Full moon

"Harvest moon" and "Hunter's moon" redirect here. For other uses, see Harvest moon (disambiguation) and Hunter's moon (disambiguation).

For other uses, see Full moon (disambiguation).

The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic longitudes of the Sun and Moon differ by 180°).^[3] This means that the lunar hemisphere facing Earth—the near side—is completely sunlit and appears as an approximately circular disk. The full moon occurs roughly once a month.

The supermoon of 14 November 2016 was 356,511 km (221,526 mi) away^[1] from the center of Earth. This occurs yearly.^[2]

As the Earth revolves around the Sun, approximate axial parallelism of the Moon's orbital plane (tilted five degrees to the Earth's orbital plane) results in the revolution of the lunar nodes relative to the Earth. This causes an eclipse season approximately every six months, in which a lunar eclipse can occur at the full moon phase.

The time interval between a full moon and the next repetition of the same phase, a synodic month, averages about 29.53 days. Therefore, in those lunar calendars in which each month begins on the day of the new moon, the full moon falls on either the 14th or 15th day of the lunar month. Because a calendar month consists of a whole number of days, a month in a lunar calendar may be either 29 or 30 days long.

Characteristics

A full moon is often thought of as an event of a full night's duration, although its phase seen from Earth continuously waxes or wanes, and is full only at the instant when waxing ends and waning begins. For any given location, about half of these maximum full moons may be visible, while the other half occurs during the day, when the full moon is below the horizon. As the Moon's orbit is inclined by 5.145° from the ecliptic, it is not generally perfectly opposite from the Sun during full phase, therefore a full moon is in general not perfectly full except on nights with a lunar eclipse as the Moon crosses the ecliptic at opposition from the Sun.

Many almanacs list full moons not only by date, but also by their exact time, usually in Coordinated Universal Time (UTC). Typical monthly calendars that include lunar phases may be offset by one day when prepared for a different time zone.

The full moon is generally a suboptimal time for astronomical observation of the Moon because shadows vanish. It is a poor time for other observations because the bright sunlight reflected by the Moon, amplified by the opposition surge, then outshines many stars.

Moon Phases

There are eight phases of the moon, which vary from partial to full illumination. The moon phases are also called lunar phases. These stages have different names that come from its shape and size at each phase. For example, the crescent moon, which is banana the quarter moon, is D-shaped. When the moon phases are almost complete, the moon is called the gibbous moon. The crescent and gibbous Moons each last approximately a week.^[4]

Each phase is also described in accordance to its position on the full 29.5 day cycle.

The eight phases of the moon in order include:^[4]

• new Moon
• waxing crescent Moon
• first quarter Moon
• waxing gibbous Moon
• full Moon
• waning gibbous Moon
• last quarter Moon
• waning crescent Moon.

Formula

The date and approximate time of a specific full moon (assuming a circular orbit) can be calculated from the following equation:^[5]

${\displaystyle d=20.362000+29.530588861\times N+102.026\times 10^{-12}\times N^{2}}$ 

where d is the number of days since 1 January 2000 00:00:00 in the Terrestrial Time scale used in astronomical ephemerides; for Universal Time (UT) add the following approximate correction to d:

${\displaystyle -0.000739-(235\times 10^{-12})\times N^{2}}$  days

where N is the number of full moons since the first full moon of 2000. The true time of a full moon may differ from this approximation by up to about 14.5 hours as a result of the non-circularity of the Moon's orbit.^[6] See New moon for an explanation of the formula and its parameters.

The age and apparent size of the full moon vary in a cycle of just under 14 synodic months, which has been referred to as a full moon cycle.

Lunar eclipses

When the Moon moves into Earth's shadow, a lunar eclipse occurs, during which all or part of the Moon's face may appear reddish due to the Rayleigh scattering of blue wavelengths and the refraction of sunlight through Earth's atmosphere.^[7][8][9] Lunar eclipses happen only during a full moon and around points on its orbit where the satellite may pass through the planet's shadow. A lunar eclipse does not occur every month because the Moon's orbit is inclined 5.145° with respect to the ecliptic plane of Earth; thus, the Moon usually passes north or south of Earth's shadow, which is mostly restricted to this plane of reference. Lunar eclipses happen only when the full moon occurs around either node of its orbit (ascending or descending). Therefore, a lunar eclipse occurs about every six months, and often two weeks before or after a solar eclipse, which occurs during a new moon around the opposite node.

