Supermoon June 2013
Photo Credit: Divya M. Persaud, University of Rochester
The Moon makes an elliptical orbit around the Earth. This means that rather than having a single radius like a circle, the orbit has a semi-major axis, or long axis, and semi-minor axis, or short axis. Bodies with elliptical orbits thus reach points of maximum and minimum distances from the bodies they orbit (based purely on the elliptical shape).
The Moon reaches its closest approach with the Earth at what is called its perigree. When the perigree coincides with a full phase, the result is what is called outside of astronomy a “supermoon,” a term that actually comes from astrology. During this time, the Moon appears 14% closer and 30% brighter than when it is at apogee, or its farthest distance from Earth.
The next “supermoon” will occur in August 2014.