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Guide to R Coronae Borealis

A star that spends most of its time near maximum, but which at times unpredictable in advance will fade dramatically.

Having said that, it did start a fade in the summer on 2007 that turned out to be record breakingly long. It was not finally returning back to maximum until early 2015, but then it faded again ! 

 

 

 

 

 

 

 

 

 

 

 

Most fades, however, are much shorter than this, lasting for a few months or maybe a year or two. Some fades will only go down two or three magnitudes, but others will take it all the way down to 15th magnitude. Sometimes it starts to brighten from a fade, but then drops back down again - R CrB is that unpredictable!

Extreme brightness range 5.8 - 15.0
More typical range 6.1 - 6.4 (until a fade starts ...)
Period of variation None - totally unpredictable
Frequency of observation Worth checking on every clear night
Observe using 40mm or 50mm binoculars will suffice for most of the time, but 50-80mm binoculars will be required during smaller fades and a telescope is required during the deepest fades
Visibility Can be observed all year round, but is rather low in the evening sky in November and December. From late October it is visible in the pre-dawn sky and is only visible in the morning sky from Christmas to the end of January

 

 

 

 

 

 

 

 

 

 

Here is a finder chart (approx 11 degrees x 8 degrees, with north at the top) which will allow you to locate R Coronae Borealis when it is near maximum. You can use the labelled comparison stars to make brightness estimates of R CrB and hence to watch out for the onset of fades.

You will need to use this next chart, which is 4 degrees by 3 degrees, when R CrB drops below the brightness of comparison J :

and if you want to observe R Coronae Borealis during its deepest fades, you will need to use this BAA VSS chart  (which has south at the top)