In folklore and tradition

See also: List of lunar deities and Lunar effect

 

A full moon rising, seen through the Belt of Venus

In Buddhism, Vesak is celebrated on the full moon day of the Vaisakha month, marking the birth, enlightenment, and the death of the Buddha.^[10]

In Arabic, badr (بدر ) means 'full moon', but it is often translated as 'white moon', referring to The White Days, the three days when the full moon is celebrated.

Full moons are traditionally associated with insomnia (inability to sleep), insanity (hence the terms lunacy and lunatic) and various "magical phenomena" such as lycanthropy. Psychologists, however, have found that there is no strong evidence for effects on human behavior around the time of a full moon.^[11] They find that studies are generally not consistent, with some showing a positive effect and others showing a negative effect. In one instance, the 23 December 2000 issue of the British Medical Journal published two studies on dog bite admission to hospitals in England and Australia. The study of the Bradford Royal Infirmary found that dog bites were twice as common during a full moon, whereas the study conducted by the public hospitals in Australia found that they were less likely.

 

Symbol of the Triple Goddess

The symbol of the Triple Goddess is drawn with the circular image of the full moon in the center flanked by a left facing crescent and right facing crescent, on either side, representing a maiden, mother and crone archetype.^[12]

Full moon names

Historically, month names are names of moons (lunations, not necessarily full moons) in lunisolar calendars. Since the introduction of the solar Julian calendar in the Roman Empire, and later the Gregorian calendar worldwide, people no longer perceive month names as "moon" names. The traditional Old English month names were equated with the names of the Julian calendar from an early time, soon after Christianization, according to the testimony of Bede around AD 700.

Some full moons have developed new names in modern times, such as "blue moon", as well as "harvest moon" and "hunter's moon" for the full moons of autumn.

Lunar eclipses occur only at a full moon and often cause a reddish hue on the near side of the Moon. This full moon has been called a blood moon in popular culture.^[13]

Harvest and hunter's moons

"Harvest moon" and "Hunter's moon" redirect here. For other uses, see Harvest moon (disambiguation) and Hunter's moon (disambiguation).

 

A harvest moon. Its orange color is due to greater Rayleigh scattering as the Moon appears close above the horizon, rather than being unique to harvest moons.^[14]

The "harvest moon" and the "hunter's moon" are traditional names for the full moons in late summer and in the autumn in the Northern Hemisphere, usually in September and October, respectively. People may celebrate these occurrences in festivities such as the Chinese Mid-Autumn Festival, which is as important as the Chinese New Year.

The "harvest moon" (also known as the "barley moon" or "full corn moon") is the full moon nearest to the autumnal equinox (22 or 23 September), occurring anytime within two weeks before or after that date.^[15] The "hunter's moon" is the full moon following it. The names are recorded from the early 18th century.^[16] The Oxford English Dictionary entry for "harvest moon" cites a 1706 reference, and for "hunter's moon" a 1710 edition of The British Apollo, which attributes the term to "the country people" ("The Country People call this the Hunters-Moon.") The names became traditional in American folklore, where they are now often popularly attributed to Native Americans.^[17] The Feast of the Hunters' Moon is a yearly festival in West Lafayette, Indiana, held in late September or early October each year since 1968.^[18] In 2010 the harvest moon occurred on the night of the equinox itself (some 51⁄2 hours after the moment of equinox) for the first time since 1991, after a period known as the Metonic cycle.^[19][20]

All full moons rise around the time of sunset. Since the Moon moves eastward among the stars faster than the Sun, lunar culmination is delayed by about 50.47 minutes^[21] (on average) each day, thus causing moonrise to occur later each day.

Due to the high lunar standstill, the harvest and hunter's moons of 2007 were special because the time difference between moonrises on successive evenings was much shorter than average. The moon rose about 30 minutes later from one night to the next, as seen from about 40° N or S latitude (because the full moon of September 2007 rose in the northeast rather than in the east). Hence, no long period of darkness occurred between sunset and moonrise for several days after the full moon,^[22] thus lengthening the time in the evening when there is enough twilight and moonlight to work to get the harvest in.

