Great White Spots on Saturn: current and historical observations

Abstract

The bright spot in Saturn's North Tropical Zone which developed in 2010 December prompted the writer to collect together some rare and unpublished observations of previous Great White Spots (GWS) on the planet. As illustrated by series of observations in 1876, 1933 and 1990, and for 1903 and 1960, these GWS show a tendency to recur at intervals of 57 years, twice the orbital period of Saturn. An apparently overlooked (but unconfirmed) GWS observation from 1953 is reported here, which must surely have been a precursor of the 2010 event. It is considered that there may still be many other interesting observations of the planet hidden in forgotten periodicals and archives.