Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Eric A. Taylor on 30/12/2009 08:42:41

Title: How rare is a blue moon eclipse?
Post by: Eric A. Taylor on 30/12/2009 08:42:41

I've just read that there will be a lunar eclipse on December 31, 2009. The full moon on this night will be the second in December marking it as a "blue moon". As if it's not rare enough to have a blue moon on New Years Eve our friends in the East will see a lunar eclipse. I wonder how rare a blue moon eclipse is?

Or does this not count because the eclipse in the East will be on January 1,  2010?

I'd still like to know how rare it is.

Title: How rare is a blue moon eclipse?
Post by: Soul Surfer on 31/12/2009 14:30:04

I'm not sure but it is possible to do some quick guesstimating.  The period of a lunation is about 28 days and months are on average between 30 and 31 days say 30.5   so  2.5/30.5 =  .08  months  say 1 in 12 are blue moons.
so it is about 1 in 12 lunar eclipses are "blue"  there are on average 2 lunar eclipses in a year so we should get a blue lunar eclipse about once every six years or so.  However there will be some periodic factors in this that will make the intermittency variable.