[Vision2020] Blue moon in July, 2015

[Kenneth Marcy]

Thirty days from date of this message, which has a full moon, will be a 
blue moon -- July 31, 2015, will have the second full moon within the 
calendar month.

https://en.wikipedia.org/wiki/Blue_moon

A *blue moon* is an additional full moon that appears in a subdivision 
of a year, either the third of four full moons in a season or, recently, 
a second full moon in a month of the common calendar.

The term has traditionally referred to an 'extra' moon, where a year 
which normally has 12 moons has 13 instead. The 'blue moon' reference is 
applied to the 3rd moon in a season 
<https://en.wikipedia.org/wiki/Season#Mid-latitude_astronomical> with 4 
moons,^<https://en.wikipedia.org/wiki/Blue_moon#cite_note-SkyTel2-1> 
thus correcting the timing of the last month of a season that would have 
otherwise been expected too early. This happens every two to three years 
(seven times in the Metonic cycle 
<https://en.wikipedia.org/wiki/Metonic_cycle> of 19 
years).^<https://en.wikipedia.org/wiki/Blue_moon#cite_note-BadAstronomy2-2>


Ken

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