ABSTRACT
The Gregorian calendar that is in widespread use today has been devised to match the tropical solar year to a high degree of accuracy. It aims at preventing long-term drift in the dates of the summer and winter solstices and the spring and autumn equinoxes. It can be classified as a purely solar calendar because it makes no attempt to keep in step with the cycles of the Moon. Because it is linked to a particular part of the lunar cycle, the date of Easter changes from year to year. The history of the development of the Gregorian calendar provides insight into some of its quirky features, such as the derivation of the name of the twelfth month from the Latin word for ten. It also explains why the October Revolution occurred in November 1917.
