Immortalized by Elvis Presley and having spawned a phrase used to describe something rare, blue moons are part of pop culture - despite not actually being blue or all that rare.

Essentially, the term blue moon describes the times when there are more full moons than usual.

A blue moon is the third full moon in a season or the second full moon in a month, according to EathSky.org. Something that only happens every two to three years on average.

The last blue moon occurred on Dec. 31, 2009. The next blue moon will happen on July 31, 2015, according to msnbc.com.

Alpharetta residents could see the full moon at its largest Friday, Aug. 31 at 9:58 a.m., if we see it at all since the National Weather Service predicts cloudy weather that may eclipse our view.