The Light Curve of Periodic Comet Wirtanen

The light curve of Periodic Comet Wirtanen has been analyzed for the 1986 and 1991 apparitions, the only two monitored by visual observers, The comet’s light curve displays a rapid rise of the order of five magnitudes between -73 days and -45 days (prior to perihelion). From -45 to (about) +16 days the comet brightens at a rate of approximately 0.022 magnitudes per day. After reaching peak brightness, the comet fades by about 0.031 magnitudes per day. The comet’s intrinsic brightness was 0,5 -0.7 magnitudes fainter during the 1991 apparition than in 1986. There are indications that this comet may have experienced brightness flares of about one magnitude in 1986. Periodic Comet Wirtanen (P/Wirtanen) was discovered photographically as a 17th magnitude object on January 15, 1948 by Carl A. Wirtanen (Lick Observatory, California). As summarized by Kronk (1984), the comet remained faint, never becoming brighter than 15th magnitude, during