-years from Earth, Betelgeuse may have already issued its last sigh. That's because the news of its demise would take 700 years to reach us. But if its sudden dimming does suggest the red giant is going the way of the supernova, Earthlings still get treated to a spectacular light show — even if it's not exactly a "live" event.

What's more, the shock wave, radiation and celestial debris from Betelgeuse's passing wouldn't reach our solar system's doorstep for about 6 million years, according to National Geographic. And our ever-protective sun would hold up an umbrella, to make sure Earth doesn't get rained with star innards — leaving humans to bask safely in the cosmic pyrotechnics.

"It would be so incredibly cool!" astronomer Sarafina Nance, who was not involved with the research, tells National Geographic. "By far and away the most incredible thing to happen in my life."

Editor's note: This story has been updated since it was first published in December 2019.

What's eating Betelgeuse?
Betelgeuse is dimming so fast, astronomers say it may be primed to explode.