U Aquarii belongs to the RCB class of stars. R Coronae Borealis stars (RCBs) are a small group of hydrogen poor, carbon rich supergiants that decline in brightness unpredictably and rapidly by up to 9 magnitudes, and remain at or near minimum light for several weeks or months, even years in some cases. It is generally accepted that the declines are the result of the formation of a cloud of carbon soot that obscures the stellar photosphere, and that this condensation takes place in matter that has been ejected from the stellar surface toward the observer.
The AAVSO data for U Aqr stretches all the way back to 1905. The long-term nature of U Aquarii’s behavior seems to change each decade. From 1976 to 1986 it had 4 or five fadings, then from 1986 to 1998, it remained more or less at maximum except for a couple seasons where it averaged one magnitude fainter than maximum light. Then, in 1999, it faded to fainter levels than ever seen before and has had a decade of fitful recovery to maximum light. Only recently, it has faded again this time fainter than ever recorded before. This is a perfect star for amateur long-term monitoring. Only decades long data will adequately tell this star's story as it unfolds.