Happens every... um... lots of years. (5 years and 2250 days ago)
When I took this photo it reminded me of first few lines in the poem The Highway Man by Alfred Noyes:
"The moon was a ghostly galleon tossed upon cloudy seas"
Okay I my imagination has taken some poetic license as there is no sea anywhere but ;)
Loreena McKennit has done a lovely version of the poem set to music http://www.youtube.com/watch?v=S2CFM4ev-g8 or the full poem can be read here:
http://www.potw.org/archive/potw85.html or (5 years and 2247 days ago)