Calendar on the wall

Lynn Poole discusses the history of and variety of calendars, including Edmund Osborne's scenic calendars, Benjamin Franklin's "Poor Richard's Almanac", the evolution of calendar girls from 1899 to present, the perpetual calendar, Stonehenge as a calendar, and a deck of cards representing a calendar. He also explains how primitive man reckoned time, the Babylonian astrologers' influence, and the origins of sennight and fortnight. Words for the days of the week in French, Italian, and Anglo-Saxon reflect their origins in the Romans' naming of days for the moon, Mars, Mercury, Jupiter, Venus, Saturn, and the sun. Years can be considered as anomalistic, tropical, or sidereal. The tropical year is explained with a globe and photographer's lamp as the earth orbits around the sun from vernal equinox to vernal equinox every 365.2422 days, requiring a leap year day to catch up. Calendars based on the moon are soon out of sync with the seasons as they're based on the 29.5-day lunar month, which is why the dates of Passover and Easter fluctuate. Mr. Poole displays an American Indian lunar calendar drawn on buckskin for the period 1865-1892. Julius Caesar abandoned the lunar calendar and decreed that the year would run from vernal equinox to vernal equinox; however, by 1582 this Julian calendar was off by ten days, and Pope Gregory decreed the Gregorian calendar, still used today.