Black moon

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Template:Use dmy dates Template:Short description {{#invoke:other uses|otheruses}} No single, universally accepted definition for the term black moon exists.<ref name="timeanddate" /> It is not a term used in astronomy.

The first known use of term is in 2016.<ref name="timeanddate" />Template:Efn Among the meanings ascribed to it are these: a second new moon that appears in the same month; the third new moon in an astronomical season with four new moons; the absence of a new moon in February; or the absence of a full moon in February.<ref name="timeanddate" />

Definitions, frequency, dates

Month with two new moons

One use of the term is for the occurrence of a second new moon in a calendar month. This is analogous to the by-month definition of a blue moon as the second full moon in a month. February is too short for a second new moon to occur. This event occurs about 7 times every 19 years. <ref name="timeanddate">Template:Cite web</ref><ref name="Harper">Template:Cite web</ref><ref name="Odenwald">Template:Cite web</ref><ref name="Cain">Template:Cite news</ref><ref name="Rao">Template:Cite news</ref><ref name="Morrison">Template:Cite book</ref>

The assignment of a calendar date to a new moon, and in which month a second new moon occurs, depends on the time zone. For example, the new moon of 2016-10-01T00:11 UTC occurs on 1 October for Europe, Asia and Oceania, making it the first of two new moons in October. However, for the Americas the date is still 30 September, making this the second new moon of September.<ref name="timeanddate" /><ref name="Rao" />

Calculated in UTC, instances of a second new moon in a calendar month between 2010 and 2020 are:<ref name="usno">Template:Cite web</ref><ref name="usno pdf">Template:Cite web</ref>

  • 2011-07-30
  • 2014-01-30
  • 2014-03-30
  • 2016-10-30
  • 2019-08-30

Season with four new moons

Another use of the term is for the third new moon in a season that has four new moons. This is analogous to the Farmers' Almanac definition of a blue moon as the third full moon in a season with four full moons. A season lasts about three months and usually has three new moons. This event occurs about every 33 months.<ref name="timeanddate" /><ref name="Harper" />

There is no dependency on time zones in this definition as the seasons are tied to the winter solstice. Instances of four new moons in a season are:<ref name="Harper" /><ref name="usno" /><ref name="usno pdf" />

  • 2012-05-20
  • 2015-02-18
  • 2017-08-21
  • 2020-05-22 or 2020-08-19. This depends on the exact definition of the seasons: If northern summer is deemed to begin at the June solstice then the 2020-06-21 new moon occurs in northern summer. If the seasons are defined in quarter tropical years from the December solstice then the 2020-06-21 new moon occurs in northern spring.

Month without full moon

Another use of the term is for the absence of the full moon from a calendar month. This can occur only in February; it happens about every 19 years. When February is without full moon, then the preceding December or January and the following March or April will have two full moons each.<ref name="timeanddate" />

As with the case of two new moons in a month, whether a black moon by this definition occurs depends on the time zone. Calculated in UTC, instances of a month without full moon between 1990 and 2040 are:<ref name="usno" /><ref name="usno pdf" />

  • February 1999
  • February 2018
  • February 2037

Month without new moon

Another use of the term is for the absence of the new moon in a calendar month. This can occur only in February; it happens about every 19 years. When February is without new moon, then the preceding December or January and the following March or April will have two new moons.<ref name="timeanddate" />

As with the case of two new moons in a month, whether a black moon by this definition occurs depends on the time zone. Calculated in UTC, instances of a month without new moon between 1990 and 2040 are:<ref name="usno" /><ref name="usno pdf" />

  • February 1995
  • February 2014
  • February 2033

Paganism

In some aspects of paganism, particularly amongst Wiccans, the black moon is considered to be a special time when any rituals, spells, or other workings are considered to be more powerful and effective. Others believe rituals or workings should not be conducted at these times.<ref name="timeanddate" /><ref name="Harper" />

Criticism of terminology

  • The term black moon is not formally established in astronomy and is used at best in the popularization of astronomy.<ref name="timeanddate" />
  • There is no single definition of the term black moon.<ref name="timeanddate" />
  • The new moon itself cannot be observed.<ref name="timeanddate" /><ref name="Harper" /><ref name="Odenwald" /><ref name="Rao" />
  • The lack of a new or full moon in February can only be assigned to the month, not to any particular date; as such, this is also not observable.
  • The event of a black moon is an artefact of how the Gregorian calendar or the seasons map onto lunations. There is no physical or geometric difference between a black moon and other instances of a new moon.

Notes

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See also

References

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Template:The Moon

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