If you step outside on a clear night and look up, you might see a big, beautiful full moon. But sometimes, it's not just any full moon; it's a supermoon!

What makes a moon super? We answer this question with help from Universe Today and Slate.

Every 27 days, the Moon completely orbits Earth. When the Moon positions itself opposite the Sun, the half that faces us lights up. We call this a full moon. 

Slate explains that “because the Moon orbits the Earth in an ellipse, not a circle, the distance between us and the Moon changes all the time.” 

When the Moon is closest to Earth in orbit, it reaches perigee. Conversely, when the Moon is farthest from Earth in orbit, it reaches apogee. 

For a supermoon to occur, the Moon must reach its perigee within 24 hours of becoming a full moon. If this happens, the already big and bright full moon appears a little bigger and a little brighter. 

Twenty-two hours and eight minutes before tonight’s moon becomes full, it will reach its perigee at about 222,691 miles from Earth. Because it will reach this distance within 24 hours of becoming full, the moon will be considered a supermoon. 

While each supermoon is special, some are more remarkable than others. For example, on June 23, 2014, the Moon reached perigee just 27 minutes before becoming full, making it an exceptionally super supermoon!