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R Coronae Borealis has been brightening in recent months and is now approaching the brightness range that makes it visible in binoculars.
Historically, R CrB has spent most of its time near mag 6.0, but has been prone to sharp fades that can take it as far down as 15th magnitude. Usually, it then returns back to maximum after a few months. These fades result from the ejection of carbon particles by the star which then (like soot) block out much of the light from the star. R CrB brightens again when this cloud disperses.
The most recent fade has been exceptional. As this BAA VSS light curve shows, a sharp fade started in the early summer of 2007. On this occasion, however, R CrB has stayed faint. There have been a number of partial recoveries, most notably that of autumn and winter 2014-2015, but R CrB has in each case failed to complete its recovery and has faded back to minimum again.
By mid 2016, however, R CrB was starting to brighten again. Observations by SPA VSS member Don Matthews showed R CrB to be at mag 14.1 on May 11. By July 22, however, it had brightened to mag 13.0. The brightening continued, with R CrB reaching mag 11.8 by Sep 5 and mag 10.4 by Oct 5. Don's latest observation on Oct 24 showed R CrB to have reached mag 9.3.
Will this brightening continue all the way to maximum?
Observations posted elsewhere do seem to suggest that the brightening has been slowing in recent weeks.
Is this a temporary slow down, or is R CrB going to fall short of maximum and, as happened in spring 2015, fade back to minimum again?
The only way to find out is to have a look for yourself.
R CrB is located at RA 15h48m34.4s, Dec +28 09 34.
This chart, which is approx 4 degrees by 3 degrees and has north at the top, shows the position of R CrB, along with comparison stars that you can use when estimating its brightness.
In early November, R CrB has been fainter than comparisons L and M, but brighter than comparison KK.
At maximum, R CrB would be brighter than all of the stars shown on the chart.
Unfortunately, we are now at a time of the year when Corona Borealis is already rather low in the western sky at the start of the night. Hence you will need to go out and observe R CrB as soon as it gets dark. If you delay for too long, you may find that R CrB has become "lost" in the haze near the horizon.
Corona Borealis is, however, now also briefly visible low in the north eastern sky just before dawn. It will become better placed in the pre-dawn sky as the weeks pass, so if you can go out and observe at such a time, that gives you another option.
More information about R CrB, including a chart which shows the position of R CrB relative to the brighter stars of Corona Borealis, can be found in this guide
Added by: Tracie Heywood