Farmers' Almanacs

"Snow Moon" redirects here. For the song by Adonxs, see Age of Adonxs.

The Maine Farmers' Almanac from around the 1930s began to publish Native American "Indian" full moon names, some of which had been adopted by colonial Americans.^[23] The Farmers' Almanac (since 1955 published in Maine, but not the same publication as the Maine Farmers' Almanac) continues to do so.^[24]

An early list of "Indian month names" was published in 1918 by Daniel Carter Beard in his The American Boy's Book of Signs, Signals and Symbols for use by the boy scouts.

Such names have gained currency in American folklore. They appear in print more widely outside of the almanac tradition from the 1990s in popular publications about the Moon. Mysteries of the Moon by Patricia Haddock ("Great Mysteries Series", Greenhaven Press, 1992) gave an extensive list of such names along with the individual tribal groups they were supposedly associated with.^[25] Haddock supposes that certain "Colonial American" moon names were adopted from Algonquian languages (which were formerly spoken in the territory of New England), while others are based in European tradition (e.g. the Colonial American names for the May moon, "Milk Moon", "Mother's Moon", "Hare Moon" have no parallels in the supposed native names, while the name of November, "Beaver Moon" is supposedly based in an Algonquian language).

The Long Night's Moon is the last full moon of the year and the one nearest the winter solstice.^[26]

"Ice Moon" is also used to refer to the first full moon of January or February.^[27]

Full moon names the Farmer's Almanac

Month	Names according to Beard^[28]		Names from the Farmers Almanac^[29]^[clarification needed]	Other names
January	Difficulty	Black Smoke	Wolf Moon^[30]	Old Moon	Moon After Yule	Winter Moon	—
February	Raccoon	Bare Spots on the Ground	Snow Moon	Hunger Moon	Storm Moon	—	—
March	Wind	Little Grass, Sore-Eye	Worm Moon	Crow Moon	Sap Moon	Crust Moon	Lenten Moon, Wind Moon
April	Ducks	Goose-Eggs	Pink Moon	Seed Moon, Sprouting Grass Moon	Fish Moon, Frog Moon	Spring Moon, Awakening Moon	Sap Moon
May	Green Grass	Root-Food	Flower Moon	Milk Moon	Corn Planting Moon	Grass Moon	Mother's Moon
June	Corn-Planting	Strawberry	Strawberry Moon	Mead Moon	Rose Moon	Hot Moon	Thunder Moon
July	Buffalo (Bull)	Hot Sun	Buck Moon	Hay Moon	Elk Moon	Summer Moon	Thunder Moon
August	Harvest	Cow Buffalo	Sturgeon Moon	Red Moon	Corn Moon	Barley, Green Corn, Herb, or Grain Moon	Dog Moon
September	Wild Rice	Red Plum	Harvest Moon	Full Corn Moon	Fruit Moon	Barley Moon	—
October	Leaf-Falling	Nuts	Hunters' Moon	Blood or Sanguine Moon	Autumn Moon	Pumpkin Moon	Dying Moon
November	Deer-Mating	Fur-Pelts	Beaver Moon	—	Frosty Moon	Dark Moon	—
December	Wolves	Big Moon	Cold Moon	Oak Moon	Long Night's Moon	—	—
13th	—	—	—	Blue Moon^[31]	—	—	—

Hindu full moon festivals

See also: Purnima

In Hinduism, most festivals are celebrated on auspicious days. Many Hindu festivals are celebrated on days with a full moon night, called the purnima. Different parts of India celebrate the same festival with different names, as listed below:

