An overview of solar and lunar calendars, their history and lore. Also, of the day and the month, and their relations to the rotation period of the Earth and the orbital period of the Moon. ... This lesson plan supplements: "The Calendar," section #6: on disk Scalend.htm , on the web . ... Terms: solar day, star day (sidereal day), solar year, Julian calendar, leap year, Gregorian calendar, true (sidereal) and apparent (synodic) period of the Moon, Metonic calendar, Moslem calendar. ...