WASHINGTON: 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 (1043 GMT) in the US Friday, it will become the second full moon of July. Geoff Chester of the US 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 colour.
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.
The next blue moon will be in January 2018.