Family Tree - Warning This One Is Tough!!

[kuiperbelt]

Emily was compiling her family tree and was determined to find out when her great, great grandmother was born. She had managed to recover a letter written by her great, great, great grandfather to his pregnant wife. (Emily's great, great, great grandmother). Although the ink was smudged in places, most of it was legible. It reads as follows:

Dear Morag,

When I set off to work this Monday morning, I had no idea that by the evening we would have a beautiful baby girl. And on our wedding anniversary too! I can recall our wonderful weekend wedding day, J*** 18th, 18***, when we took our vows to create a family together, and, well, here we are!

Happy eighth anniversary on this momentous day, my darling wife.

All my Love, Archie

Important to Note: The number of asterisks does not reflect the number of smudged characters.

When was Emily's great, great grandmother born?

Hint: Doomsday Rule

https://en.wikipedia.org/wiki/Doomsday_rule

[kuiperbelt]

Forgot to add, please provide an explanation with your answer :-)

[ZebuSanctuary]

By application of the Doomsday Rule, a period of 8 years would normally cover 6 non-leap years and 2 leap years.

Therefore any given day/date 8 years ago eg. Tuesday 7th May, would be advanced by 10 days 8 years later. Thus 7th May would now appear on the calendar as a Friday.

If the gt. gt. gt. grandfather was married on Saturday, 8 years later his anniversary would fall on a Tuesday (advancement of 10 days).
Similarly, had he wedded the gt. gt. gt. grandmother on the Sunday, 8 years on, the anniversary would now be on Wednesday.

Clearly this is not the case, since 8 years from the wedding day, the 8th anniversary is now on a Monday (day his daughter was born).

Logic dictates the passing of 8 years can only encompass 7 non-leap years and 1 leap year. This equates to an advancement of 9 days.

The above scenario can only occur if he tied the knot in the year 1800, because 1800 was not a leap year.

Furthermore the letter had to be written before February 28th so that the 8 year window did not incorporate the 1808 leap year.

Conclusion; The letter was written on Monday January 18th in the year 1808 which coincides with the 8th anniversary and Emily's great, great grandmother's birth date.

p.s. An acknowledgement to the genius of Mr Conway.

Thanks to him I can now calculate the day of any given date between the year 1700 and 2099 in a few seconds :-)