Month
20354
223500170
2008-07-04T09:54:00Z
JAnDbot
1725149
robot Removing: [[cr:Kâ-isiwepahki]] Modifying: [[be-x-old:Месяц (адзінка вымярэньня часу)]], [[fa:ماه (زمان)]]
{{for|the Egyptian hawk-god|Menthu}}
{{wiktionary}}
The '''month''' is a unit of [[time]], used with [[calendar]]s, which is approximately as long as some natural [[Orbital period|period]] related to the motion of the [[Moon]]; ''month'' and ''Moon'' are [[cognate]]s. The traditional concept arose with the cycle of [[moon phase]]s; such months (lunations) are [[#Synodic month|synodic months]] and last approximately 29.53 [[day]]s. From [[excavation|excavated]] [[tally stick]]s, researchers have deduced that people counted days in relation to the Moon's phases as early as the [[Paleolithic]] age. Synodic months are still the basis of many calendars today.
==Astronomical background==
In the Neolithic times of Predynastic Egypt, each of the 12 [[Egyptian calendar|Egyptian months]] began with the first New Moon following the appearance of [[Sirius]] at sunrise (The Egyptian hieroglyphic symbol for "month" was a crescent of the new moon over a star).
The [[Hellenic calendars]], the [[Hebrew calendar|Hebrew Lunisolar calendar]] and the [[Islamic calendar|Islamic Lunar calendar]] also started the month with the first appearance of the thin crescent of the [[new moon]].
However, the motion of the Moon in its [[orbit]] is very complicated and its period is not constant. The date and time of this actual observation depends on the exact geographical longitude as well as latitude, atmospheric conditions, the visual acuity of the observers, etc. Therefore the beginning and lengths of months in these calendars can not be accurately predicted.
Today, while some like the [[Karaites]] Jews still rely on actual moon observations, most people use the [[Gregorian calendar|Gregorian solar calendar]].
===Sidereal month===
The period of the Moon's orbit as defined with respect to the [[celestial sphere]] is known as a ''sidereal'' month because it is the time it takes the Moon to return to a given position among the [[star]]s ({{lang-la|sidus}}): 27.321661 days (27 d 7 h 43 min 11.5 s). This type of month has been observed among cultures in the Middle East, India, and China in the following way: they divided the sky into 27 or 28 [[lunar mansion]]s, defined by [[asterism (astronomy)|asterism]]s (apparent groups of stars), one for each day of the sidereal month.
===Tropical month===
It is customary to specify positions of celestial bodies with respect to the vernal [[equinox]]. Because of [[precession]], this point moves back slowly along the [[ecliptic]]. Therefore it takes the Moon less time to return to an ecliptic longitude of zero than to the same point amidst the fixed stars: 27.321582 days (27 d 7 h 43 min 4.7 s). This slightly shorter period is known as ''tropical'' month; cf. the analogous [[tropical year]] of the [[Sun]].
===Anomalistic month===
Like all orbits, the [[Orbit of the Moon|Moon's orbit]] is an ellipse rather than a circle. However, the orientation (as well as the shape) of this orbit is not fixed. In particular, the position of the extreme points (the line of the [[Apsis|apsides]]: [[perigee]] and [[apogee]]), makes a full circle ([[lunar precession]]) in about nine years. It takes the Moon longer to return to the same apsis because it moved ahead during one revolution. This longer period is called the ''anomalistic'' month, and has an average length of 27.554551 days (27 d 13 h 18 min 33.2 s). The apparent diameter of the Moon varies with this period, and therefore this type has some relevance for the prediction of [[eclipse]]s (see [[Saros]]), whose extent, duration, and appearance (whether total or annular) depend on the exact apparent diameter of the Moon. The apparent diameter of the [[full moon]] varies with the [[full moon cycle]] which is the beat period of the synodic and anomalistic month, and also the period after which the apsides point to the Sun again.
