Normally, there is one full moon per month. But in 2020, October will have two full moons — one on Thursday, October 1 and then again on Halloween.
According to NASA, the rare phenomenon is called a blue moon.
Despite the name, the blue moon will not actually appear blue in color. In fact, a blue moon does not look any different than a regular, monthly full moon.
NASA says a blue moon usually only occurs every two-and-a-half years. The last blue moon appeared on March 31, 2018.
The term blue moon has been used to describe the second full moon in a calendar month since the 1940s. It inspired the phrase “once in a blue moon…”
In recent years people have been using the term “blue moon” to refer to another type of moon, EarthSky reports.
The term can also describe the third of four full moons in a single season — between a solstice and equinox. This is known as a seasonal blue moon.
The next seasonal Blue Moon will occur on Aug. 22, 2021.