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The Night Sky Will Soon Get ‘a New Star.’ Here’s How to See It.

If you keep a close eye on the night sky in the weeks and months ahead, you may spot something new. It will shine as bright as Polaris, the North Star, for no longer than a week before fading back into darkness.

This ephemeral lighthouse is T Coronae Borealis, often referred to as T CrB. It is a nova, a nuclear explosion bursting forth from the pallid corpse of a long-dead star. Some people might have seen it before — the same beguiling sight lit up our heavens almost 80 years ago — and future generations may see it in another 80 years.

To any world nearby, a nova would be apocalyptic. But to stargazers in our world, some 3,000 light-years away, it “is a fun and exciting upcoming cataclysm,” said Bradley Schaefer, an astrophysicist at Louisiana State University.

Here is everything you need to know about this event: what it is, when it will appear and where to glimpse it.

There are more than 400 known novas in the Milky Way galaxy. They result from the explosive pairing between a normal type of star — for example, a main sequence furnace like Earth’s sun or an elephantine red giant — and a white dwarf, a smoldering stellar core left behind after a star’s demise. The two are gravitationally bound companions destined to unleash a fiery blast into the cosmos.

White dwarfs are relatively small, but they are also so dense that their intense gravitational pulls steal hydrogen-rich matter from a nearby regular star. That volatile material tumbles onto the surface of the white dwarf and, begins to pile up after a while, squashing the lower layers and raising their temperature.

Eventually, that compressed matter “gets past the kindling temperature of hydrogen,” Dr. Schaefer said. It ignites, raising the temperature of the accreted material even further. Past a certain point, a runaway nuclear reaction begins, setting off an apocalyptic blast.

“These novae are basically hydrogen bombs,” Dr. Schaefer said.

But don’t confuse a nova with its more violent sibling, the supernova, which permanently destroys a star and angrily casts off its outer layers. After a nova’s nuclear embers dim, the cycle starts anew, with the white dwarf once again gorging its way toward another explosion.

T CrB is a nova that results when a white dwarf peels off enough of the outer layers of a red giant star that is about 74 times the size of our sun.

The nova last exploded in 1946. Astronomers also observed it erupting in 1866, and historical reports show that it was spotted in 1787 and 1217.

Most novas have explosive cycles that last many millenniums. But T CrB is impatient — a voracious consumer of its red giant’s stellar fuel. Past observations indicate that it erupts once every 80 years, which makes it a recurrent nova — one that flares up at least once per century.

Previous observations of T CrB have also shown that the nova blazes and convulses in a particularly erratic manner in the years leading up to an eruption, and things appear to be no different this time around: Its activity over the past decade or so suggests it is gearing up for an imminent explosion, one that will take place anytime between now and September.

T CrB will appear in the Corona Borealis constellation, which is bordered by Hercules and Bootes. When it “blows its stack, it’ll be as bright as the North Star and it will be visible for a few days,” said Bill Cooke, the Meteoroid Environments Office lead at NASA’s Marshall Space Flight Center in Huntsville, Ala.

“You’re going to notice a new star in the sky,” he added, viewable with the unaided eye.

Don’t miss it. “It’s a once-in-a-lifetime occurrence,” Dr. Cooke said. “How often can people say that they’ve seen a star explode?”

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