Saturday, September 1, 2012

A new month

And a beautiful full moon yesterday, the second of the month, of course.  Blue moons are nothing like as rare as people think: this occurs every two or three years on average.  Heuristically, for any given month, the first full moon is equally likely to be on any one of the first 29 or 30 days, so we'd expect blue moons about every 30 months.  It's complicated slightly by the shorter and longer lengths of various months, but it's pretty easy to compute.
An older definition of a blue moon,apparently, was the fourth full moon in a season.  Watch for the next time this happens with the full moon on September 19th 2013!

Yours, rarely,

1 comment:

MikeDG said...

One of the things I find fascinating is to look at the night sky and try to work out what it was that ancient men saw and what and how they worked out from what they saw