Growing up, that phrase seemed like it was my Mom's favorite thing to say:
"They only come to see Us once in a blue moon"
That happens like once in a blue moon"
Etc. Etc. Etc.
Blue moon - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Blue_moon
News about blue moon
http://www.bing.com/news/search?q=blue+moon&FORM=EWRE
The next full moon is happening on my birthday 2012,
which is how often I wish my birthday's came around.
But then you'd be twice as old at each birthday ;D