1. The Whirligig of Time Astronomy 360

2. Essay 2 Keeping Time The length of the day is set by the earth’s rotation on its axis With some reservations! The Solar Day (not exactly 24 hours) The Sideral Day (23 hr 56 minutes) (Star Time) The Solar Day is 3’ 56” longer than the sidereal day The Earth’s Orbit is not circular The Mean Solar Day (average value of that interval over the year)

3. Keeping Modern Time My 1913 Waltham Pocket Watch My 2003 Remington Pocket Watch (crystal) Modern Watches NIST-F1, the nation's primary time and frequency standard, is a cesium fountain atomic clock developed at the NIST laboratories in Boulder, Colorado.... Time Synchronization with radio signals

4. Calendars of Time Julian Calendar46 BC Gregorian Calendar1582 BC Muslim Calendar(a lunar calendar) Jewish Calendar (also a lunar cycle) Chinese Calendar (a 365.2444 day year)

5. The Gregorian Calendar Leap year corrects by adding a day to the calendar every fourth year Unfortunately the year is actually a little bit shorter than 365 ¼ days. Thus leap year corrects a tiny bit too much Centuries that are not divisible by 400 are not leap years (1900 was not a leap year but 2000 was) (Gregorian calendar)

6. This week’s homework assignment