So, what do these terms mean? The "super" part refers to the moon's orbit, which brings it slightly closer to Earth this month, making it appear bigger and brighter. When a supermoon occurs, a full moon is at its closest point to the Earth, resulting in a stunning and awe-inspiring sight. The moon appears significantly larger and radiates a brilliance that is up to 15% brighter than a typical full moon. The "blue" part means this is the third of four full moons this season, an unusual occurrence. How rare is the super/blue combination? A blue moon happens once every two or three years on average, according to NASA, but a blue moon that's also a supermoon is even more uncommon. Super blue moons can come as much as 20 years apart – but generally, 10 years is the average.