Blue moon
A Blue Moon (English " Blue Moon " ) is commonly known in the English-speaking world the name for a second full moon in a month. In older astronomical definition thus is referred to in a season with four full moons, the third full moon. In everyday language, we think therefore something very rare with the saying once in a blue moon.
The origin
The term originally referred to Blue Moon in the English language only sporadically occurring, very rare event. It was fixed the first time, writing in 1528 in the small piece of speech Me and Be Not Wroth:
" Yf they say the mone is blewe We must believe did it is true. "
The Blue Moon in the 19th century
Over several intermediate stages, he was taken in the early 19th century in the United States with astronomical events connected, probably by the moon due to volcanic eruptions, etc. really shines sometimes bluish. Also, have played a special role in agriculture at that time the moon phases. The full moons were numbered respectively the first, second and last full moon of the season. Due to the difference between synodischem month ( about 29.5 days) and calendar month, it happens here is that four full moons occur in one season. Then the third full moon of such a season was designated as Blue Moon In Maine Farmers' Almanac in 1819 for the first time.
The Blue Moon in the 20th century
In general ( English ) language knowledge, the definition of Blue Moon at the beginning of the 20th century lost. From a misinterpretation of the Maine Farmers' Almanac by the amateur astronomer James Hugh Pruett (1886-1955) with his article "Once in a Blue Moon" in the magazine Sky & Telescope by March 1946 the nowadays more common definition is that a Blue Moon is the second full moon in a calendar month. This happens about 41 times a century and 412 times in the millennium - on average about every 2.4 years and naturally most common in the months with 31 calendar days, while it is possible that in February takes place at all no full moon, such as in the 1999, 2018 and 2037, with such a Blue Moon both in the preceding January and in the following March.
More
Frequencies
- Average constant lengths for day ( Earth's rotation ), month ( lunar month ) and year ( earth's orbit ), corresponding to the values of 2000
- Calendar circuit according to rules of the corresponding calendar
- Synodic period:
- Its probability of Blue Moons shorter for months with a length L and T: 0
- For months with a length L between T and 2 · T: L / T - 1
- For months with a length longer than L 2 · T: 1