1. Chaitra Purnima – Gudi Padua, Ugadi, Hanuman Jayanti (15 April 2014)^[32]
2. Vaishakha Purnima – Narasimha Jayanti, Buddha Jayanti (14 May 2014)^[33]
3. Jyeshtha Purnima – Savitri Vrata, Vat Purnima (8 June 2014)^[34]
4. Ashadha Purnima – Guru Purnima, Vyasa Purnima
5. Shravana Purnima – Upanayana ceremony, Avani Avittam, Raksha Bandhan, Onam
6. Bhadrapada Purnima – Start of Pitru Paksha, Madhu Purnima
7. Ashvin Purnima – Sharad Purnima
8. Kartika Purnima – Karthikai Deepam, Thrukkarthika
9. Margashirsha Purnima – Thiruvathira, Dattatreya Jayanti
10. Pushya Purnima – Thaipusam, Shakambhari Purnima
11. Magha Purnima
12. Phalguna Purnima – Holi

Lunar and lunisolar calendars

 

The December 2015 full moon coincided with Christmas.^[35] This last occurred in 1977 (for the American timezones). A small horizontal libration is visible comparing their appearances. By the 19-year metonic cycle the full moon will repeat on Christmas Day in 2034, 2053, 2072, and 2091.^[36]

Main article: Lunar calendar

Most pre-modern calendars the world over were lunisolar, combining the solar year with the lunation by means of intercalary months.^[37][38] The Julian calendar abandoned this method in favour of a purely solar reckoning while conversely the 7th-century Islamic calendar opted for a purely lunar one.

A continuing lunisolar calendar is the Hebrew calendar. Evidence of this is noted in the dates of Passover and Easter in Judaism and Christianity, respectively. Passover falls on the full moon on 15 Nisan of the Hebrew calendar. The date of the Jewish Rosh Hashana and Sukkot festivals along with all other Jewish holidays are dependent on the dates of the new moons.^[39]

Intercalary months

Main article: Intercalary month

In lunisolar calendars, an intercalary month occurs seven times in the 19 years of the Metonic cycle, or on average every 2.7 years (19/7). In the Hebrew calendar this is noted with a periodic extra month of Adar in the early spring.

Blue moon

Further information: Blue moon

In the modern system of "traditional" American full moon names tied to the solstice and equinox points, a supernumerary full moon in such a period is called a blue moon. The term "blue moon" used in this sense may date to as early as the 16th century, but it became well known in the United States due to the Farmers' Almanac (published since 1818).^[a]

According to the pattern of use in the Farmers' Almanac, a "blue moon" is the third full moon in any period between either a solstice and an equinox, or between an equinox and a solstice, (calculated using the mean tropical year), which contains four full moons.^[41] These seasons are equal in length, unlike the astronomical ones, which vary in length depending on the Earth's speed in its elliptical orbit round the Sun. To compare, in 1983 the equal-length mean-solar solar points and the actual astronomical (observed) dates are shown in the table below (all dates and times in GMT):

Event	Fictitious equal-length-season date	Actual astronomical date	Error (approximate)
Spring equinox	1:48am, 23 March 1983	4:39am, 21 March 1983	−2 days
Summer solstice	9:15am, 22 June 1983	11:09pm, 21 June 1983	−1.5 days
Fall equinox	4:42pm, 21 September 1983	2:42pm, 23 September 1983	+2 days
Winter solstice	12:10am, 22 December 1983	10:30am, 22 December 1983	−2 hours

As a consequence of checking an inadequate number of old issues of the Farmers' Almanac, the author of an article in the March 1946 issue of Sky & Telescope magazine wrongly concluded that the Farmers' Almanac had used "blue moon" to denote "the second full moon in any month which contains two full moons".

The mistaken rule was retracted and declared "erroneous" in a 1999 Sky & Telescope article, which gave the corrected rule, based on order in seasons.^[42]

Using the original meaning, "blue moons" occur with the same average frequency of intercalary months, 7 times in 19 years; the Farmers' Almanac system of full moon names effectively defines a functioning luni-solar calendar. Because the Sky & Telescope definition depends on calendar months and because February is shorter than a lunar month, there will be a higher frequency of blue moons under that definition (in years in which February squeezes in between two full moons), so that blue moons occur on average about 8 times in 19 years.

