Institute for Dynamic Educational Advancement
Web Exhibits: Calendars Through the Ages: Announcing the Sky
Well-organized website depicts the "Fascinating history of the human endeavor to organize our lives in accordance with the sun and stars." Gives an overview and specifics of the basis of calendars through the ages.
Other
Timekeepers.org: Calendar History
Scroll down this page to see the various topics addressed on this website. Learn a "brief history of the Western Calendar" as well as information about the ancient calendars of the world, including the Sumerian, Egyptian, and Greek...
Other
Western Washington University: Leap Year
It takes the entire page but by the end of it, you will understand the whys and whens of Leap Year Day.