1. Dates College of Alameda pmcdermott@peralta.edu Copyright © 2008 Patrick McDermott Astronomical Julian Day January 1, 4713 B. C. E. Greenwich noon Gregorian Reform Thursday, 4 October 1582 was followed by Friday, October 15, 1582 England Catches Up Wednesday, 2 September 1752 was followed by Thursday, 14 September 1752 Greece Modernizes Wednesday, 15 February 1923 was followed by Thursday, 1 March 1923 Russia Relents Wednesday, 31 January 1918 was followed by Thursday, 14 February 1918

2. 3 Ways to Store Dates Gregorian  Pope Gregory XIII Month Day, Year YY/MM/DD  Sorts chronologically Julian  Julius Caesar Year, Day of Year YYddd –2013-001 is 1/1/2013 Lilian The Access Way  Aloysius Lilius ± some arbitrary date January 1, 1900 = 1 –0.5 is Noon, 0.25 6:00 –36,525 is 12/31/1999  Subtractions work  Sorts chronologically Excel is the Same Unix (1970), Astro:

3. Date Data Entry Calendar magically appears when needed!