The moon will officially become full on Aug. 26 at 7:56 a.m. EDT (1156 GMT). For New York City observers, that's after moonset, but the moon won't be noticeably smaller when it rises again at 8:01 p.m., some 24 minutes after the sun sets.

Before the nearly full moon sets on that morning, Mercury will be near its greatest western elongation (or greatest angular distance) from the sun at about 3:59 p.m. EDT (1959 GMT), according to NASA. The planet will be 18.3 degrees from the sun along the line of the ecliptic, which is a projection of the plane of Earth's orbit against the sky. (Your clenched fist held at arm's length measures about 10 degrees.) [The Brightest Planets in August's Night Sky: How to See Them (and When)]