(CNN) — On August 30, a full moon will appear at the closest point to our planet this year — about 222,043 miles (357,344 kilometers) away — making it an elusive super blue moon.
This is thesecond supermoon of the month.
A blue moon, in common parlance, refers to a second full moon that occurs within the same calendar month, which typically happens only once every two and a half years. The most recent blue moon, for example, occurred in October 2020.
But take note: It won’t appear blue, despite the name. The term actually originates from a 16th century expression, in which a blue moon referred to something that never — and later rarely — happened, according to Encyclopaedia Britannica.
What is a full moon, supermoon and blue moon?
A full moon occurs when the near side of the moon is fully illuminated by the sun in the night sky, which typically happens once a month.
Supermoons are more uncommon.
These lunar displays occur because the moon does not travel in a perfect circle around Earth. Rather, the moon’s path is shaped like an oval, bringing the moon closer to the Earth at certain points on its elliptical journey. The exact distance between Earth and the moon can vary by about 26,222 miles (42,200 kilometers), according to NASA.
Supermoons occur when the moon is near or at its closest point to Earth (or, in scientific terms, its perigee) while also appearing full.
Scientists call this a “perigean full moon,” and it can be up to 30% brighter and appear about 14% larger than full moons that occur at the farthest point from Earth, according to the United Kingdom’s National Space Centre.
Some argue that the term supermoon is overused because it can refer to full moons that don’t occur at the absolute nearest point to Earth — and they don’t always appear drastically different to the human eye than the average full moon.
As NASA explains, while supermoon isn’t an official astronomical term, “it’s used to describe a full Moon that comes within at least 90 percent of perigee.” And these lunar events aren’t uncommon: Supermoons typically occur three or four times per year.
In fact, the instances where the moon looks largest in the sky are typically when it appears close to the horizon, creating an optical illusion, notes researcher Adam Block, an operations specialist at the University of Arizona’s Steward Observatory in Tucson. And that phenomenon has nothing to do with whether the moon is in supermoon territory.
“If you turn around in the opposite direction, and if you’re flexible, you can bend over and look between your legs at the moon upside down and the illusion completely disappears,” Block explained.
Supermoons aren’t particularly rare or visually distinctive, but they do impact the Earth. The moon’s physical closeness can cause higher tides in the Earth’s oceans, NASA notes.
Blue moons, however, are rarer. While the term originally referred to an extra full moon occurring within the same tropical year — the period between two equinoxes— it now commonly refers to two full moons appearing within the same calendar month.
Not all blue moons are supermoons, which makes the August 30 full moon even more exceptional. The next time two supermoons will occur in the same month will be January 2037, according to Espenak’s data.
Sometimes, several lunar phenomenon line up on the same night to create a truly extraordinary sky-watching experience, such as on January 31, 2018, when the last full moon of the month was not only a blue moon and a supermoon — it was also a blood moon, or a total lunar eclipse. Those events occur when Earth’s shadow gives the full moon a reddish tint.
