R Coronae Borealis

Have you ever had a backwards day, when everything seemed to be happening in reverse, and things turned out to be precisely the opposite of what you expected? Such a day should end with your first observation of a “backwards nova,” a star called R Coronae Borealis.

Usually, a nova stays at minimum until the day of its mighty explosion. R Coronae Borealis does the opposite. It stays at maximum, a bright beacon around magnitude 6, and then without warning plunges eight full magnitudes to the depths of a magnitude 14 minimum. At its brightest it can be seen with a good pair of unaided eyes if the sky is dark enough. At minimum it will test the mettle of a 20 cm (8-inch) telescope.

R Coronae Borealis is not really a nova in reverse; it only acts like one, perhaps by surrounding itself at completely irregular intervals with a shell of carbon particles which absorb light. In late February of 1977, I returned from an evening out and the clouded sky was just beginning to clear. I decided to check the sky and observe just one variable for a total session of no more than ten minutes. I thought I would try R Coronae Borealis since the night before and for many months earlier it had been shining brightly at about magnitude 6. It often happens that my shortest observing sessions turn out to be the most productive.