By Kate Bilo

By Kate Bilo

PHILADELPHIA (CBS) — “Once in a blue moon…”

Ever heard that phrase? It makes a blue moon sound like an incredibly rare occurrence, similar to “once in a lifetime”. But in reality, a blue moon is not all that rare, and it’s most certainly not blue! So if you’re outside squinting at the moon trying to discern a blue hue, you can stop now. :)

A blue moon is the second full moon in a month. Most months have one full moon, and most years have 12. Some years, however, you have 13 full moons, and one month that features two full moons. This happens roughly every 2.7 years, so not incredibly rare.

But it’s a good excuse to sit outside on a warm, clear summer night like this one and enjoy the bright and brilliant lunar display above.