===Draconic month===
Also called the nodical month. The orbit of the moon lies in a plane that is tilted with respect to the plane of the ecliptic: it has an [[inclination]] of about five degrees. The line of intersection of these planes defines two points on the celestial sphere: the [[ascending node]], when the moon's path crosses the ecliptic as the moon moves into the northern hemisphere, and [[descending node]] when the moon's path crosses the ecliptic as the moon moves into the southern hemisphere. The draconic or nodical month is the average interval between two successive transits of the moon through its ascending node. Because of the sun's gravitational pull on the moon, the moon's orbit gradually rotates westward on its axis, which means the nodes gradually rotate around the earth. As a result, the time it takes the moon to return to the same node is shorter than a sidereal month. It lasts 27.212220 days (27 d 5 h 5 min 35.8 s). The plane of the moon's orbit [[precession|precesses]] over a full circle in about 18.6 years.
Because the moon's orbit is inclined with respect to the ecliptic, the sun, moon, and earth are in line only when the moon is at one of the nodes. Whenever this happens a solar or lunar [[eclipse]] is possible. The name "draconic" refers to a mythical dragon, said to live in the nodes and eat the sun or moon during an eclipse.
===Synodic month===
This is the average period of the Moon's revolution with respect to the sun. The synodic month is responsible for the moon's [[lunar phase|phases]], because the Moon's appearance depends on the position of the Moon with respect to the Sun as seen from the Earth. While the moon is orbiting the earth, the Earth is progressing in its orbit around the Sun. This means that after completing a sidereal month the Moon must move a little farther to reach the new position of the Earth with respect to the Sun. This longer period is called the ''synodic'' month from the Greek ''{{lang|el-Latn|syn hodô}}'' ({{lang|el|σὺν ὁδῴ}}), meaning "with the way [of the sun]". Because of perturbations in the orbits of the Earth and Moon, the actual time between [[lunation]]s may range from about 29.27 to about 29.83 days. The long-term average duration is 29.530589 days (29 d 12 h 44 min 2.9 s). The synodic month is used in the [[Metonic cycle]].
===Month lengths===
Here is a list of the average length of the various astronomical lunar months <ref>Derived from ELP2000-85: M. Chapront-Touzé, J. Chapront (1991): ''Lunar tables and programs from 4000 B. C. to A. D. 8000''. Willmann-Bell, Richmond VA; ISBN 0-943396-33-6</ref>. These are not constant, so a first-order (linear) approximation of the secular change is provided:
Valid for the epoch [[J2000.0]] (1 Jan. 2000 12:00 [[Terrestrial Time|TT]]):
{| border="1" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 95%;"
|-
| sidereal month
| 27.321661547 + 0.000000001857 × y days
|-
| tropical month
| 27.321582241 + 0.000000001506 × y days
|-
| anomalistic month
| 27.554549878 − 0.000000010390 × y days
|-
| draconic month
| 27.212220817 + 0.000000003833 × y days
|-
| synodic month
| 29.530588853 + 0.000000002162 × y days
|}
''Note:'' time expressed in [[Ephemeris Time]] (more precisely [[Terrestrial Time]]) with days of 86,400 [[SI]] [[second]]s. '''y''' is years since the epoch (2000), expressed in Julian years of 365.25 days. Note that for calendrical calculations, one would probably use days measured in the time scale of [[Universal Time]], which follows the somewhat unpredictable rotation of the Earth, and progressively accumulates a difference with ephemeris time called [[Delta T|ΔT]].
==Calendrical consequences==
:''For more details on this topic, see [[lunar calendar]] and [[lunisolar calendar]].''
At the simplest level, all lunar calendars are based on the approximation that 2 lunations last 59 days: a 30 day '''full month''' followed by a 29 day '''hollow month''' — but this is only marginally accurate and quickly needs correction by using larger cycles, or the equivalent of [[leap day]]s.
Second, the synodic month does not fit easily into the [[year]], which makes constructing accurate, rule-based lunisolar calendars difficult. The most common solution to this problem is the [[Metonic cycle]], which takes advantage of the fact that 235 lunations are approximately 19 [[tropical year]]s (which add up to not quite 6940 days). However, a Metonic calendar (such as the [[Hebrew calendar]]) will drift against the seasons by about 1 day every 200 years.
