But what exactly is a “blue moon” or “blue moon”? Today the second full moon in a month is usually referred to as the “blue moon”. However, this common usage of the term today is historically incorrect: Originally, a moon was called a “blue moon” if there were four full moons instead of the normal three within a season. The “Blue Moon” was the third full moon this season. There is also such a historically correct “Blue Moon” in August: Since the beginning of summer there have already been full moons on June 23 and July 22. With the full moon on 20./21. On August 19st and September XNUMXth the summer has four full moons.
In the Maine Farmers Almanac, a blue moon was originally defined as follows: A blue moon was the third full moon in a season if, as an exception, there had been four full moons during this season. Such “blue moons” could only exist in November, May, February or August. In the Farmers Almanac, all full moons of a year had a specific meaning. For example, in autumn there was a “harvest moon” and an “egg moon” or “Easter moon” before Easter. The calendar was also based on the tropical year and ran from one winter solstice to the next. The seasons were also defined somewhat differently than usual today. Usually three full moons fell in each of these seasons. In rare cases, however, there was a fourth. And it is precisely in such cases that the third moon of a season was called “blue moon”. The third full moon was selected because the timing of the “normal” full moons with a certain meaning was better preserved and, for example, the last full moon of a season was still relatively close to the solstices or equinoxes of the calendar.
In an article in the March issue of the magazine Sky & Telescope of the year 1946 about “Blue Moons” is the decisive sentence: “Seven times in 19 years there were - and there are - 13 full moons a year. That means eleven months with one full moon each and one month with two. That second in a month, I interpret it, was called the Blue Moon. " This misinterpretation by the author quickly caught on. The old definition was forgotten and today the second full moon of the month is referred to as the “blue moon” everywhere.
Incidentally, it cannot be ruled out that the full moon will actually appear bluish. There are corresponding reports, for example, from the year 1883. The reason for this were enormous amounts of ash that had been hurled into the atmosphere by the eruption of the Krakatau volcano. These particles mainly scattered the reddish component of the moonlight, so that the moon appeared bluish. Such a phenomenon is not to be expected tonight. Incidentally, the funeral service for Neil Armstrong (the first man on the moon) took place on a day that had a blue moon. The double meaning “to be blue” (to be sad) also plays a symbolic role here. We wolves howl at the moon tonight ... and eat vampires!