It is a rare phenomenon to see an unusual blue color of the moon (not necessarily a full moon) when viewing the Moon. This phenomenon is caused by dust particles or smoke in the atmosphere, and was seen after the forest fires in Sweden and Canada in 1950 and 1951. In 1883, after the eruption of Krakatoa in Indonesia, the Moon was blue for almost two years. Other less violent volcanic explosions have been followed by blue moons. The blue Moon was also seen after the eruption of El Chichon in Mexico in 1983, Mount St. Helens in 1980, and Mount Pinatubo in 1991.^[43]

See also

•  Solar System portal

• Lunar eclipse
• Lunar effect
• Lunar phase
• Near side of the Moon
• Orbit of the Moon

Footnotes

1. The saying "once in a blue moon" meaning "very rarely" is recorded since the 1820s. The term "blue moon" is recorded in 1528, in the couplet Oh churche men are wyly foxes [...] Yf they say the mone is blewe / We must beleve that it is true / Admittynge their interpretacion.^[40]

References

1. "'Super Moon' ExceptIonal Brightest Moon in the Sky of Normandy, Monday, November 14". silvertimes.com. 12 November 2016. from the original on 27 April 2020. Retrieved 8 February 2017.
2. "Moongazers Delight — Biggest Supermoon in Decades Looms Large Sunday Night". 10 November 2016. from the original on 27 April 2020. Retrieved 27 February 2017.
3. [P. Kenneth Seidelmann (ed.), "Phases of the Moon", Explanatory Supplement to the Astronomical Almanac: A Revision to the Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac, (Mill Valley: University Science Books, 1992), p. 478.
4. "What are the names of full moons throughout the year? | Royal Museums Greenwich". www.rmg.co.uk. Retrieved 2023-11-28.
5. Meeus, Jean (1998). "Phases of the Moon". Astronomical Algorithms (2nd ed.). Richmond, Virginia: Willmann-Bell. pp. 349–354. ISBN 0-943396-61-1.
6. Meeus, Jean (2002). "The Duration of the Lunation". More Mathematical Astronomy Morsels. Richmond, Virginia: Willmann-Bell. pp. 19–31. ISBN 0-943396-74-3.
7. Seidelmann, P. Kenneth (2005). "Phases of the Moon". Explanatory Supplement to the Astronomical Almanac. University Science Books. p. 478. ISBN 0-935702-68-7. They are the times when the excess of the Moon's apparent geocentric ecliptic longitude λ_M over the Sun's apparent geocentric ecliptic longitude is 0, 90, 180, or 270 ...
8. . Archived from the original on 7 October 2016. Retrieved 19 September 2016.
9. . Archived from the original on 28 June 2017. Retrieved 19 September 2016.
10. "Vesak 2023: What is it and how do Buddhists celebrate Buddha Day or Wesak?". BBC Newsround. May 15, 2019.
11. . National Geographic News. 6 February 2004. Archived from the original on 24 July 2017. Retrieved 3 December 2005.
12. Gilligan, Stephen G.; Simon, Dvorah (2004). Walking in Two Worlds: The Relational Self in Theory, Practice, and Community. Zeig Tucker & Theisen Publishers. p. 148. ISBN 978-1-932462-11-1.
13. Sappenfield, Mark (13 April 2014). "Blood Moon to arrive Monday night. What is a Blood Moon?". The Christian Science Monitor. from the original on 15 August 2017. Retrieved 8 February 2018.
14. Percy, John (27 September 2010). . University of Toronto. Archived from the original on 3 March 2016. Retrieved 9 January 2015.
15. "What is a Harvest Moon?". Old Farmer's Almanac. from the original on 2017-05-11. Retrieved 2017-05-10.
16. Ferguson, James (1756). Astronomy explained upon Sir Isaac Newton's principles, and made easy to those who have not studied mathematics. p. 128. from the original on 2023-04-09. Retrieved 2016-02-09. ...'harvest moon' is also the cognate of herbist-mānod, the Old High German name of November recorded in Vita Karoli Magni, ch. 29.
17. Neata, Emil. "The Hunter's Moon". Night Sky Info. from the original on 5 November 2020. Retrieved 29 December 2008.
18. . Tippecanoe County Historical Association. Archived from the original on 20 June 2009.