The problems of creating reliable lunar calendars may explain why [[solar calendar]]s, having months which no longer relate to the phase of the moon, and being based only on the motion of the sun against the sky, have generally replaced lunar calendars for civil use in most societies.
==Months in various calendars==
===Julian and Gregorian calendars===
The [[Gregorian calendar]], like the [[Julian calendar]] before it, has twelve months:
#[[January]], 31 [[day]]s
#[[February]], 28 days, 29 in [[leap year]]s
#[[March]], 31 days
#[[April]], 30 days
#[[May]], 31 days
#[[June]], 30 days
#[[July]], 31 days
#[[August]], 31 days
#[[September]], 30 days
#[[October]], 31 days
#[[November]], 30 days
#[[December]], 31 days
{{selfref|One of Wikipedia's sister projects, [[Wiktionary]], provides translations of each of the Gregorian/Julian calendar months into a dozen or more languages. Month-by-month links are provided here: [[wikt:January|January]], [[wikt:February|February]], [[wikt:March|March]], [[wikt:April|April]], [[wikt:May|May]], [[wikt:June|June]], [[wikt:July|July]], [[wikt:August|August]], [[wikt:September|September]], [[wikt:October|October]], [[wikt:November|November]], [[wikt:December|December]].}}
The average month in the Gregorian calendar has a length of 30.4167 days or 4.345 weeks in a non-leap year and 30.5 days or 4.357 weeks in a leap year, or 30.436875 days in a mean Gregorian month overall (365.2425 ÷ 12).
Months existing in the [[Roman calendar]] in the past include:
*[[Mercedonius]], an occasional month after February to realign the calendar.
*[[Quintilis]], renamed to July in honour of [[Julius Caesar]].
*[[Sextilis]], renamed to August in honour of [[Augustus]].
The famous [[mnemonic]] ''[[Thirty days hath September]]'' is the most common way of teaching the lengths of the months in the English-speaking world.
[[Image:Month - Knuckles (en).svg|thumb|300px|On top of the knuckles (yellow): 31 days<br />Between the knuckles (blue): 30 days<br />[[February]] (red) has 28 or 29 days.]]
The knuckles of the four fingers of one's hand and the spaces between them can be used to remember the lengths of the months. By making a fist, each month will be listed as one proceeds across the hand. All months landing on a knuckle are 31 days long and those landing between them are not. When the knuckle of the index finger is reached (July), go back to the first knuckle (or over to the first knuckle on the other fist, held next to the first) and continue with August. This physical mnemonic has been taught to primary school students for many decades.<ref>[http://www.eudesign.com/mnems/dayspcm.htm Days in each month]</ref><ref>[http://www.education-world.com/a_lesson/lesson045.shtml Happy New Year! Or is it? by Education World]</ref><ref>[http://psychology.hypnoticworld.com/memory/mnemonics.php Mnemonics to improve memory]</ref><ref>[http://www.fullbooks.com/The-Boy-Mechanic-Volume-17.html The Boy Mechanic: A Handy Calendar] (1913) from [[Project Gutenberg]]</ref>
====Calends, nones, and ides====
The '''[[ides]]''' occur on the thirteenth day in eight of the months, but in March, May, July, and October, they occur on the fifteenth. The '''[[nones]]''' always occur 8 days before the ides, i.e., on the fifth or the seventh. The '''[[calends]]''' are always the first day of the month.
===Hebrew Calendar===
The [[Hebrew calendar]] has 12 or 13 months.
# [[Nisan]], 30 days ניסן
# [[Iyyar]], 29 days אייר
# [[Sivan]], 30 days סיון
# [[Tammuz]], 29 days תמוז
# [[Av]], 30 days אב
# [[Elul]], 29 days אלול
# [[Tishri]], 30 days תשרי
# [[Heshvan]], 29/30 days חשון
# [[Kislev]], 29/30 days כסלו
# [[Tevet]], 29 days טבת
# [[Shevat]], 30 days שבת
# [[Adar 1]], 30 days, [[Intercalation|intercalary]] month אדר א
# [[Adar 2]], 29 days אדר ב
Adar 1 is only added 7 times in 19 years. In ordinary years, Adar 2 is simply called Adar.
