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 … or so it seemed … it fell a magnitude short and then faded again !
Another recovery started during the spring of 2016, reaching binocular visibility during the autumn. The brightening seemed to pause in early 2017, but by the late spring it was slowly brightening again.
Most fades of R CrB, however, have been much shorter than the one that started in 2007. Typically they have lasted 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 when R CrB drops below the brightness of comparison J :