lua azul -
Lua Azul. ... Segundo antigo folclore, algumas pessoas dizem que a segunda Lua cheia de um mês é chamada "Blue Moon'' ('' Lua azul''). ...
geocities.yahoo.com.br/rgregio2001/lua_azul.htm

Este próximo sábado, 31 de julio, hay luna llena. Será la segunda en lo que va de mes, después de la que tuvimos el viernes día 2 de julio. El intervalo medio entre dos lunas llenas es de 29,5 días, de tal forma que la presencia de dos en un mismo mes del calendario es un hecho bastante infrecuente. Tanto que esa segunda luna llena del mes hasta tiene nombre propio: se conoce como blue moon, o luna azul.

Español: cada muerte de obispo

English term (edited): once in a blue moon

cada muerte de obispo (Río de la Plata)

Diccionario Oxford

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Note added at 4 hrs 50 mins (2004-08-01 08:58:33 GMT)
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DRAE
de higos a brevas.
1. loc. adv. coloq. Muy de tarde en tarde.
de Pascuas a Ramos.
1. loc. adv. coloq. de tarde en tarde.

Great question! The Hebrew term that comes to my mind to indicate something that happens rarely is translated "once a year". Not very imaginative, considering the whole calendar is a lunar based calendar...ôòí áùðä (Use "Hebrew" in Encoding, if you wish to see the Hebrew letters)

This indicates that something happens quite rarely.

The term is a verbatim translation of the Latin "annus iubilaeus", referring to a section of the Old Testament (3. book of Moses, 25.8 and following), which indicates that the children of Israel every 50 years had to observe a holy year, a so called "hail(ing) year", with forgiving of debts, release of slaves, and return of land sold. Such a year was started by blowing a ram's horn (it's Hebrew name "yôvel" is still contained at the root of "Jubeljahr"). In medival times the term was adopted by the catholic church to refer to a special year of indulgence, initially recurring every 100 years, later then every 50 years, and from 1500 on every 25 years. As various sources point out, the catholic church's opening of a "Jubeljahr" by way of opening and passing through the holy gates is of pagan origin, dating back to ancient Rome. The Roman emperors opened the Janus gate on the Forum Romanum in times of war and closed them in times of peace. Janus in Roman mythology is the god of doors and gates, as well as the god of the beginning, typically depicted with two faces in opposing directions, meant to hint at conflict and contradiction.

[This explanation is based in part on F.A. Brockhaus]


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Note added at 1 day 23 hrs 32 mins (2004-08-03 03:39:56 GMT) Post-grading
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My pleasure; while I appreciated Roberta\'s brief coverage of the German phrase, I felt it deserved a bit more detail.

As far as the _Dogon_ tribe is concerned, please bear in mind that Africa, based on research conducted over the last few decades, in all likelihood has been the cradle of civilization. Ever so often item bearing witness to ancient civilization(s) are found in various parts of Africa, but increasingly in the Sahara desert. As a result, it would be conceivable that the tribe\'s tradition might have been verbally communicated from generation to generation. As far as the catholic church\'s adoption of the 50 year \"celebration\" is concerned, this merely is based on the Hebrew tradition, which in all likelihood has its roots in some modified African ritual. If you go a big further back in history you\'ll for instance encouter Mesopotamia and other high civilizations.