Wednesday, 2 October 2013

Longer months

On October 1, I reviewed the images pinned to my mental calendar for the 1st day of each month since January 2011. I start the review before the date I began this process of remembering every day that passes (17 December 2011) partly because I am trying to fill in the blanks for 2011 and partly because the contrast between finding blanks and finding every day remembered helps to motivate me to continue.

When I do these reviews, I have a sense of the days surrounding the one I remember from the image. It struck me when I recalled February 1 that it had been a while since I had revisited January 31. The reason is simply because September has only 30 days, so I had missed reviewing the 31st day of each month.

I repeated the review since January 2011 recalling the images for the 31st of each month. Obviously 5 months do not have 31 days.

This threw up an interesting mathematical pattern.

I orientate myself through the days of the week by counting on the days over 28 in a month. Here's why. When February has 28 days, the corresponding dates in March fall on the same day. The dates in other months are shifted by the number of days over 28. So December 31, 2011 was a Saturday. Therefore, January 31, 2012 was three days later: a Tuesday.

There was no February 31, 2012, but if there had been it would have fallen three days later again: a Friday. As February had 29 days in 2012, March 31, 2012, would be one day later: Saturday. And, in fact, it was. I instantly know because I remember it was the day we drove home from my parents house with my nephew, to be collected by my brother the following day.

Initially it was a surprise to me that the pattern worked when stepping through non-existent days. But it holds true and makes jumping to the next month straightforward.

There was no April 31, 2012, but if there had been it would have fallen three days later in the week: Tuesday. As April has 30 days, May 31, 2012, would be two days later: Thursday. Which it was. I remember it well. I made a special trip to a shopping mall in the capital.

Unpack what is happening with the numbers and it makes sense why this works.

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