ET>> On Saturday evening, July 31st, a full Moon
 ET>> will rise for the second time this month
 ET>> (the first time was on July 2nd). Many
 ET>> people call the second full Moon in a
 ET>> calendar month a "blue Moon" and use the
 ET>> expression "once in a blue Moon" to mean
 ET>> something that occurs only rarely. While the
 ET>> latter meaning can be traced back centuries,
 ET>> the former definition is much newer -- and
 ET>> it's wrong....

 MM> ....because the local newspaper's tides, sun
 MM> and moon tables give the following times for
 MM> full moon here in Auckland:

Not the reason why.  Blue moons ARE blue.  They have nothing to do with the
number of full moons in a calendar month.  The moon (full or otherwise)
appears blue due to atmospheric scattering.  The longer wavelengths are
scattered by particles (e.g. particles of smoke) leaving the shorter (i.e.
blue) wavelengths.

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