The Month

Phases of the Moon The moon is the second brightest object in the sky. The shape of the moon changes each day. –Waxing light on right –Waning light on left The changes are called phases.

Synodic Month The lunar or synodic month repeats every days. –Named phases: new, first quarter, full, last quarter Wikipedia

Sidereal Month The sidereal month matches the moon to the stars positions. –27.32 days –Shorter like sidereal day Ian Cameron Smith

Ancient Calendar Most early cultures used the day and month to mark a year. –Babylon: 12 months, 6 with 29 days and 6 with 30; Add 13th month occasionally –Egypt: 12 months each with 30 days plus 5 extra days –Polynesia: 13 lunar months, drop 1 month occasionally

Lunar Calendar Many modern cultures use lunar calendars. –Hebrew, Islamic, Han Han Chinese calendar: –Month starts with the day of the rising new moon –Each month will have either 29 or 30 days Each year has 353 to 355 days. –Short by 11 days –Leap month to keep the start of the first month between 1/21 and 2/21 –Leap year 383 or 384 days.