The blue moon is the second of two full moons in a single month. Each month usually hosts only one full moon, but blue moons sometimes arise because the lunar cycle is 29.5 days long — just short of the length of an average calendar month. This difference means that some months see two full moons.
That is exactly what will happen in August: The first full moon popped up on Aug. 1, and the second will come the evening of Aug. 30.
What is a blue supermoon?
A supermoon occurs when the full moon phase of the lunar cycle syncs up with the perigee, or when it is nearest to the Earth. Supermoons appear brighter and bigger than regular full moons. According to NASA, the apparent size increase is 14 percent, which is about the difference between a nickel and a quarter.
Supermoons are generally seen every three or four months. This one will be the third this year and the second this August. Blue moons, on the other hand, only happen every two or three years (hence the phrase “once in a blue moon”). Blue supermoons are even rarer, occurring once every 10 years or so. The last one was in 2018 during a lunar eclipse, and the next blue supermoons will occur as a pair in 2037.
Will the moon actually look blue?
No. The term “blue moon” doesn’t really describe its color, and the moon will mostly appear to be its usual milky gray. (Certain phenomena, like wildfires and volcanic eruptions, can tint the moon blue, the same visual effect that gave North American skies an orange hue this summer.)
According to NASA, the term “blue moon” used to refer to the third full moon in a season that had four full moons. The newer definition — the second full moon in a month — was coined by the magazine Sky & Telescope in 1946.
How can I see it?
Unlike some other celestial events, everyone on Earth sees the same phases of the lunar cycle at night, so the blue supermoon will be visible everywhere. That means all you have to do is look up at the night sky to see it. NASA recommends using binoculars or a telescope to see more of the moon’s texture.
In the United States, the moon will appear full on Tuesday, Wednesday and Thursday night. On Wednesday evening, you might also spot a bright dot to the upper right of the moon. That’s Saturn, a few days shy of reaching its closest point to Earth. The ringed planet will swing clockwise around the moon during the night.