Worm Supermoon to Illuminate the Sky This Week On March 9, the Full Worm Moon, the first supermoon of 2020, will be visible in the night sky. A supermoon occurs when the moon is on its closest orbital approach to Earth, or within 90 percent of perigee. According to NASA, although the true full moon will only be on Monday, the moon will continue to appear full until early Wednesday. The name, Full Worm Moon, is derived from the way in which Native Americans would use the moon to track the seasons. In this case, the March full moon was associated with the softening of the ground, which caused earthworms to begin to appear. The Full Worm Moon is also referred to as the sugar moon, because of the arrival of spring and the Lenten moon, as it occurs during the Catholic season of Lent. 2020 is expected to have up to four supermoons total, with the next supermoon set to appear on April 7.