Is Weird July 2011 Calendar a Once-in-a-Lifetime Phenomenon?

View full size image

I woke up today quite excited for the weekend. After all, I had read in various email chains and blogs that this Friday, Saturday and Sunday would be like none other in the past eight centuries.

Unfortunately, email chains, much like Nigerian princes who would like to give you $5 million, are not to be trusted.

The claim goes like this. This July is special because it includes five Fridays, five Saturdays and five Sundays. So special, in fact, that this is the first time such a calendar event has occurred in 823 years. Wow! Not quite as cool Halley's comet, but still.

It turns out, though, that it is quite common for the days to line up like this. Every 31-day month has three days that are marked five times each. All it takes for that trio to be Friday, Saturday and Sunday is for Friday to fall on the first of the month. As you might suspect, this can happen several times a year.

Ok, still, maybe there's something special about July, and there hasn't been a July 1 on a Friday in 823 years? Nope. A quick consultation of my iCal shows that July 1 fell on a Friday in 2005, and will again in 2016. Like July 2011, both of those months had five Fridays, five Saturdays and five Sundays. Here is proof:

Leap years make projecting when the five Friday, Saturday, Sunday July sequence will happen again, but there is a pattern: It will happen again in five years, then six years after that, then 11 years after that, and six years after that. That sequence should repeat itself on and on.

Just further evidence that email chains will almost always disappoint.

• 10 Weird Things People Do Every Day (and Why )
• The Numbers Speak: Is 13 Really Unlucky?
• Why Does the New Year Start on January 1?

Follow Life's Little Mysteries on Twitter @llmysteries, then join us on Facebook.