Dark Moon
Dark Moon
(glossary entry)
Description
Several internet authors have advanced the case that the instant in the lunar cycle that astronomers call New Moon -- the moment at which the Moon is in geocentric conjunction with the Sun -- was formerly, and more appropriately, called Dark Moon. The claims that Dark Moon is a traditional astronomical term for this phase appear to be without merit.
Additional Information
- Examples of this phenomenon can be found in the Wikipedia's definitions of Dark Moon and New Moon, in their listings of Lunar Phases, and in internet forums.
- It is implied that the correct traditional term for the Moon at conjunction with the Sun (in the English-speaking world?) is Dark Moon, with the term New Moon having been reserved for the first sighting of the lunar crescent after conjunction. It is certainly true that there has been a long-standing confusion among laymen as to which of these two events the term New Moon applied to, in part because in one case it is being used to denote an instant in the lunar cycle, and in the other to denote the appearance of a young crescent in the sky. See for example, the question on page 632 of The British Apollo (1726). But as the answer explains, the term New Moon has always meant conjunction to (English speaking) astronomers. I have personally been unable to find evidence of any widespread tradition, even among laymen, of calling the Moon at conjunction a Dark Moon, and it certainly never seems to have been a term used by mainstream astronomers. The closest thing to it seems to be use of the term "Luna filens" (Silent Moon?) for the Moon at conjunction in the Jewish ecclesiastic tradition -- see p. 123 of Moses and Aaron (1678). According to the question and answer cited above, the correct astronomical term in use in the 1700's for the first sighting of the lunar crescent after conjunction was not New Moon, but rather "Ortus Heliacus" (Heliacal Rising) -- although this is an expression which seems to have been more widely used to denote the first visible rising of a star, rather than the Moon. - Jim Mosher
- The Oxford English Dictionary (the premier source regarding word histories in the English language) recognizes two main historic uses of the term Dark Moon. One simply means a dark Moon (perhaps obscured by smoke or clouds) as opposed to a bright Moon. The other is taken to be the equivalent of the expression "dark of the Moon" -- which seems to mean a somewhat vaguely defined interval bracketing the astronomer's New Moon in which a lunar crescent cannot be easily seen in the sky; or alternatively when the Moon is not up to provide light during the darkest part of the night. Its historic use, therefore, seems to refer to an interval of several days in the monthly cycle which makes it not quite equivalent to the astronomer's New Moon (meaning the instant of geocentric conjunction).
- The proponents of Dark Moon as a replacement for the astronomer's New Moon imply that when English-speaking astronomers first grappled with the concept of the Moon at conjunction as defining the starting and ending points of sucessive lunar cycles they referred to that instant as the Dark Moon and that only recently have calendar makers replaced that "traditional term" with the more confusing term New Moon. This claim appears to be without foundation.
LPOD Articles
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