Yeah you are right. Or simply gone to nasa.gov: http://science.nasa.gov/headlines/y2009/29dec_bluemoon.htm http://science.nasa.gov/headlines/y2009/29dec_bluem

Yeah you are right. Or simply gone to nasa.gov: http://science.nasa.gov/headlines/y2009/29dec_bluemoon.htm http://science.nasa.gov/headlines/y2009/29dec_bluemoon.htm "The modern definition sprang up in the 1940s. In those days, the Farmer's Almanac of Maine offered a definition of Blue Moon so convoluted that even professional astronomers struggled to understand it. It involved factors such as the ecclesiastical dates of Easter and Lent, and the timing of seasons according to the dynamical mean sun. Aiming to explain blue moons to the layman, Sky & Telescope published an article in 1946 entitled "Once in a Blue Moon." The author James Hugh Pruett cited the 1937 Maine almanac and opined that the "second [full moon] in a month, so I interpret it, is called Blue Moon."