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There was a time when R Coronae Borealis would behave in the way described in astronomy texts. It would spend most of its time near maximum (around mag 6.0) but then, at times that were unpredictable in advance, it would fade dramatically. Sometimes it would fade by a few magnitudes; sometimes it would fall all the way down to 15th magnitude. Then, after an interval of between a few months and a year, it would return back to maximum.
Since it faded during the summer of 2007, however, R CrB hasn't followed these "rules". It stayed faint, mostly around 15th magnitude, for a long time. For most of this time it was well below binocular visibility. There were some short-lived rises in brightness, but it wasn't until the autumn of 2014 that R CrB finally became visible in binoculars again. Everyone expected that it would be back at maximum again by the spring of 2015.
However, the brightening then slowed and, after R CrB had reached about mag 7.0 in late February, a fade set in.
This was no dramatic fade, however.
R CrB has been fading - but only very slowly - as can be seen in this light curve, which is based on observations made by Matthew Barrett and Tony Markham.
The fades occur when R CrB ejects a cloud of material that is rich in carbon ('soot'). This obscures our view of the star and so it appears to fade. When this cloud disperses, we see R CrB brighten again.
What will R CrB do next? Will the slow fade continue or will it accelerate? Will the fade peter out and reverse ? The only way we will know is by observing R CrB.
You can follow the brightness changes in R CrB using the two charts which follow.
The first shows the general location of R CrB. The fade has recently taken R CrB below the brightness of the faintest of the comparison stars labelled on this chart.
The second shows the area around R CrB in more detail and labels a number of fainter comparison stars. R CrB is currently fainter than comparisons G and J. Recent reports place it between comparisons K and L in brightness.
Added by: Tracie Heywood