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| Celestial Products: Article - Blue Moons | | ||||||||
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There are at two notable definitions for a Blue Moon that are
circulating. The apparent original that has surfaced again recently refers to the third full moon within a season
(astronomical Winter, Spring, Summer, Fall) having four full moons. Normally a season will only have three full moons,
but occasionally, the lunation cycle meshes with the season so that if there is a full moon early in the
season, it is possible to get in four full
moons before the end of that season. The full moon in the last complete month of
days of the season was
dubbed a Blue Moon by a New England farmer’s almanac in the early 1900’s. Thus,
February, May, August,
and November are the only months in which one could have one of these "extra"
seasonal full moons. Using
this definition of a Blue Moon, the full moon of August 19, 2005 is the next
Blue Moon since there are four
full moons in the period between June 21st and September 23rd. Remember, the
Blue Moon is the full moon
of the last full month in that season. Since the seasons have beginning and
ending dates partially into a calendar
month, the Blue Moon will always be the third full moon in the season of four.
Now, let’s look at a more familiar definition of a Blue Moon. A free-lance writer researching the Blue Moon name, mistakenly interpreted the original definition, previously discussed, to be the second full moon that occasionally occurs in a calendar month. His article got by the editors of a magazine without sufficient review and it was published back in the mid-1900’s. This initiated a second Blue Moon definition that has enjoyed an even greater adoption in the public eye - probably due to the growing readership of popular magazines and the greater simplicity of the definition. This definition has permeated much of our western culture and gone unchallenged for decades since few remembered the original farmer’s almanac definition. Since the average lunation takes just over 29.5 days, it is possible to have two full moons within the 30 or 31 day calendar months as long as the first full moon occurs within the first day(s) of the month. One can find one of these Blue Moon months roughly every 2+ years, but this average is hardly a rule that can be used to predict future occurrences. This is due to the varying number of days in each calendar month, leap year, and the variance from the 29.5 day average lunation period. Under this Blue Moon definition, a Blue Moon occurs July 31, 2004 since there will be a full moon earlier in the month on July 2. The name Blue Moon may otherwise apply to the rare occurrence of seeing a blue colored Moon as a result the moonlight being filtered through atmospheric particles that scatter more of the yellow-red wavelengths than the green-blue wavelengths. This has a good possibility during the ash eruptions that Mount St. Helens in Washington state U.S.A. has been providing during the latter part of September and into October 2004. Western North America has the best possibility of seeing this type of Blue Moon. Of course, light from the sun filtered through the same particles can produce a blue sun effect as well. Hunting for Blue Moons? Our charts 20th and 21st Century Luna provide all the daily phases for each century. Contact Celestial Products for a local supplier or request our catalog of science/astronomy publications. Copyright 2003, 2004 by Larry Bohlayer |