The term dark moon describes the last visible

crescent A crescent shape (, ) is a symbol or emblem used to represent the lunar phase in the first quarter (the "sickle moon"), or by extension a symbol representing the Moon itself. In Hinduism, Lord Shiva is often shown wearing a crescent moon on hi ...

of a waning

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

. The duration of a dark moon varies between 1.5 and 3.5 days, depending on its

ecliptic latitude The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System bodi ...

. In current

astronomical Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galax ...

usage, the

new moon In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclipse. ...

occurs in the middle of this dark period, when the Moon and

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

are in

conjunction Conjunction may refer to: * Conjunction (grammar), a part of speech * Logical conjunction, a mathematical operator ** Conjunction introduction, a rule of inference of propositional logic * Conjunction (astronomy), in which two astronomical bodies ...

. 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'' defines the

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 The Moon orbits Earth in the prograde direction and completes one revolution relative to the Vernal Equinox and the stars in about 27.32 days (a tropical month and sidereal month) and one revolution relative to the Sun in about 29.53 days (a ...

is divided into 30 segments, as the

ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...

did in the time of Homer, the Babylonians did, and the Indians still do today (calling them ''

tithi In Vedic timekeeping, a ''tithi'' is a uration of two faces of moon that is observed from earth known as ''milа̄lyа̄'' (𑐩𑐶𑐮𑐵𑐮𑑂𑐫𑐵𑑅, मिलाल्याः) in Nepal Bhasa, or the time it takes for the longi ...

''), the last phase is called the "dark moon". In Greek, it was called the "old moon" and associated with

Hecate Hecate or Hekate, , ; grc-dor, Ἑκάτᾱ, Hekátā, ; la, Hecatē or . is a goddess in ancient Greek religion and mythology, most often shown holding a pair of torches, a key, snakes, or accompanied by dogs, and in later periods depicte ...

. In India, it is called

Amavasya Amāvásyā () is the lunar phase of the new moon in Sanskrit. Indian calendars use 30 lunar phases, called tithi in India. The dark moon tithi is when the Moon is within 12 degrees of the angular distance between the Sun and Moon before conjun ...

and associated with

Kali Kali (; sa, काली, ), also referred to as Mahakali, Bhadrakali, and Kalika ( sa, कालिका), is a Hindu goddess who is considered to be the goddess of ultimate power, time, destruction and change in Shaktism. In this tradi ...

.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 \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in p ...

between the Moon and the Sun before

(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 only directly on the solar year. The most commonly used calendar, the Gre ...

, and not 1.5 to 3.5 days as stated earlier.

References

Phases of the Moon New moon {{Moon-stub

Dark moon as the 30th division

See also

References