The Sky This Week, 2012 August 27 – September 4 — Naval Oceanography Portal

The month’s second Full Moon occurs on August 31st at 9:58 am Eastern Daylight Time. The second Full Moon to fall in a calendar month has now become popularly known as a "Blue Moon", although skylore experts don’t necessarily agree on this. The term initially referred to the third Full Moon in a season with four Full Moons (normally there are three.) However, a misinterpretation of the 1937 "Maine Farmer’s Almanac" in a popular magazine in 1946 led to the current definition. Either way the event is comparatively rare, occurring seven times in a 19-year cycle. By either definition the "Blue Moon" resets the monthly calendar of popular Full Moon names, so the next one, which will occur on September 29th, will be the fabled "Harvest Moon".

The Sky This Week, 2012 August 27 – September 4 — Naval Oceanography Portal