R Coronae Borealis variable

An R Coronae Borealis variable (abbreviated RCB, RCrB) is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation (a few tenths of a magnitude), and one irregular unpredictably sudden fading by 1 to 9 magnitudes. The prototype star R Coronae Borealis was discovered by the English amateur astronomer Edward Pigott in 1795, who first observed the enigmatic fadings of the star. Since then, only about 100 RCB variables have been identified, making this class a very rare kind of star.