NASA
Nasa: From Stargazers to Starships: The Calendar
A lesson plan that gives an overview of solar and lunar calendars, their history and lore. Also, of the day and the month, and their relations to the rotational period of the Earth and the orbital period of the Moon.For versions in...
National Geographic
National Geographic: A Reason for the Season
This site provides a learning activity that can be adapted for all age levels that deals with the seasons. Students are asked to become a "season sleuth" and discover what causes the seasons to change.
Khan Academy
Khan Academy: Frontispiece of the Codex Mendoza
The Codex Mendoza, commissioned by Viceroy Mendoza, contained information about the lords of Tenochtitlan, the tribute paid to the Aztecs, and an account of life "from year to year." Read descriptions and view pictures of the codex in...
Other
Livius: Caesar's Calendar Reform
A selection from Plutarch that highlights Caesar's desire to reform the calendar and how he came about with the changes he enforced.