Every 80 years, this star appears in the sky—see the once-in-a-lifetime phenomenon

A new star is coming to the Northern night sky. It could appear in days, or it could be months—astronomers aren’t sure, despite waiting almost 80 years for it to shine. But once it does, it will burn so bright as to be visible with the naked eye for a week.

And then, as fast as it appeared in the celestial panorama, it will be gone.

The reason for this flashy apparition is T Coronae Borealis (or T CrB, more briefly) which is a rare phenomenon known as a recurrent nova.  As its name suggests, T CrB is located in a horseshoe-shaped constellation called the Corona Borealis, or Northern Crown, about 3,000 light-years from Earth.

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Unlike classical novas created when a star explodes at the end of its life, recurrent novas, as the name suggests, erupt much more frequently, but they are also caused by different stellar processes than a true nova. In T Coronae Borealis’s case, its last eruption occurred in 1946. Only 10 of these repeating novas are known to exist in the Milky Way galaxy.

What causes this cosmic body to erupt?

T Coronae Borealis’ light is not the result of a single cosmic body exploding but instead a celestial dance between two dying stars orbiting one another. The larger of the two, a red giant star with roughly the mass of our solar system’s sun, is losing its material, including hydrogen and helium. Some of this ejecta falls to its companion white dwarf which despite being roughly the size of Earth contains around 40 percent more matter than the sun, making it incredibly dense.

As the white dwarf gobbles up its companion’s waste, its temperature rises and rises and it becomes even more dense. Eventually—every 80 years or so—it hits a critical tipping point, triggering a series of powerful nuclear fusion reactions that makes it erupt.

“We've been following it worldwide and it's been doing some fun things,” says Sumner Starrfield, a professor at Arizona State University who has studied the star system extensively over his career. “It got brighter for a few years and now has faded a bit. It seems to be doing pretty much the same thing it did just before it exploded in 1946, which is why we're suddenly very interested.”

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When will it be visible—and how do you see it?

It’s unclear exactly when the eruption will happen. According to NASA, it could be anytime between now and September, though Starrfield notes that this is a good guess, and it could even be years until we see the explosion in our skies. But when it does happen, it will be a blink-and-you-miss-it opportunity for stargazers.

“The peak of it is very fast,” explains Bradley Schaefer, a professor emeritus at Louisiana State University who is among the leading scholars on T Coronae Borealis. “It's short, it stays at peak brightness only a few hours and starts fading fast and it's faded away from naked eye brightness in just a week.”

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“If you're just Joe Blow Average going outside looking up wanting to see it with your unaided eye, you’ve only got a couple of nights to do it in,” Schaefer adds.

When it does erupt, it will be closely monitored—Starrfield’s team has reserved time on the James Webb Space Telescope to observe the eruption and determine exactly how much mass gets ejected into space in the process.

But some of the most important observations of this rare phenomenon will come from a network of amateur astronomers using their backyard telescopes. Members of the American Association of Variable Star Observers (AAVSO) and the Astronomer’s Telegram have been keeping a close eye on T CrB. In the last few years, a new data point has been uploaded to a central hub, on average, once every 10 minutes, making for a constant stream of updates on how brightly the system is glowing. One of these amateurs will no doubt lay claim to bragging rights of being the first to spot the coming eruption.

“The reason why a lot of people are observing it is people like things that go boom,” says AAVSO Executive Director Brian Kloppenberg. “A lot of amateur astronomers have a strong drive to be the person that discovers something or sees the first event.”

But Schaefer has his own plan in place for the moment he receives the news — and he is determined not to miss it. Ironically, Leslie Peltier, the astronomer who predicted T CrB’s 1946 eruption missed the grand event thanks to an untimely cold. As the eruption takes place, it’s anticipated that T CrB will glow as brightly as the North Star, the brightest point in the famous Little Dipper.

“Certainly, I'm going to go rushing outside the first time it's dark and clear, because I want to have my observations contribute to that light curve,” Schaeffer says. “When you hear about T CrB going up, you don't need a telescope, all you’ve got to do is walk outside on a dark, clear night and look up.”