19. Phillips, Tony (22 September 2010). "Watch out for the Super Harvest Moon". NASA Science. from the original on 21 August 2011. Retrieved 13 September 2011.
20. Maddox, Jack (22 September 2010). . CNN. Archived from the original on 18 July 2011. Retrieved 13 September 2011.
21. 1440 minutes / 29.531 days = 50.47 minutes
22. McNish, Larry (2007). "Sunset and Moonrise". RASC Calgary Centre. from the original on 2017-03-17. Retrieved 2016-02-19. This gives a graph showing the effect as seen from Calgary, for the whole of the year 2007.
23. "Full moon dates for 2020, including November's Beaver Moon". The Daily Telegraph. 4 November 2020. from the original on 5 November 2020. Retrieved 9 November 2020.
24. . Farmers' Almanac. Archived from the original on 5 October 2007.{{cite web}}: CS1 maint: bot: original URL status unknown (link) ; . National Geographic. Archived from the original on 20 January 2012. Retrieved 12 January 2012.
25. repeated in The Moon Book by Kim Long (1998:102ff. 2023-04-09 at the Wayback Machine) Also in Llewellyn's 1996 Moon Sign Book (1995)
26. Dance, Scott (23 December 2015). "Long Night's Moon comes on Christmas for first time since 1977". The Baltimore Sun. from the original on 4 July 2017. Retrieved 23 December 2015.
27. "Wolf Moon is the full moon in January". timeanddate.com. from the original on 2018-02-02. Retrieved 2018-01-26.
28. Beard 1918, pp. 78–80. "The Indians' Moons naturally vary in the different parts of the country, but by comparing them all and striking an average as near as may be, the moons are reduced to the following"
29. "Names for the Full Moon". University of Northern Iowa. Retrieved 2023-06-27.
30. "Wolf Moon" is attributed to Algonquian by Haddock (1992); the actual Algonquian name for that moon is squochee kesos or "sun has not strength to thaw". The New England historical & genealogical register and antiquarian journal: v. 10 2023-04-09 at the Wayback Machine The Sioux do mention wolves in their name for January, which means "when wolves run together". American Indian Moons 2012-08-13 at the Wayback Machine; they also refer to that moon as the "moon of the strong cold" or "frost in the teepee". Other tribes had different names for the moons. See also Indian Moons, Days & Other Calendar Stuff, American Indian Moons 2013-04-16 at the Wayback Machine
31. "Why do we have special names for full moons?". Royal Museums Greenwich. Retrieved 2023-06-27.
32. "2014 Chaitra Purnima | Chaitra Pournami date for Amsterdam, North Holland, Netherlands". from the original on 2017-06-10. Retrieved 2014-08-13.
33. "2014 Vaishakha Purnima | Vaishakha Pournami date for Amsterdam, North Holland, Netherlands". from the original on 2017-06-10. Retrieved 2014-08-13.
34. "2014 Guru Purnima | Vyasa Purnima Puja Date and Time for Amsterdam, North Holland, Netherlands". from the original on 2017-06-10. Retrieved 2014-08-13.
35. "Rare Full Moon on Christmas Day, NASA". 16 December 2015. from the original on 2021-05-06. Retrieved 2015-12-23.
36. "Ask Tom: How unusual is a full moon on Christmas Day?". Chicago Tribune. 20 December 2015. from the original on 2017-06-29. Retrieved 2015-12-23.
37. see e.g., Blackburn, Bonnie; et al. (1999). The Oxford Companion to the Year. Oxford University Press. ISBN 0-19-214231-3.
38. Reingold, Edward M.; et al. (2001). Calendrical Calculations: The Millennium Edition. Cambridge University Press. ISBN 0-521-77752-6.
39. Leviticus 23:4–7, 33–35.
40. Wolsey, Thomas (1871). "Rede me and be nott wrothe, for I say no thynge but trothe" (1871 ed.). Birmingham. p. 114.; it isn't clear however if this refers to intercalation.
41. . Farmers' Almanac. 24 August 2009. Archived from the original on 24 January 2018.
42. . Sky and Telescope. 1999. Archived from the original on 27 March 2014. Retrieved 7 October 2009.
43. . 2009-12-23. Archived from the original on 2009-12-23. Retrieved 2022-12-08.

External links

 

Wikimedia Commons has media related to Full moon.

• Moon Phase Calendar for any date