From the Boston NCGR newsletter, September 2004

The Blue Moon
by Pam Ciampi

The familiar expression "once in a blue moon" is generally used to refer to something that happens infrequently or rarely. But there are at least three different explanations for what makes a moon blue. The first explanation is when the physical color of the moon changes from white to blue. This unusual tint is caused by weather conditions. Particles released into the atmosphere from a volcano, a monsoon or a forest fire can create a disturbance in the air, which causes the moon to appear blue. This type of blue moon was seen for years after the volcanic eruption of Krakatoa in 1883.

The second and more common explanation of a blue moon is when there are two full moons in one month and the second full moon is called a blue moon. For instance, there were two full moons in July 2004. On July 2, 2004 a full moon occurred in Capricorn and on July 31 at 18:06 GMT a second full moon occurred in Aquarius. If you called the second full moon of July 2004 a blue moon, you were in the majority. But according to a recent article posted on Sky &Telescope's website, the majority is wrong.

In the same posting S&T took responsibility for perpetuating the case of mistaken identity. After diligent research, S&T traced the source of its error to an article published in a 1946 edition of the magazine. This article, which defined the second full moon of the month as a blue moon, was based on a misinterpretation of data taken from the 1937 edition of the Maine Farmer's Almanac.

The error appears to have spread from print to the airwaves during a 1980 public radio broadcast of Star Date. On this popular astronomy program the second full moon of the month was called a blue moon by citing the earlier Sky & Telescope article. A quick check of July 31 in Maynard's Pocket Astrologer 2004 will confirm that this modern folklore is still in common use today.

According to S&T, there is an earlier the earlier definition of a blue moon that comes from the original1930-40's editions of the Maine Farmer's Almanac, which is known for providing a wealth of astrological information about the moon. The MFA reference to a blue moon is much more complex than the second of two full moons in one month. The MFA defines a blue moon as the third full moon in any season that contains four full moons instead of the usual three. This third blue moon occurs in the month that precedes the solstice or equinox. Since the four seasons are marked by the ingress of the sun into the cardinal signs, the blue moon months preceding these points are February, May, August and November. Using this MFA definition of a blue moon we conclude that the second full moon of July 2004 cannot be considered a true blue moon for two reasons. The first is that there were not four full moons between the summer solstice and the fall equinox and the second is that the July 31 full moon did not occur in the month preceding the equinox.

This type of blue moon that is not related to either the weather or calendar but is based on the positions of the stars is a bit harder to calculate which is perhaps one of the reasons it is not widely known or used. The next time a true blue moon will occur is on August 19, 2005. This full moon in Aquarius is the third full moon of four that occur between the summer solstice on June 22 and the fall equinox on September 22.

The use in modern folklore of a blue moon as a second full moon in the same month will probably remain popular in the minds of the general public. But the more obscure blue moon defined by the Maine Farmer's Almanac is based on astrophysical data which may make the significance of a blue moon of greater interest to astrologers.

Bibliography
~ http://www.skyandtelescope.com, "What's a Blue Moon?"
~ http://science.nasa.gov "Blue Moon"
~ Hiscock. Philip. Folklore of the "Blue Moon"
~ The American Ephemeris for the 21st Century

Pam Ciampi, C.A.P. is the President of the San Diego Astrological Society, and a longtime member of the Boston NCGR who has practiced astrology since 1975. Her third gardening almanac, Gardening by the Light of the Moon 2005 will be published in September. Pam can be reached at www.pciampi-astrology.com. or pam@pciampi-astrology.com.

© 2004 by Pam Ciampi

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