There are two definitions of a Blue Moon. The first one describes the third full moon in a season which has four full moons in total. However, the term "Blue Moon" also used to describe a phenomenon that happens every two to three years. This is rarer. It takes a year for the Earth to orbit the Sun once and the Moon takes 29.5 days to complete one cycle around the Earth. This means that 12 full cycles of the Moon around the Earth takes 354 days. That's less than the 365 days (or 366 days during a leap year) in our calendar year. As the time frames don't quite match up, every two to three years we end up getting a 13th full moon, with two full months seen in a single month.

August 2024's Blue Moon fits the rarer definition of Blue Moon. It is the third full moon in a season that has four full moons, which is less common than the typical three. Tonight's full moon will also make 2024 a 13 Full Moon year. The next Blue Moon like this one isn't expected until 2026.

Tonight's full moon is also a Super Moon. A Supermoon is when a full Moon is closest to the Earth, appearing bigger and brighter than normal - up to 15% brighter and 30% bigger than regular full Moons.