Including Julian, Gregorian, Jewish, Islamic, Chinese, and Mayan. The Encyclopaedia of Calendars. The mathematics of the Chinese calendar. Explains the rules for the Chinese calendar. A list of many American Indian tribe's names for months, days, and other calendar related information.
Islamic months begin at sunset on the day of visual sighting of the lunar crescent.
This site discusses the concept of the International Lunar Date Line and contains numerous maps of crescent visibility. The mathematics of the Islamic calendar in Singapore. Civil time is occasionally adjusted by one second increments called leap seconds. A detailed explanation of what a second actually is, and why leap seconds are necessary. Chinese festivals are listed and the moon phase is displayed.