Blue moon? Friday's celestial event comes with a catch

AP News
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Posted: Jul 30, 2015 5:01 PM
Blue moon? Friday's celestial event comes with a catch

WASHINGTON (AP) — This is an astronomy story that comes up only once in a blue moon, like on Friday. Maybe.

When the full moon appears at 6:43 a.m. EDT Friday, it will become the second full moon of July. Geoff Chester of the U.S. Naval Observatory said the traditional definition of a blue moon is two full moons in a month.

It happens about every 2½ years and has nothing to do with color.

But there's a catch that may disqualify this as a blue moon.

Chester said an older definition from a Maine almanac calls a blue moon the fourth full moon in an astronomical season. This is only the second full moon of summer, so by that definition no blue moon.

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The next blue moon will be in January 2018.