August 1, 2015 9:58 AM EDT
T he second full moon of July rose Friday night, a phenomenon referred to as a “blue moon.”
Though the phrase “once in a blue moon” is meant to describe a rare event, a blue moon is neither rare, or blue. “Blue moon” is actually a term used to describe the second full moon in a single calendar month. Most years only have 12 moons, but this year has 13, which happens every two to three years, according to astronomers. “Blue moons” don’t actually appear blue, but the moon can appear blue after events on earth like wildfires and volcanic eruptions, according to NASA .
PHOTOS: 20 Breathtaking Images of Earth From Space Aleppo, Syria, May 26, 2013 – The Citadel of Aleppo – medieval fortified palace DigitalGlobe—Getty Images Belfast, Northern Ireland, Nov. 3, 2013 – “Wish,” a large-scale art work DigitalGlobe—Getty Images Utah, USA, April 22, 2013 – Colorado River DigitalGlobe—Getty Images Cuanza River, Angola, April 28, 2013 – Cambambe Dam DigitalGlobe—Getty Images Doha, Qatar, March 4, 2013 – Artificial island spanning nearly four million sq meters. DigitalGlobe—Getty Images Dunalley, Australia, Jan. 6, 2013 – fires, false color image (red = healthy vegetation) DigitalGlobe—Getty Images Australia, April 22, 2013 – Great Barrier Reef DigitalGlobe—Getty Images Gwadar coast, Pakistan Sept. 29, 2013 – new island created by earthquake in Pakistan DigitalGlobe—Getty Images Croatia, Feb. 16, 2013 – Galešnjak (Island of Love) DigitalGlobe—Getty Images Hong Kong, China May 9, 2013 – giant rubber duck DigitalGlobe—Getty Images Madang Province, Papua New Guinea, March 22, 2013 – Manam Volcano DigitalGlobe—Getty Images Namib Desert, Namibia, May 13, 2013 – Sossusvlie area DigitalGlobe—Getty Images Naples, Italy, Feb. 19 2013 – Mount Vesuvius DigitalGlobe—Getty Images Niger, Feb. 13, 2013 – Arlit Uranium Mine DigitalGlobe—Getty Images Schooner Cays, Bahamas, May 26, 2013 DigitalGlobe—Getty Images Sochi, Russia, March 17, 2013 – Site of 2014 winter Olympics DigitalGlobe—Getty Images Near the city of Sur, Oman, Feb. 13, 2013 – massive “green tide” DigitalGlobe—Getty Images Valencia, Spain, July 19, 2013 – Palau de les Arts Reina Sofia and Gulliver Park with an enormous fiberglass model of Lemuel Gulliver trapped DigitalGlobe—Getty Images Versailles, France, Aug. 20, 2013 – Palace of Versailles DigitalGlobe—Getty Images Xi'an, China, Sept. 24, 2013 – Shiyuan Park DigitalGlobe—Getty Images More Must-Reads From TIME Why We're Spending So Much Money Now The Fight to Free Evan Gershkovich Meet the 2024 Women of the Year John Kerry's Next Move The Quiet Work Trees Do for the Planet Breaker Sunny Choi Is Heading to Paris Column: The Internet Made Romantic Betrayal Even More Devastating Want Weekly Recs on What to Watch, Read, and More? Sign Up for Worth Your Time