TCrB chart
Locate the field for recurring nova, T Coronae Borialis. (Glenn LeDrew)

Time for T

A recurring nova in Corona Borealis might be getting ready to blow.

One of my all time favourite astronomy books is Starlight Nights by Leslie Peltier. My copy is well-worn from decades of use, and it occupies a prime spot in my bookcase. I return to the book for inspiration frequently. Few have known the sky as well as Peltier and no one has written about the joys of stargazing more passionately.

Leslie Peltier discovered or co-discovered 12 comets and 6 novas, but he’s best known as a variable-star observer, accumulating more than 132,000 brightness estimates before his passing in 1980. One star that he watched closely is now in prime viewing position and possibly warming up for a once-in-a-lifetime display.

TCrB chart
Use this chart to locate the field of the recurring nova T Coronae Borealis. (Base chart by Glenn LeDrew.)

Our story begins in 1866, when a faint star in Corona Borealis suddenly brightened to 2nd magnitude. For several weeks it was one of the most conspicuous points of light in the region, equalling Alphecca, Alpha (α) Coronae Borealis. Eventually this mysterious sun faded back to 10th magnitude, becoming a telescopic target once more. Subsequent analysis revealed it to be a recurrent nova, which meant that it was likely to repeat this spectacular performance. It’s now known as the Blaze Star and is officially designated T Coronae Borealis (T CrB).

When Leslie Peltier learned of T CrB many years later, he added it to his variable star watch list. For more than 25 years Peltier monitored it closely. In that time he noted occasional minor variations in the star’s light output, but nothing to match the 1866 outburst. “Then, one night in February 1946,” he wrote, “it stirred, slowly, opened its eyes, then quickly threw aside the draperies of its couch, and rose!”

A variable star observer’s dream come true, right? Not quite.

“I had set the alarm for 2:30 a.m. intending to get up and observe some early morning variables,” he recalled. “The alarm clock did its part. I looked out the window and the stars were clear and bright. But apparently I was not, for I sneezed once or twice and got the feeling I was coming down with a cold. So I went back to my warm bed. Thus I missed the night of nights in the life of T Coronae.”

“I alone am to blame for being remiss in my duties,” Peltier concluded sadly. “Nevertheless I still have the feeling that T 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 anymore.”

This detailed chart by the American Association of Variable Star Observers (AAVSO) shows the field surrounding T CrB. The magnitudes of several comparison stars are given with the decimal place omitted. The brightest star plotted is magnitude 4.2 Epsilon (ε). Use this chart to estimate T CrB’s brightness.

Seventy years since its last outburst, T Coronae Borealis has remained quiescent. But that might be about to change. The star has been growing brighter in recent months and has edged up from magnitude 10 to around magnitude 9.2. This mirrors the star’s behaviour leading up to its 1946 outburst. Need I urge you to check out this famous star? Even if you’re just out walking the dog, have a look. After all, you don’t want to miss the celestial event of a lifetime the way Leslie Peltier did!

David A. Rodger is a life-long amateur astronomer and science writer. He views the sky from his townhouse in North Vancouver, British Columbia.