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The termdark moon describes the last visiblecrescent of a waningMoon. The duration of a dark moon varies between 1.5 and 3.5 days, depending on itsecliptic latitude. In currentastronomical usage, thenew moon occurs in the middle of this dark period,[1] when the Moon andSun are inconjunction. This definition has entered popular usage, so that calendars will typically indicate the date of the "new moon" rather than the "dark moon".
TheOxford English Dictionary defines thenew moon as "the first visible crescent of the Moon, after conjunction with the Sun".Dark moon is a term used for a waning crescent moon. When theMoon's orbit is divided into30 segments, as theancient Greeks did in the time of Homer, theBabylonians did, and the Indians still do today (calling themtithi), the last phase is called the "dark moon". In Greek, it was called the "old moon" and associated withHecate.[2] In India, it is calledAmavasya and associated withKali.[3] Both of these goddesses have a dark connotation, hence the term dark moon.
In Babylonian, Greek, and Indian culture, the dark moon occurs within the 12° ofangular distance between the Moon and the Sun beforeconjunction (a type ofsyzygy). The new moon occurs within the 12° after syzygy. This 12°arc is calleduma by the Babylonians andtithi by the Indians.
The Moon takes a mean duration of 23 hours and 37 minutes to cover this length, but this period can vary from 21 to 26 hours because of the Moon's orbitalanomaly. This means that the "dark moon" actually lasts approximately 23 hours and 37 minutes and includes any time marked as "new moon" on alunar calendar, and not 1.5 to 3.5 days as stated earlier.
