Rare Friday the Thirteenth Full Moon
By Geoff Gaherty, Starry Night Education
June 13, 2014; 9:30 AM
Over the next few nights, the full moon will be riding low in our summer sky.
The summer solstice will occur Saturday (June 21), so the noontime sun is nearly at the highest it can get in our Northern Hemisphere skies. This puts the full moon, occurring just after midnight Eastern Daylight Time on Friday the 13th, at close to the lowest it can possibly get this week.
The full moon is an instantaneous event: the exact instant when sun, Earth and moon fall closest to a straight line. A moment before this, the moon is in waxing gibbous phase; a moment after, it is in waning gibbous phase. Only at exactly 12:11 a.m. EDT (0411 GMT) is it exactly "full." [The Moon: 10 Surprising Facts]
As far as the naked eye is concerned, the moon looks full for a day or two on either side of the exact "full" phase. Only with a telescope can you see that the moon is being lit from a slight angle, causing the line of sunrise or sunset on the moon, called the terminator, to be very close to one edge or the other.
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