Revealing Variety of Comets by Long-Term Monitoring Observation with a 50-cm Telescope

We have been monitoring comets using the 50-cm telescope at the Mitaka campus of the National Astronomical Observatory, Japan since 1996. Over 20 comets, including bright ones such as comet C/1995 O1(Hale-Bopp), have been observed over long-term periods, namely over large heliocentric distance scales. Our samples show variety of comets in terms of both morphological and temporal variations. Several typical examples of various morphology, probably due to dust, are shown to emphasize the importance of long-term monitoring of comets.