A 'blue moon' is the name given to the second full moon appearing in a single month. This phenomenon occurs every two and a half years when a solar year includes 13 full moons. As this does not occur monthly like a full moon, the expression 'once in a blue moon' is used to refer to an event that occurs infrequently.
What does a Blue Moon look like?
In December 2009, the first full moon occurred on 2nd and the second on 31st December. [Photos on left are from the second 'Blue' Moon which was also a by coincidence a partial eclipse.]
Can the Moon be Blue?
A 'blue moon' is not actually blue. However, at any time of the lunar cycle when there is smoke or volcanic dust in the atmosphere, the Moon can appear to have a bluish hue when viewed from Earth.
Is a Blue Moon significant to Astrologers or Astronomers?
The 'Blue Moon' phenomenon is based on the western calendar with a year divided into 12 months. As this is a human construct, it holds no significance to astrologers or astronomers. It is possible that an astrologer may consider 13 Full (or indeed 13 New Moons) within a Solar Year to be significant
