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U Monocerotis

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.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484