===French Republican calendar===
{{main|French Republican calendar}}
This calendar was proposed during the French Revolution, and used by the French government for about twelve years from late 1793. There were twelve months of 30 days each, grouped into three ten-day weeks called ''décades''. The five or six extra days needed to approximate the tropical year were placed after the months at the end of each year. A period of four years ending on a leap day was to be called a ''Franciade''. It began at the autumn equinox:
*Autumn:
#[[Vendémiaire]]
#[[Brumaire]]
#[[Frimaire]]
*Winter:
#[[Nivôse]]
#[[Pluviôse]]
#[[Ventôse]]
*Spring:
#[[Germinal (French Republican Calendar)|Germinal]]
#[[Floréal]]
#[[Prairial]]
*Summer:
#[[Messidor]]
#[[Thermidor]]
#[[Fructidor]]
===Islamic calendar===
There are also twelve months in the [[Islamic calendar]]. They are named as follows:
# [[Muharram|Muharram ul Haram]] (or shortened to Muharram) محرّم
# [[Safar]] صفر
# [[Rabi`-ul-Awwal]] (Rabi' I) ربيع الأول
# [[Rabi`-ul-Akhir]] (or Rabi` al-Tיhaany) (Rabi' II) ربيع الآخر أو ربيع الثاني
# [[Jumaada-ul-Awwal]] (Jumaada I) جمادى الأول
# [[Jumaada-ul-Akhir]] (or Jumaada al-Thaany) (Jumaada II) جمادى الآخر أو جمادى الثاني
# [[Rajab]] رجب
# [[Sha'aban]] شعبان
# [[Ramadan (calendar month)|Ramadhan]] رمضان
# [[Shawwal]] شوّال
# [[Dhul Qadah]] (or Thw al-Qi`dah) ذو القعدة
# [[Dhul Hijja]] (or Thw al-Hijjah) ذو الحجة
===Hindu Calendar===
The [[Hindu Calendar]] has various systems of naming the months. The months in the lunar calendar are:
# [[Chaitra]]
# [[Vaishakha|Vaishaakha]]
# [[Jyeshtha|Jyaishtha]]
# [[Aashaadha]]
# [[Shraavana]]
# [[Bhaadrapada]]
# [[Aashvina|Aashvayuja]]
# [[Kaartika]]
# [[Maargashiirsha]]
# [[Pausha]]
# [[Maagha]]
# [[Phaalguna]]
These are also the names used in the [[Indian national calendar]] for the newly redefined months.
The names in the solar calendar are just the names of the [[zodiac]] sign in which the sun travels. They are
<!-- surely this table can be done differently/better? -->
# [[Aries (constellation)|Mesha]]
# [[Taurus (constellation)|Vrishabha]]
# [[Gemini (constellation)|Mithuna]]
# [[Cancer (constellation)|Kataka]]
# [[Leo (constellation)|Simha]]
# [[Virgo (constellation)|Kanyaa]]
# [[Libra (constellation)|Tulaa]]
# [[Scorpius (constellation)|Vrishcika]]
# [[Sagittarius (constellation)|Dhanus]]
# [[Capricornus (constellation)|Makara]]
# [[Aquarius (constellation)|Kumbha]]
# [[Pisces (constellation)|Miina]]
===[[Tamil calendar]]===
# Chitirai
# Vaikasi
# Aani
# Aadi
# Aavani
# Purratasi
# Aiypasi
# Kaarthigai
# Maargazhi
# Thai
# Maasi
# Panguni
===[[Sinhala calendar]]===
# Duruthu
# Nawam
# Madin
# Bak (Sihala and Hindu New Year)
# Vesak
# Poson
# Asela
# Nikini
# Binara
# Vap
# Iil
# Unduwap
===Iranian/Persian calendar===
The [[Iranian calendar|Iranian / Persian calendar]], currently used in [[Iran]] and [[Afghanistan]], also has 12 months. The [[Persian language|Persian]] names are included in the parentheses.
