Blue Moon Rises Tonight

But what is actually 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 use of the term today is historically incorrect: Originally, a moon was referred to as a "blue moon" if there were four full moons within a season instead of the normal three. The "Blue Moon" was then the third full moon of 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. August and on September 19 the summer has four full moons.

The Maine Farmers Almanac originally defined a blue moon as follows: A blue moon was the third full moon in a season when there had been, exceptionally, four full moons that season. Such "blue moons" could only occur in November, May, February or August. In the Farmers Almanac, each full moon of a year had a specific meaning. For example, there was a “Harvest Moon” in autumn and an “Egg Moon” or “Easter Moon” before Easter. The calendar was also related to the tropical year and ran from one winter solstice to the next. The seasons were also defined somewhat differently than is usual today. Normally there are three full moons in each of these seasons. On rare occasions, however, there was a fourth. And it was precisely in such cases that the third moon of a season was called the "blue moon". The third full moon was chosen because the chronological assignment 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 in time to the solstices or equinoxes of the calendar.

In an article in the March issue of the magazine Sky & Telescope of 1946 about «Blue Moons» contains the crucial 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. This second one in a month, that's how I interpret it, was called the Blue Moon." This misinterpretation by the author quickly caught on. The old definition fell into oblivion 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 actually appears bluish at some point. There are corresponding reports, for example, from the year 1883. The reason for this was the enormous amounts of ash that had been thrown into the atmosphere by the eruption of the Krakatoa volcano. These particles primarily scattered the reddish component of the moonlight, making the moon appear bluish. Tonight, however, such a phenomenon is not to be expected. Incidentally, the funeral service for Neil Armstrong (the first man to walk 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!

The Marcels - Blue Moon