1995A&A...295....1L

All data in the B band for BL Lac object ON 231 have been compiled into a light curve from twenty-six publications, dating back to 1892; 560 values are available. The light curve shows that ON 231 is very active and exhibits very complicated non-sinusoidal variations. The light curve probably consists of three kinds of behaviours. The first may be non-periodic or with a period at least longer than the duration of historical observations. In this case, the source seems to maintain two states of intensities, changing in mean behaviour from a bright level with about mean B magnitude 15.45 to a faint level with about 16.45mag between 1969 and 1972. After detailed Jurkevich V²_m test analysis, we found that the second is periodic, with a period of 13.6±1.3years (or 26.6±0.8years) with outburst structure of one magnitude with total width of about 6years. The third one is sporadic, superposing on the previous two behaviors. the periods of 0.981±0.005years (or 2.02, 3.01, ... years) and of a few days are not significant and may be spurious.