RY Sagittarii is a yellow supergiant and an R Coronae Borealis type variable star in the constellation Sagittarius.

Colonel Ernest Elliott Markwick first came across what became known as RY Sagittarii during searches for variable stars while posted in Gibraltar.

[5] The spectrum was first noted to be peculiar at the time,[6] and by 1953 it was classified as a R Coronae Borealis variable, along with a handful of other stars.

[10] Its light curve has been studied for over a hundred years and is typical for the class, characterised by a sudden drop in brightness of several magnitudes over a few weeks before gradually brightening over the following several months.

[10] The cause of the drop in magnitude is the presence of dust clouds of carbon obscuring (and most likely ejected from) the star, though the mechanism how this might occur is not known.