May’s second full moon will be a blue moon (opens in new tab)

A full moon on May 31 will be a blue moon under the common calendar definition, because it will be the second full moon in May after one on May 1. The term does not mean the moon will appear blue; it reflects the mismatch between a roughly 29.5-day lunar cycle and a calendar year based on the apparent yearly return of the stars to the same positions in the sky. Space.com said the blue-white point near the waxing moon on May 26 is Spica, whose light comes from two large stars orbiting each oth...