You might want to know what day of the week your birthday is this
year. Mathematician John Conway invented an algorithm called the
‘Doomsday Rule’ to determine which day of the week a particular date
falls on. It works by finding the ‘anchor day’ for the year that you’re
working in. For \(2025\), the anchor
day is Friday. Certain days in the calendar always fall on the anchor
day. Some memorable ones are the following:
‘\(0\)’ of March - which is \(29\)th February in a leap year, and \(28\)th February otherwise.
\(4\)th April, \(6\)th June, \(8\)th August, \(10\)th October and \(12\)th December. These are easier to remember as \(4/4\), \(6/6\), \(8/8\), \(10/10\) and \(12/12\).
\(9\)th May, \(11\)th July, \(5\)th September and \(7\)th November. These are easier to see as
\(9/5\), \(11/7\), \(5/9\) and \(7/11\). A mnemonic for them is “9-5 at the
7-11".
Then find the nearest one of these dates to the date that you’re looking
for and find remainders.
For example, \(\pi\) day, (\(14\)th March, which is written \(3/14\) in American date notation. It’s also Albert Einstein’s birthday) is exactly \(14\) days after ‘\(0\)’th March, so is the same day of the week - Friday in \(2025\).
What day of the week will \(25\)th December be in \(2025\)?