Full moon

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 (more exactly, 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 a circular disk. The full moon occurs roughly once a month.

The time interval between a full (or new) 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.


A full moon is often thought of as an event of a full night's duration. This is somewhat misleading because its phase seen from Earth continuously waxes or wanes (though much too slowly to notice in real time with the naked eye). By definition, its maximum illumination occurs at the moment waxing stops. 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.

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.

On 12 December 2008, the full moon was closer to the Earth than it had been at any time in the previous 15 years. This was referred to in popular media as a supermoon.[4]

On 19 March 2011, there was another full "supermoon", closer to the Earth than at any time in the previous 18 years.[5]

On 14 November 2016, there was another full "supermoon"; this time it was closer to the Earth than at any time in the previous 68 years.[6]





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.[8] See New moon for an explanation of the formula and its parameters.


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.[9][10][11] 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 5.14° 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


Full moon names


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

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.

The "harvest 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, where the term is attributed 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 512 hours after the moment of equinox) for the first time since 1991.[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

The Maine Farmers' Almanac from around the 1930s began to publish Native American "Indian" full moon names. The Farmers' Almanac (since 1955 published in Maine, but not the same publication as the Maine Farmers' Almanac) continues to do so.[23]


  • January: Difficulty, Black Smoke
  • February: Raccoon, Bare Spots on the Ground
  • March: Wind, Little Grass, Sore-Eye
  • April: Ducks, Goose-Eggs
  • May: Green Grass, Root-Food
  • June: Corn-Planting, Strawberry
  • July: Buffalo (Bull), Hot Sun
  • August: Harvest, Cow Buffalo
  • September: Wild Rice, Red Plum
  • October: Leaf-Falling, Nuts
  • November: Deer-Mating, Fur-Pelts
  • December: Wolves, Big Moon


The individual names (some inconsistent) given in Farmers' Almanac, which is not authoritative, include the following:

  • January: "Wolf Moon" (for December in Beard 1918),[26] "Old Moon"
  • February: "Snow Moon", "Hunger Moon"
  • October: "Hunter's Moon", "Blood Moon", "Sanguine Moon"
  • November: "Beaver Moon", "Frosty Moon"

The Long Night's Moon is the last full moon of the year and the one nearest the winter solstice.[27]

"Ice Moon" is also used to refer to the first full moon of January or February.[28]

Hindu full moon festivals


  1. Chaitra Purnima – Gudi Padua, Yugadi, Ugadi, Hanuman Jayanti (April 15, 2014)[29]
  2. Vaishakh Purnima – Narasimh Jayanti, Buddha Jayanthi (Buddha's_Birthday) (May 14, 2014)[30]
  3. Jyeshtha Purnima – Vat Savitri Vrat Vat Purnima (June 8, 2014)[31]
  4. Ashadh Purnima – Guru Purnima, Vyas Purnima (important day for starting education and honoring teachers[31])
  5. Shravan Purnima – Good day for starting Upanayana day, Avani Avittam, Raksha Bandhan. Conceptually Onam also comes on this day.
  6. Bhadrapad Purnima – Start of Pitru Paksha, Madhu Purnima
  7. Ashvin Purnima – Sharad Purnima
  8. Kartik PoornimaKarthikai Deepam festival, Thrukkarthika (in Kerala)
  9. Margasirsha Purnima – Thiruvathira, Dathatreya Jayanthi
  10. Pushya Purnima – Thaipusam, Shakambharee Purnima
  11. Magha Purnima
  12. Phalguna Purnima – Holi

Lunar and lunisolar calendars

Most pre-modern calendars the world over were lunisolar, combining the solar year with the lunation by means of intercalary months.[34][35] 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.[36]

Intercalary months


Blue moon

In the modern system of "traditional" 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).[37]

According to the Farmers' Almanac, a "blue moon" is the third full moon in any period between either solstice and equinox, or between equinox and solstice, (calculated using the mean tropical year), which contains four full moons.[38] 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 seasons began at 1:48 am on 23 March, 9:15 am on 22 June, 4:42 pm on 21 September and 12:10 am on 22 December, while the astronomical seasons began at 4:39 am on 21 March, 11:09 pm on 21 June, 2:42 pm on 23 September and 10:30 am on 22 December (all times GMT). Due to a misinterpretation of this definition in the March 1946 Sky & Telescope magazine, "blue moon" has also been used in the sense of "the second full moon in any month which contains two full moons (this usage has been noted as "erroneous" by Sky & Telescope in 1999).[39] According to either definition, "blue moons" occur with the average frequency of intercalary months, seven times in 19 years, the Farmers' Almanac system of "full moon names" effectively defining a lunisolar calendar.

See also


  3. [P. Kenneth Seidelmann (ed.), [https://archive.org/details/131123ExplanatorySupplementAstronomicalAlmanac/page/n253 "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.
  10. "Celestial Alignment without Lunar Eclipse; from google (full moon earth block sunlight) result 2".
  12. "Full Moon Effect On Behavior Minimal, Studies Say". National Geographic News. 6 February 2004.
  13. Sappenfield, Mark (13 April 2014). "Blood Moon to arrive Monday night. What is a Blood Moon?". Christian Science Monitor. Retrieved 8 February 2018.
  15. "What is a Harvest Moon?". Old Farmer's Almanac.
  16. Ferguson, James (1756). Astronomy explained upon Sir Isaac Newton's principles, and made easy to those who have not studied mathematics. p. 128. ..."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. Retrieved 29 December 2008.
  21. 1440 minutes / 29.531 days = 50.47 minutes
  22. McNish, Larry (2007). "Sunset and Moonrise". RASC Calgary Centre. This gives a graph showing the effect as seen from Calgary, for the whole of the year 2007.
  23. "Full Moon Names and Their Meanings". Farmers' Almanac. Archived from the original on 2007-10-05.CS1 maint: BOT: original-url status unknown (link) (); "Full Moons: What's in a Name?". National Geographic. Retrieved 12 January 2012.
  24. Beard 1918, pp. 7880. "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"
  27. Dance, Scott (December 23, 2015). "'Long Night's Moon' comes on Christmas for first time since 1977". Baltimore Sun.
  28. https://www.timeanddate.com/astronomy/moon/wolf.html
  32. Rare Full Moon on Christmas Day, NASA
  33. Ask Tom: How unusual is a full moon on Christmas Day?
  36. Leviticus 23:4-7, 33-35.
  38. Farmers' Almanac, "What is a blue moon?", 24 August 2009, available at .
  39. Sky and Telescope "What's a blue moon?"