Been catching up on a few days of news, and seeing a lot of people refer to the second #FullMoon of August as a blue supermoon. This is not what a #BlueMoon is.
A blue moon is NOT the second full moon in a month. A blue moon is the third full moon in a season that contains four full moons. If, as per the standard definition, northern Summer/southern Winter consists of June, July, and August, then the blue moon was the first full moon last August.
If you go by the traditional Irish definition of the seasons, northern Summer/southern Winter consists of May, June, and July. Under this definition, it is the September full moon that is the blue moon.
In the traditional Chinese definition, which is still used today for cultural festivals in China, Korea, and Vietnam, northern Summer/southern Winter runs from when the sun hits 45° of the ecliptic to when it hits 135°. Under this definition, the blue moon is also the September full moon.
Under the "astronomical" definitions of the seasons, northern Summer/southern Winter runs from the northern solstice to the southward equinox. This is the system used in America, France, and Iran. Under this definition, the second full moon in August was the third in the season, but the next full moon won't be until about a week unto autumn, and so the August full moon is still not a blue moon.
Calendars are an obsession of mine.