For those waiting and watching for the “predicted outburst” of recurrent novae star, T Corona Borealis, the excitement is building. This outburst could occur at any time, but no one knows when. However, the star is showing fluctuations and a magnitude dip which indicates the event is getting close.

The last outbreak was February 1946

A great personal project for the amateur astronomer: I’m using my iPhone 14 and taking a photo every clear night. And when the outburst occusrs, I’ll have a photo of “the appearance” of a new star! It could be as bright as Alpha Corona Borealis (Alphecca) which is ~2.2 magnitude. I’m also visually observing the star with a telescope.

The following image (May 11th 2025) by Mario Motta of Massachusetts, using a 6-inch f/7.6 refractor. North is up and west to the right, with an approximate 1º field, which matches the AAVSO chart. T CrB is the ~10th magnitude star located in the center and presented very nicely while it’s still asleep. If you are following T CrB, and awaiting the outburst: Roger Ivester (May 14th 2025)

June 11th 2025 @ 10:56 PM: (Hazy conditions and a full moon)

Thursday May 23rd @ 11:04 PM

Sunday May 18th @ 9:52 PM

I took the following photo using an iPhone 14 with a 3-second exposure on Wednesday May 7th at 10:00 PM with a moon illumination of 79%

Tuesday May 5th 2025 @ 12:09 AM with a 61% illuminated moon. I plan to post and maintain “a few of my latest photos” of Corona Borealis via this site. However, I will maintain a photo file on all for future reference.

Remember and again: The last outbreak was February 9th 1946, and renowned variable star observer, Leslie Peltier missed it due to an illness, and his observation was to begin at 2:30 AM.

I’m Using the R CrB chart below…just for the primary constellation magnitude star listings.

The following excerpts are from a Sky & Telescope online article.

Take T Coronae Borealis (T CrB). It’s one of only about 10 stars in the entire sky classified as a recurrent nova, with two recorded outbursts to its name. Normally, the star slumbers at 10th magnitude, but on May 12, 1866, it hit the roof, reaching magnitude +2.0 and outshining every star in Corona Borealis before quickly fading back to obscurity. Eighty years later, on February 9, 1946, it sprang back to life, topping out at magnitude +3.0.

Many variable star observers include it in their nightly runs because it’s easy to find 1° south-southeast of Epsilon (ε) in Corona Borealis and only requires a 3-inch telescope. Not to mention the huge payoff should you happen catch the star during one of its rare explosions. Famed comet hunter and variable star observer Leslie Peltier faithfully kept an eye on T CrB for over 25 years, hoping to catch it in outburst. On that fateful February morning in 1946 he’d set his alarm clock for 2:30 a.m., planning to check in on several favorite stars before dawn. But when he awoke and looked out the window, he felt a cold coming on and allowed himself instead to go back to bed. Big mistake. That very morning, T CrB came back to life.

In his book Starlight Nights, Peltier writes:

“I alone am to blame for being remiss in my duties, 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 any more.”

T stayed under the radar for the next 69 years, holding steady around magnitude +10.2–10.3. That began to change in February 2015, when it inched up to +10.0 and remained there until early February this year. That’s when things kicked into high gear with the star steadily growing brighter from late winter through early spring to reach its current magnitude of ~9.2.

Alongside the brightening trend, T’s become bluer as well. Astronomers describe its recent unprecedented activity as a star entering a “super active” state. This last happened in 1938, eight years before its last great outburst.

T CrB followers can’t help but wonder if the next night we look up, Corona Borealis will twinkle with “new” second-magnitude star.

Recurrent novae are similar to nova and dwarf nova types but with unique characteristics that set them apart. All three types occur in close binary stars and involve mass transfer from a normal star to a small but gravitationally powerful white dwarf. Classical novae have only been seen in outburst once and typically brighten by 8-15 magnitudes before slowly fading back to their pre-outburst brightness. Dwarf novae outburst frequently — every 10-1,000 days — with moderate increases of 2-6 magnitudes. Recurrent novae fall in between and typically vary by 4-9 magnitudes over a 10-100 year period.

T CrB has two components: a red giant star in a close, 227-day orbit with a planet-sized white dwarf. Material spills from the giant and accumulates in an accretion disk around the dwarf. Some of that gas gets funneled down to the dwarf’s surface, becomes compacted and heated, and eventually ignites in a spectacular thermonuclear explosion. We see the results as a sudden brightening of the star.

It’s even theoretically possible for enough matter to accumulate on the dwarf to push it past the 1.4 solar mass Chandrasekhar Limit, forcing the entire star to burn explosively as a Type Ia supernova. At T CrB’s 2,500 light-year distance, it would easily cast shadows!

Maybe we’ll have to wait until 2026 (80 years after the 1946 eruption) for T’s next upheaval. Or maybe not. Either way, let Leslie Peltier’s story serve as a cautionary tale. Keep a close eye on this star every clear night, and expect surprises.  Source S&T Magazine.