A "supermoon" rises this weekend. The biggest and brightest full moon of the year graces the sky early Sunday as our celestial neighbor swings closer to Earth than usual.
Saying something only happens “once in a blue moon” typically means it’s extremely rare. True blue moons — defined as the second full moon in a month — aren’t actually that uncommon, but if you don’t catch the one on Aug. 31, it’ll be three years before you get another chance.