Skip Navigation

Mathematical Anniversaries

Updated, 18th March 2012!

This tool has moved to its own domain, at!

What is this?

My wife, as is traditional among married folk, celebrates the number of times our Pale Blue Dot has whizzed around our Bright Yellow Dot since we got married, back on the 22nd April 2006. These are known as anniversaries (from the latin for "return yearly"), and are typically excuses to celebrate events that occurred in the past on the same day of the year as the original events.

People, it seems, are suckers for an anniversary. We celebrate the anniversaries of our own births. We celebrate the anniversaries of the births of our friends and families. Some of us celebrate the anniversaries of the births or deaths of people we've never met. Some of us even celebrate the anniversary of the passing of an entirely arbitrary point in space.

Say what you like, we're big on tradition on this little rock.

Men tend to suffer under this harsh regime of date management. While both we and the fairer sex are obliged to remember all of these days and events, it seems it is usually men who more easily forget them (though it is all much easier since the invention of synchronised online calendars). Not only do we have to remember them, but we are encouraged to buy cards and gifts for people to help them celebrate. It seems it is never enough just to remember - you must provide evidence of your remembering.

This practice of celebrating the number of orbits a marriage has lasted or a person has lived has always seemed a little arbitrary to me. Why hang your hat on that particular astronomical curiosity? Why put special emphasis on multiples of ten of these particular planetary pirouettes? Why not celebrate other milestones?

I feel it is only fair to warn you that things may get a little geeky from this point onwards.

The most astute of you may have calculated by now that the 22nd April 2006 was exactly 1,235 days ago, making yesterday 1,234 days since my wedding. Well done to you. This is, I hope you will agree, a Major Event. It is 3.38 times rarer than the traditional annual anniversary. Our pi-versary (every 3142 days), due in a few years, is far rarer - a pi-versary happens just once every 8.6 years.

I celebrated this latest occasion by buying my wife a 1,234th anniversary card. Similarly, 235 days ago I bought her a 1,000th anniversary card. She, sadly, forgot both of these landmark anniversaries. This may prove useful, should I falter with a later anniversary myself.

By no means are these mathematical anniversaries limited to those specific numbers, or wedding anniversaries, or even days or years passing. My 12,345th birthday will be on the 29th April 2014. My 50th wedding lunar-versary is going to be the 16th January 2010. The list of opportunities to celebrate (or to be offended at friends and families for missing anniversaries, if you prefer) is nearly endless.

Maths and physics, indeed, are full of interesting numbers, sequences and constants. Pi, e, the square root of 2, the golden ratio, square numbers and higher powers, the Fibonacci sequence, the gravitational constant ... all worthy of celebration.

It would be silly to expect you to calculate these anniversaries manually. Therefore I have created a tool to aid you. Please enter the date you wish to commemorate, and click the button to generate a list - extensive but by no means complete - of significant dates to celebrate. The list will be shown on the next page, and you will be able to download the events to your chosen calendar if you like.