Barring pesky clouds, skywatchers will have a spectacular view of a super blue moon when it rises in the evening sky on Monday.
This super blue moon is a rare event.
The “super” part of its title refers to the moon’s orbit, which brings it slightly closer to Earth this month, upping its size and brightness. The “blue” part means that this is the third of four full moons this season, an unusual occurrence.
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. The time between super blue moons can be as much as 20 years – but in general, 10 years is the average.
The next super blue moon will be in January 2037.
When is the super blue moon?
The moon will reach its peak fullness at 2:26 p.m. EDT on Monday. Here in the U.S., it will be below the horizon at that time. However, the moon will look plenty full when it rises in the eastern sky Monday evening. According to NASA, the moon will actually appear full for three days, from Sunday morning through early Wednesday morning.
What causes a supermoon?
The moon’s elongated orbit around the Earth can sometimes cause the moon to appear larger. When the moon is full and its orbit is closest to Earth, the moon is in perigee – the technical name for a super moon.
“Different publications use slightly different thresholds for deciding when a full moon is close enough to the Earth to qualify as a supermoon,” NASA says. “Because the orbit of the moon is not a perfect circle, the moon is sometimes closer to the Earth than at other times during its orbit.”
