The Supermoon Blue Moon is coming. Here's what to expect

 

Supermoon rises over the Empire State Building in New York City, U.S. on Aug 1, 2023. (Image credit: Fatih Aktas/Anadolu Agency via Getty Images)

The next full moon will occur at 2:26 p.m. EDT (1826 GMT) on Monday, Aug. 19, 2024. But it won't be just any old full moon, it will be a Supermoon Blue Moon! 

Sounds pretty cool, but what exactly does that mean? Let's take a look at what makes a "supermoon" and a "Blue Moon" (and what makes a two-in-one Supermoon Blue Moon, of course).

The term "supermoon" was first coined by astrologer Richard Nolle in 1979, as "either a new or full moon that occurs when the moon is within 90% of its closest approach to Earth" according to NASA. Full supermoons are the biggest and brightest full moons of the year, appearing approximately 30% brighter and 14% larger than usual. Though this may sound like a lot, however, it's quite hard to spot the difference with the unaided eye, unless you're a seasoned moon-watcher. 

Related: Night sky, August 2024: What you can see tonight [maps]

However, in some instances, a supermoon (or even a "regular" full moon, for that matter) can appear huge. Most of the time, though, this has nothing to do with astronomy and everything to do with how the human brain works; this is known as a "moon illusion." The moon illusion is a trick of perception where the moon looks much larger near the horizon than it looks high in the sky.

The two orange circles in the center of the gray circles are the same size, but they look different because of the different sizes of the circles surrounding them. (Image credit: Phrood/Wikimedia Commons)

This illusion occurs because of how our brain interprets distance and size. When the moon is near the horizon, we see it alongside trees, buildings and other objects. That gives us a sense of scale, so our brain compares the moon to these nearby objects, making it appear larger. When the moon is higher up in the sky, there's nothing to compare it to, so it looks smaller. Photographers sometimes use this effect to capture stunning images of distant objects with the moon appearing extremely large behind them. 

The supermoon Blue Moon rises behind the Trabocco of Punta Aderci, near Vasto, Italy, on August 31, 2023. The "moon illusion" at work,  (Image credit: Marco Zac/NurPhoto via Getty Images)

August's supermoon will be the first of four this year, with the others occurring on Sept. 17, Oct. 17 and Nov. 15. The closest supermoon will be October's Hunter's Moon, rising at 7:26 a.m. ET (1126 GMT) on Oct. 17.