Lookups spiked on March 19, 2011.
The full moon of March 19th coincided with the point in the moon's orbit that is nearest the Earth, causing the moon to appear unusually large.
This "perigee moon" occurs because the moon's orbit is oval in shape, bringing the moon closer to the Earth on one side than on the other. A full moon on the opposite end of the elliptical orbit - the "apogee" side - would be 50,000 km farther from the Earth and appear 14% smaller than a full moon on the perigee side.
Perigee comes from the Greek words peri ("around" or "near") and geo ("earth").
Photo credit: Jeff Denberg