A 'new' star will light up the sky soon and you can see it for yourself

Star light, star bright, will there be a new star tonight?

That's the question astronomers are waiting to answer, as they await a spectacular stellar explosion they believe is on the horizon.

To be clear, the star already exists, but it's invisible to the unaided eye — for now.

Roughly 3,000 light years away is a binary star system in the constellation Corona Borealis. As its name suggests, a binary star system consists of two stars. In this case, one is a large red giant star, and the other is a small, but incredibly dense white dwarf.

As they orbit each other, the red giant's material gets sloughed off and falls into the white dwarf where it accumulates and heats up. The white dwarf then experiences a thermonuclear explosion — a nova — brightening to a point where we can see it with the unaided eye on Earth. 

(Interestingly, our own sun will eventually become both a red giant and a white dwarf as it nears the end of its life. First it will swell, shedding its outer layers [and yes, destroying all life on Earth], and then become compact and super dense, around the size of Earth.)

In order to get a sense of  just how bright T Cor Bor (as it's known, for short) will get, you need to know how astronomers measure brightness. It's on a magnitude scale, where — counter-intuitively — the lower the number, the brighter the object. 

T Cor Bor normally shines at a magnitude of 10. However, it's believed that it will shine as bright as a second-magnitude star.

When a star changes brightness over time, astronomers call it a variable star. This particular type of variable star is called a recurrent nova. 

But the big question that hangs in the air is: when? When will T Cor Bor experience that magnificent explosion?

Brightening and fading

T Cor Bor was discovered by astronomer John Birmingham in western Ireland when it went nova in 1866.

Before that no one understood what caused the periodic brightening and fading of some stars. 

But the nova occurred again 80 years later, in 1946. Going backward, Brad Schaefer, an astronomer and professor emeritus at Louisiana State University who's been studying T Cor Bor for decades, recently noted a long-lost account of a brightening in the same location in 1787, which suggested that T Cor Bor is a recurrent nova with a period of 79 to 80 years.

Though there have been few eyewitness accounts, Schaefer's work from the 1945-47 data shows a rapid drop in the star's brightness just before the eruption. This is where we are at the moment, leading Schaefer and others to believe we're heading for a rapid brightening any time between now and September.

Once it erupts, you need to be fast to see it at its brightest.

"T Cor Bor goes from its lowest level, which it's just trundling along at right now, to its peak [in about] three hours or something like that — it's really fast," said Schaefer. 

"It's important that we catch it early because the time it stays at peak … it's half a day. It starts fading almost immediately. So it remains near first magnitude or second magnitude, where it's easily visible to the human eye for [about] a day. So you've got a day or two as a chance to see it."

There are only about 10 known recurrent novas, but the others have much longer time scales. T Cor Bor, with its period of 79 to 80 years, is unique. 

"The fact that it's recurring on a timescale we could work with, as far as humans are concerned — not thousands of years… but it's still within a human lifetime — makes it very special," said Paul Delaney, an astronomer and professor emeritus at York University's department of physics and astronomy in Toronto.

The great part about this nova event is that amateurs from around the world will be monitoring it closely, and providing much-needed data.

"You have 24-hour coverage because you have observers scattered all longitudes around Earth," Schaefer said. "And so there are going to be people in Hawaii who are going to be watching it. There are going to be be people in Japan and and even Australia watching it. So so we have full longitude coverage. But you didn't have that back in 1946."

Don't be like Leslie Peltier

Who is Leslie Peltier? Well, one may consider him one of the unluckiest astronomers in the world.

This famous comet-hunter and fan of variable stars had been carefully watching T Cor Bor for roughly 25 years, hoping to catch it at its eruption phase. The story goes that, one morning in February 1946, he set his alarm to wake up at 2:30 a.m. to check on a few stars, including T Cor Bor. But he felt a little under the weather and decided to remain in bed. You can guess what happened: T Cor Bor erupted.

In his book Starlight Nights, he (somewhat bitterly) wrote: "I alone am to blame for being remiss in my duties, nevertheless, I still have the feeling that T [Cor Bor] could have shown me more consideration. We had been friends for many years; on thousands of nights I had watched over it as it slept, and then it arose in my hour of weakness as I nodded at my post. I still am watching it but now it is with a wary eye. There is no warmth between us any more."

So if you hope to have better luck than Peltier, you need to know what you're looking for. The best advice is to familiarize yourself with the constellation ahead of the eruption.

You can find T Cor Bor in the constellation Corona Borealis, hence its name. The constellation's Latin name translates to the "northern crown," as it looks like a crown and is found in the northern sky. 

Corona Borealis looks like a squished "U" in the northern sky between the constellations of Hercules and Boötes (pronounced Boo-OH-teez). You can easily find Boötes by its brightest star, Arcturus. There will be no other nearby star as bright as Arcturus.

Under dark skies you can see Corona Borealis's seven brightest stars. The brightest is Alphecca which is at a magnitude of roughly 2.2. Once T Cor Bor goes nova, it will be almost as bright as Alphecca.

"What I've been doing with my daughter is we're just going out, and we're trying to find the constellation in the sky. And we're just looking at what it looks like now," said Brian Kloppenborg, executive director of the American Association of Variable Star Observers.

"And just asking questions about, you know, what do you what do you see around it like, and then then when the eruption actually occurs, I'll probably ask her: do you see a new jewel on the crown?"

So, familiarize yourself with the night sky and take a peek each night if you can. You may catch that extra crown jewel.