The full moon this weekend will be particularly big and bright, because it's relatively close
Posted by David Brooks | Thursday, May 3, 2012
The full moon on Saturday will be "as much as 14 percent bigger and 30 percent brighter" than the other full moons this year because it will be a perigee (closest to Earth in its elliptical orbit) almost exactly the moment that it lines up with the EArth and Sun to become full (11:34 p.m. on Saturday night, if you're curious).
At perigee the moon is about 225,000 miles away from the Earth; at apogee it's about 250,000 miles away. That's a pretty sizeable difference which can affect tides, although not by much, says NASA:
It's true that a perigee full Moon brings with it extra-high "perigean tides," but according to the National Oceanic and Atmospheric Administration this is nothing to worry about. In most places, lunar gravity at perigee pulls tide waters only a few centimeters (an inch or so) higher than usual. Local geography can amplify the effect to about 15 centimeters (six inches).
This supermoon effect - a full moon very near perigee - happens about once a year.