I received the following from by bruv, Freereeder, today, and it seems worthy of airing.

This Saturday (31 July) is a special day --- because it's a blue moon.

It's a relatively rare event that we get two full moons in one calendar month, ie: thirteen full moons in a Gregorian calendar year. That's because the lunar month is 28 days and the calendar month varies between 28 and 31 days.

Where this occurs, the second full moon of the month is called a blue moon. Whether this is actually the origin of the phrase once-in-a-blue-moon is, surprisingly perhaps, a matter of some debate.

The last f/m was on Friday July 2nd, so this Saturday we have a blue moon.

I thought everyone should know about this!