How Long Will We See The Nova?
To predict the duration of a nova's visibility, astronomers look to its past light curve for guidance. The recurring nova T Coronae Borealis is one of only two such "new" stars known to be visible to the naked eye. Every 80 or so years the faint star system erupts, with the last event occurring in 1946. When it explodes anew as anticipated, observers will have a short window to find clear skies.
In 1946, February opened with the star at visual magnitude equal to 10. The magnitude scale astronomers use is logarithmic, with bright stars being low like V=0 or V=1, stars on the edge of visibility being about V=5 or V=6, and stars requiring optics to be seen in the higher numbers, like V=7 and beyond. A handful of the brightest stars can have a negative visual magnitude like V= -1. So T Coronae Borealis, a binary system with a white dwarf star cannibalizing an adjacent red giant star, resides deep in the darkness during the bulk of its existence.
When the duo's internal dynamic reaches a certain threshold, the star erupts in a massive explosion. After traveling thousands of light years, the emitted light arrives at earth. Meanwhile, a corps of astronomers, professional and amateur alike, are continually monitoring known variable stars in anticipation of some kind of change. On Saturday, February 2, 1946, the pair were observed in its quiescent stage. No observations were recorded on Sunday.
Monday the 4th brought the first hint of an outburst. An observer recorded V=5, which is faint for the naked eye but achievable in a dark sky. That is equivalent to being able to see all seven stars that define Ursa Minor, the Little Dipper. With less light pollution in 1946, it would have been relatively easy to spot if you knew where to look. Unfortunately, the word of a possible outburst did not apparently reach a broad enough audience and T Coronae Borealis (T CrB) went unobserved for five days.
On Saturday the 9th, observations suggested it reached a respectable brightness of V=3. Whether it had peaked at a brighter magnitude in the intervening days is unknown. Eighty years prior T CrB apparently reached a magnitude of V=2, about as bright as Polaris.
Within one day the nova diminished from its peak V=3 down to V=4. If you know where to look under the left bend of the U-shaped constellation Northern Crown, you could likely find a fourth magnitude star under dark skies. From an urban sky it becomes a challenge, but you still have a chance of catching it with your cell phone camera. Nowadays, fifth and sixth magnitude stars can only be found in remote areas with dark skies.
A week after it first appeared, the nova dipped under the magnitude v=6 threshold, which is about the limit of the human eye.
Brian Kloppenborg of the American Association of Variable Star Observers (AAVSO) was among the authors of the paper predicting the appearance of T CrB after it exhibited a "pre-eruption dip" in 2024. He writes on 10 November 2025 in the AAVSO forum Observing Campaign 875: Monitoring T CrB:
To quote Leslie Peltier, “Novae are utterly unpredictable.” T CrB is no different. The reality is that there are significant uncertainties in the physical state of the system, and we can’t predict with a high degree of confidence when the eruption will occur. It could be tonight, next week, next month, or years into the future. For those who’d like to dig deeper into the current understanding of the system, see the recent paper by Munari et al..
Despite our modern desire to stay constantly connected and be instantly notified, I don’t think you’re at any risk of missing the eruption due to a few hours’ delay. Here’s a closer look at the 1946 event:
The first observation at V = 10 was on 1946-02-02, followed by V = 5.1 on 1946-02-04 and a peak at V = 3 on 1946-02-09. The brightening phase, therefore, took a few days—not hours. After the peak, V = 6 was recorded a week later on 1946-02-16, and the system didn’t return to V ≈ 9.6 until a month later on 1946-03-09. While the event was relatively fast by nova standards, a few hours’ delay won’t ruin the show in my opinion.
