Blue moon last night?

WASHINGTON – This is an astronomy story that comes up only once in a blue moon, like last night. Maybe.

When the full moon appeared last night, it became 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 two and a half 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 it’s no blue moon.

The next blue moon will be in January 2018.