Four thousand days -- more than a decade -- in the life of R Coronae Borealis. Every few years, sometimes more, sometimes less, sixth magnitude R CrB suddenly plummets in brightness, then more slowly recovers. The events, completely unpredictable, are thought to be caused by ejected puffs of carbon dust that lie in the line of sight and dramatically dim the star. (Courtesy of the American Association of Variable Star Observers.) |