The secret of the method is to have a way of knowing the day of the week for one day in each month of the year. Conway's method uses the fact that the following dates always fall on the same day of the week in any given year. They are easy to memorize, and once one has this down pat, some simple calculations allow you to do this for any year. These are the dates that always fall on the same day of the week.
This year, this special day of the week, which Conway calls "Doomsday," is a Friday.
4/4, 6/6, 8/8, 10/10 and 12/12 always fall on the same day of the week (Doomsday) in any year.
If you memorize the phrase "I went to my nine-to-five job at the seven-eleven," you can also remember easily that 5/9, 9/5, 7/11 and 11/7 also fall on Doomsday.
Also, 3/0 (the zeroth day of March, i.e, the last day of February) falls on Doomsday.
January and February are complicated by the existence of Leap Years. In ordinary years, 2/0 (the last day of January) also falls on Doomsday, as does 1/3; in Leap Years, 2/1 and 1/4 fall on Doomsday.
In 1997, which is not a leap year, therefore, the following dates fall on Doomsday (Friday): 1/3, 2/0 (1/31), 3/0 (2/28), 4/4, 5/9, 6/6, 7/11, 8/8, 9/5, 10/10, 11/7 and 12/12.
So, when is Christmas this year? If 12/12 is a Friday, then so are 12/19 and 12/26, so 12/25 has to be a Thursday.
When is Valentine's day? Since this is a not leap year, 2/0, 2/7 and 2/14 are Fridays. So, Valentine's day (2/14) also falls on a Friday.
On what date does Labor Day fall this year? Labor Day is the first Monday in September. If 9/5 is a Friday, then 9/1 is a Monday, and this must be Labor Day.
Practice: On what date does Thanksgiving fall this year? Thanksgiving is the fourth Thursday of November. You figure it out, then check with a calendar to see if you were right.
Practice: On what day of the week were you born? Calculate it, and check with a calendar (or with your parents). Did you get it right?
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