# [[Farvardin]] (فروردین), 31 days
# [[Ordibehesht]] (اردیبهشت), 31 days
# [[Khordad]] (خرداد), 31 days
# [[Tir (month)|Tir]] (تیر), 31 days
# [[Mordad]] (مرداد), 31 days
# [[Shahrivar]] (شهریور), 31 days
# [[Mehr]] (مهر), 30 days
# [[Aban]] (آبان), 30 days
# [[Azar]] (آذر), 30 days
# [[Dey]] (دی), 30 days
# [[Bahman]] (بهمن), 30 days
# [[Esfand]] (اسفند), 29 days, 30 in leap years
===Icelandic/Old Norse calendar===
The old Icelandic calendar is not in official use anymore, but some Icelandic holidays and annual feasts are still calculated from it. It has 12 months, broken down into two groups of six often termed "winter months" and "summer months". The calendar is peculiar in that the months always start on the same [[weekday]] rather than on the same [[calendar date|date]]. Hence [[Þorri]] always starts on a Friday sometime between [[January 19]] and [[January 25]] ''<small>([[Julian calendar|Old style]]: [[January 9]] to [[January 15]])</small>'' , [[Góa]] always starts on a Sunday between [[February 18]] and [[February 24]] ''<small>([[Julian calendar|Old style]]: [[February 8]] to [[February 14]])</small>''.
* Skammdegi ("Short days")
# [[Gormánuður]] (mid October - mid November, "slaughter month" or "[[Gór]]'s month")
# [[Ýlir]] (mid November - mid December, "[[Yule]] month")
# [[Mörsugur]] (mid December - mid January, "fat sucking month")
# [[Þorri]] (mid January - mid February, "frozen snow month")
# [[Góa]] (mid February - mid March, "Góa's month, see [[Nór]]")
# [[Einmánuður]] (mid March - mid April, "lone" or "single month")
* Náttleysi ("Nightless days")
# [[Harpa]] (mid April - mid May, Harpa is a female name, probably a forgotten goddess, first day of Harpa is celebrated as [[Sumardagurinn fyrsti]] - first day of summer)
# [[Skerpla]] (mid May - mid June, another forgotten goddess)
# [[Sólmánuður]] (mid June - mid July, "[[sun]] month")
# [[Heyannir]] (mid July - mid August, "[[hay]] business month")
# [[Tvímánuður]] (mid August - mid September, "two" or "second month")
# [[Haustmánuður]] (mid September - mid October, "autumn month")
===Old Hungarian calendar===
Historically Hungary used a 12-month calendar that appears to have been zodiacal in nature<ref>[http://users.tpg.com.au/etr/rovas/marsigli.html The Calendar by Marsigli: the ancient Hungarian Calendar<!-- Bot generated title -->]</ref> but eventually came to correspond to the Gregorian months as shown below<ref>[http://www.freeweb.hu/magyarcsaladok/honapok_nevei.htm Hónapok nevei<!-- Bot generated title -->]</ref>:
# Boldogasszony hava (January, ‘month of the happy/blessed lady’)
# Böjtelő hava (February, ‘month of early fasting/Lent’ or ‘month before fasting/Lent’)
# Böjtmás hava (March, ‘second month of fasting/Lent’)
# Szent György hava (April, ‘St. George’s month)
# Pünkösd hava (May, ‘Pentecost month’)
# Szent Iván hava (June, ‘St. Ivan’s month’)
# Szent Jakab hava (July, ‘St. James’ month’)
# Kisasszony hava (August, ‘month of the young lady [Blessed Virgin]’)
# Szent Mihály hava (September, ‘St. Michael’s month’)
# Mindszent hava (October, ‘all saints month’)
# Szent András hava (November, ‘St. Andrew’s month’)
# Karácsony hava (December, ‘month of Yule/Christmas’)
===Old Egyptian calendar===
The ancient civil Egyptian calendar had a year that was 365 days long and was divided into 12 months of 30 days each, plus 5 extra days (epagomenes) at the end of the year. The months were divided into 3 "weeks" of ten days each. Because the ancient Egyptian year was almost a quarter of a day shorter than the solar year and stellar events "wandered" through the calendar, it is referred to as Annus Vagus or "Wandering Year".
