Super Full Moon Expected Saturday

The moon may look bigger—and perhaps more beautiful—on Saturday night than it has in nearly 20 years thanks to the expected rare occurrence of a near-perfect "super full moon."

A full moon arises when the moon, which orbits the Earth on an elliptical course, is on the opposite side of the Earth from the sun, bringing all three into alignment. A "super full moon" or super moon, occurs when it's time for a full moon, and the moon is closer to the Earth than it is at any other point in its orbit, an event called perigee.

When a super full moon is near the horizon, it creates an illusion that the moon is unusually large and "so nearby you can almost reach out and touch it," according to NASA. Near-perfect super full moons—when the full moon is within an hour of perigee—only happen every 18 years or so, Geoff Chester of the U.S. Naval Observatory in Washington, D.C. told NASA, adding the last one so big and close was in March 1993. Other, less-perfect super full moons, happen more frequently.

A short NASA video attached to this story helps explain how a super full moon occurs and what to expect, including what might happen to the tides.

More resources:

• NASA: Super Full Moon (with diagrams)
• National Oceanic and Atmospheric Administration: 'Super Full Moon' Not Expected to Produce High Tides (includes explanation of perigee and other terms)