Once in a Blue Moon ... is a common way of saying not very often, but what exactly is a Blue Moon? ... On average, there will be 41 months that have two Full Moons in every century, so you could say that once in a Blue Moon actually means once every two-and-a-half years.
www.obliquity.com/astro/bluemoon.html www.obliquity.com/astro/bluemoon.html
We've used Blue Moon to mean the second Full Moon in a single calendar month. ... We have calculated the dates of this type of Blue Moon for the 20th and 21st centuries and put them in a list for you to browse.
www.obliquity.com/astro/blue-st.html www.obliquity.com/astro/blue-st.html
Once in a Blue Moon ... The rare phenomenon of two blue moons (using the more recent definitition) occurring in the same year happens approximately once every 19 years. 1999 was the last time a blue moon appeared twice, in January and March.
www.infoplease.com/spot/bluemoon1.html www.infoplease.com/spot/bluemoon1.html
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Thu, 12/31/2009, 8:00 PM  ·  Travis County Expo Center · Austin, TX
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Once in a blue moon - the meaning and origin of this phrase. ... According to popular usage, a blue moon refers to the second full moon that occurs in any calendar month. On average, there will be 41 months that have two full moons in every century. By that calculation 'once in a blue moon' means once every two-and-a-half years.
www.phrases.org.uk/meanings/269500.html
Blue moon - Wikipedia, the free encyclopedia
A blue moon is a full moon that is not timed to the regular monthly pattern. Most years have twelve full moons which occur approximately monthly, but in addition to those twelve full lunar cycles, e...
en.wikipedia.org/wiki/Blue_moon
In 1999 'Blue Moon' means 'more often than not.' ... February 26, 1999: We've all heard the saying "it happens only once in a blue moon," generally used to describe an uncommon occurance. But for the first quarter of 1999, using the phrase "once in a blue moon" could also mean "two out of three times." ;
science.nasa.gov/newhome/headlines/ast26feb99_1.htm
NASA Science News: subtitle ... July 7, 2004: When you hear someone say "Once in a Blue Moon…" you know what they mean: Rare. Seldom. Maybe even absurd. After all, when was the last time you saw the moon turn blue?
science.nasa.gov/headlines/y2004/07jul_bluemoon.htm science.nasa.gov/headlines/y2004/07jul_bluemoon.htm
Here are some of the ways the expression "Blue Moon' has been used in the past. But, surprisingly, the meaning most used today has come into general use only during the last few years. Most of what follows is paraphrased from 'Once in a Blue Moon' by Philip Hiscock, Sky and Telescope, March 1999, page 53.
home.att.net/~harris83/page5.html
From the Middle Ages to the game of Trivial Pursuit, a folk-lorist explores the meaning of ... "According to old folklore," some people say, the second full Moon in a calendar month is called a "blue Moon." They go on to explain that this is the origin of the expression "once in a blue Moon." But it isn't true!
www.skyandtelescope.com/observing/objects/moon/3305141.... www.skyandtelescope.com/observing/objects/moon/3305141.html?page=1&c=y