#Thout
#Paopi
#Hathor
#Koiak
#Tooba
#Emshir
#Paremhat
#Paremoude
#Pashons
#Paoni
#Epip
#Mesori
==See also==
* [[Table of lunar month correspondences]]
* [[Maya calendar]]
* [[Chinese calendar]]
* [[Egyptian calendar|Egyptian Calendar]]
==Notes==
{{reflist}}
{{Time Topics}}
{{Time measurement and standards}}
[[Category:Units of time]]
[[Category:Calendars]]
[[Category:Orbit of the Moon]]
[[als:Monat]]
[[ang:Mōnaþ]]
[[ar:شهر]]
[[arc:ܝܪܚܐ]]
[[ast:Mes]]
[[zh-min-nan:Goe̍h]]
[[be-x-old:Месяц (адзінка вымярэньня часу)]]
[[bs:Mjesec (period)]]
[[bg:Месец]]
[[ca:Mes]]
[[cv:Уйăх]]
[[ceb:Bulan (panahon)]]
[[cs:Kalendářní měsíc]]
[[da:Måned]]
[[de:Monat]]
[[eml:Més]]
[[es:Mes]]
[[eo:Monato]]
[[eu:Hilabete]]
[[fa:ماه (زمان)]]
[[fr:Mois]]
[[fy:Moanne (tiid)]]
[[fur:Mês]]
[[gl:Mes sinódico]]
[[ko:달 (시간)]]
[[hi:मास]]
[[hsb:Měsac]]
[[hr:Mjesec (period)]]
[[io:Monato]]
[[id:Bulan (penanggalan)]]
[[ia:Mense]]
[[is:Mánuður]]
[[it:Mese]]
[[he:חודש]]
[[kl:Qaammat]]
[[kn:ತಿಂಗಳು]]
[[ka:თვე]]
[[kk:Ай]]
[[kw:Mis]]
[[sw:Mwezi (wakati)]]
[[kg:Ngonda (manaka)]]
[[ht:Mwa]]
[[ku:Meh]]
[[lad:Mez]]
[[lo:ເດືອນ]]
[[la:Mensis]]
[[lv:Mēnesis]]
[[lt:Mėnuo]]
[[ln:Sánzá (ntángo)]]
[[jbo:masti]]
[[hu:Hónap]]
[[mk:Месец]]
[[mi:Marama (maramataka)]]
[[my:Months]]
[[nl:Maand]]
[[ja:月 (暦)]]
[[no:Måned]]
[[nn:Månad]]
[[nrm:Mais]]
[[oc:Mes]]
[[nds:Maand (Tiet)]]
[[pl:Miesiąc]]
[[pt:Mês]]
[[ksh:Moohnd (Kalländo)]]
[[ro:Lună (timp)]]
[[rmy:Chhon (bersheski)]]
[[qu:Killa pacha]]
[[ru:Месяц]]
[[se:Mánotbadji]]
[[sq:Muaji]]
[[simple:Month]]
[[ss:Ínyangá]]
[[sk:Mesiac (časová jednotka)]]
[[sl:Mesec]]
[[so:Bilaha]]
[[sr:Месеци]]
[[sh:Mjesec (jedinica)]]
[[fi:Kuukausi]]
[[sv:Månad]]
[[tl:Buwan (panahon)]]
[[ta:மாதம்]]
[[tt:Ay]]
[[th:เดือน]]
[[tpi:Mun (taim)]]
[[tr:Ay (zaman)]]
[[uk:Місяць (календарний)]]
[[fiu-vro:Kuu (aomõõt)]]
[[yi:מאנאט]]
[[yo:Osù]]
[[cbk-zam:Mes]]
[[zh:月]]