When April 20 is a Tuesday - why is January 17 always on a Monday the following year whether or not the following year is a leap year?

Answer 1

We think of leap years as having a day being skipped. This is true, except that people forget that the skipping only happens after the 29th of February. So days from the 1st of January to the 28th of February in a leap year, will not have skipped the extra day. They will do so in the following year. So it is the days from the 1st of March in a leap year to the 28th of February in the year after a leap year that will be skipped. For example, the question was asked on Saturday the 21st of February 2015. The 21st of February in 2016 will be on a Sunday. The 21st of February 2017 will be on a Tuesday. As the 17th of January doesn't skip the extra day in the leap year, but in the year after, that accounts for your apparent anomaly. It is like that the year runs from the 1st of March to the 28th of February, so the relationship between days in that period, like the 20th of April and 17th of January, remain the same.