U Mon is an example of an RV Tauri star -- a pulsating variable showing pulsations with short-term regularity but with long-term irregular variations. U Mon has a pulsation period (the length of time between two minima of equal depth) of around 92 days. However, its long-term light curve shows deep dips in brightness that recur every 2500 days or so. In recent years, these deep fadings have stopped. You can learn more about U Mon by reading our Winter 2003 Variable Star of the Season article.
Prepared By: Matthew Templeton