Next, I’m going to introduce to the reader an amazing trick called the calendar formula. If used correctly, one can correctly determine the day of the week anything occurred or will occur on. Let’s take February 12, 1809.
Your right! That was the birthday of Abe Lincoln and Charles Darwin. When I used the calendar formula, I found they were both born on Sunday. But, that means nothing if we don’t know how to calculate it. I will assume the reader doesn’t know the calendar formula, so I’ll break it down. The calendar formula is day of month + year over 4 + year + month factor + leap year (If necessary) + century factor all over seven.
The day of the month is the 12th. To that, add that same year and divide by 4. 9/4 is 2 with a remainder of 1. Drop the remainder so 12 and 2 makes 14. Add the year. 12 + 2 + 9=23.
But what’s the month factor? Since the reader probably doesn’t know I will help them. January is 1, February is 4… what? January is thought of as the 1ST month, so its factor is 1. February is the COLD season. September is back to SCHOOL, so its factor is 6. Try and find the rest of the month factors I purposely left out.
Is 1809 a leap year? The answer is no. However if it were a leap year, you would take the month factor for January and February and subtract 1.) The century factor for the 19th Century is 2, for the 18th Century 3, et al. 12+ 2+9+4(forgot to add) plus 2 and you have 29 for an answer. Divide by seven and you get 4 with a remainder of 1. A remainder of 1 would be Sunday……….
Saturday would be 0, so they were born on a Sunday. Once the reader correctly figures out the 12 months and there month factor they can come up with a pneumonic to help them memorize that. I hope the reader will develop some time to figuring out the calendar formula.