A waning moon
The term dark moon describes the last visible
crescent
A crescent shape (, ) is a symbol or emblem used to represent the lunar phase (as it appears in the northern hemisphere) in the first quarter (the "sickle moon"), or by extension a symbol representing the Moon itself.
In Hindu iconography, Hind ...
of a waning
Moon
The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
. The duration of a dark moon varies between 1.5 and 3.5 days, depending on its
ecliptic latitude. In current
astronomical
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include ...
usage, the
new moon occurs in the middle of this dark period, when the Moon and
Sun are in
conjunction. This definition has entered popular usage, so that calendars will typically indicate the date of the "new moon" rather than the "dark moon".
Dark moon as the 30th division
The ''
Oxford English Dictionary
The ''Oxford English Dictionary'' (''OED'') is the principal historical dictionary of the English language, published by Oxford University Press (OUP), a University of Oxford publishing house. The dictionary, which published its first editio ...
'' defines the
new 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 the
Moon's orbit is divided into
30 segments, as the
ancient Greeks did in the time of Homer, the
Babylonia
Babylonia (; , ) was an Ancient history, ancient Akkadian language, Akkadian-speaking state and cultural area based in the city of Babylon in central-southern Mesopotamia (present-day Iraq and parts of Kuwait, Syria and Iran). It emerged as a ...
ns did, and the Indians still do today (calling them ''
tithi''), the last phase is called the "dark moon". In Greek, it was called the "old moon" and associated with
Hecate. In India, it is called
Amavasya and associated with
Kali.
[Cole, Freedom. Amāvāsya and Pratipad. ''Jyotish Digest'', Vol XI, Issue II, April–Sep 2014] 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° of
angular distance
Angular distance or angular separation is the measure of the angle between the orientation (geometry), orientation of two straight lines, ray (geometry), rays, or vector (geometry), vectors in three-dimensional space, or the central angle subtende ...
between the Moon and the Sun before
conjunction (a type of
syzygy). The new moon occurs within the 12° after syzygy. This 12°
arc is called ''uma'' by the Babylonians and ''tithi'' 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 orbital
anomaly. This means that the "dark moon" actually lasts approximately 23 hours and 37 minutes and includes any time marked as "new moon" on a
lunar calendar
A lunar calendar is a calendar based on the monthly cycles of the Moon's phases ( synodic months, lunations), in contrast to solar calendars, whose annual cycles are based on the solar year, and lunisolar calendars, whose lunar months are br ...
, and not 1.5 to 3.5 days as stated earlier.
See also
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References
{{DEFAULTSORT:Dark Moon
category:new moon
category:phases of the Moon