Month

The Hellenic calendars, the Hebrew Lunisolar calendar and the Islamic Lunar calendar 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 defined by observation cannot be accurately predicted.

While some like the Jewish Karaites still rely on actual moon observations, most people use the Gregorian solar calendar.

Pingelapese, a language from Micronesia, also uses a lunar calendar. There are 12 months associated with their calendar. The moon first appears in March, they name this month Kahlek. This system has been used for hundreds of years and throughout many generations. This calendar is cyclical and relies on the position and shape of the moon.[1]

The Gregorian calendar, like the Julian calendar before it, has twelve months:

On top of the knuckles (yellow): 31 days
Between the knuckles (blue): 30 days
February (red) has 28 or 29 days.

The white keys of the musical keyboard correlate to months with 31 days. ('F' corresponds to January.)

The mean month length of the Gregorian calendar is 30.436875 days.

Months of the historical Roman calendar included:

• the mensis intercalaris, 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 a common way of teaching the lengths of the months in the English-speaking world. Any five consecutive months (not including February) contain 153 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.[2][3]

This cyclical pattern of month lengths matches the musical keyboard alternation of white and black keys (with the note 'F' correlating to the month of January).

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 (one Roman week) before the ides, i.e., on the fifth or the seventh. The calends are always the first day of the month, and before Julius Caesar's reform fell sixteen days (two Roman weeks) after the ides (except the ides of February and the intercalary month).

Within a month, the following dates fall on the same weekday:

• 01, 08, 15, 22, and 29 (e.g., in January 2019, all these dates fell on a Tuesday)
• 02, 09, 16, 23, and 30 (e.g., in January 2019, all these dates fell on a Wednesday)
• 03, 10, 17, 24, and 31 (e.g., in January 2019, all these dates fell on a Thursday)
• 04, 11, 18, and 25 (e.g., in January 2019, all these dates fell on a Friday)
• 05, 12, 19, and 26 (e.g., in January 2019, all these dates fell on a Saturday)
• 06, 13, 20, and 27 (e.g., in January 2019, all these dates fell on a Sunday)
• 07, 14, 21, and 28 (e.g., in January 2019, all these dates fell on a Monday)

Some months have the same date/weekday structure.

In a non-leap year:

• January/October (e.g., in 2019, they began/begin on a Tuesday)
• February/March/November (e.g., in 2019, they began/begin on a Friday)
• April/July (e.g., in 2019, they began/begin on a Monday)
• September/December (e.g., in 2019, they begin on a Sunday)
• January 1 and December 31 fall on the same weekday (e.g. in 2019 on a Tuesday)

In a leap year:

• February/August (e.g. in 2020, they begin on a Saturday)
• March/November (e.g., in 2020, they begin on a Sunday)
• January/April/July (e.g., in 2020, they begin on a Wednesday)
• September/December (e.g., in 2020, they begin on a Tuesday)
• February 29 (the leap day) falls on the same weekday like February 1, 08, 15, 22, and August 1 (see above; e.g. in 2020 on a Saturday)

The Hebrew calendar has 12 or 13 months.

1. Nisan, 30 days ניסן
2. Iyar, 30 days אייר
3. Sivan, 30 days סיון
4. Tammuz, 29 days תמוז
5. Av, 30 days אב
6. Elul, 29 days אלול
7. Tishri, 30 days תשרי
8. Marcheshvan, 29/30 days מַרְחֶשְׁוָן
9. Kislev, 30/29 days כסלו
10. Tevet, 29 days טבת
11. Shevat, 30 days שבט
12. Adar 1, 30 days, intercalary month אדר א
13. 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.

There are also twelve months in the Islamic calendar. They are named as follows:

1. Muharram (Restricted/sacred) محرّم
2. Safar (Empty/Yellow) صفر
3. Rabī' al-Awwal/Rabi' I (First Spring) ربيع الأول
4. Rabī' ath-Thānī/Rabi' al-Aakhir/Rabi' II (Second spring or Last spring) ربيع الآخر أو ربيع الثاني
5. Jumada al-Awwal/Jumaada I (First Freeze) جمادى الأول
6. Jumada ath-Thānī or Jumādā al-Thānī/Jumādā II (Second Freeze or Last Freeze) جمادى الآخر أو جمادى الثاني
7. Rajab (To Respect) رجب
8. Sha'bān (To Spread and Distribute) شعبان
9. Ramadān (Parched Thirst) رمضان
10. Shawwāl (To Be Light and Vigorous) شوّال
11. Dhu al-Qi'dah (The Master of Truce) ذو القعدة
12. Dhu al-Hijjah (The Possessor of Hajj) ذو الحجة

See Islamic calendar for more information on the Islamic calendar.

The Hindu calendar has various systems of naming the months. The months in the lunar calendar are:

These are also the names used in the Indian national calendar for the newly redefined months. Purushottam Maas or Adhik Maas (translit. adhika = 'extra', māsa = 'month') is an extra month in the Hindu calendar that is inserted to keep the lunar and solar calendars aligned. "Purushottam" is an epithet of Vishnu, to whom the month is dedicated.

The names in the solar calendar are just the names of the zodiac sign in which the sun travels. They are

1. Mesha
2. Vrishabha
3. Mithuna
4. Kataka
5. Simha
6. Kanyaa
7. Tulaa
8. Vrishcika
9. Dhanus
10. Makara
11. Kumbha
12. Miina

The Baháʼí calendar is the calendar used by the Baháʼí Faith. It is a solar calendar with regular years of 365 days, and leap years of 366 days. Years are composed of 19 months of 19 days each (361 days), plus an extra period of "Intercalary Days" (4 in regular and 5 in leap years).[4] The months are named after the attributes of God. Days of the year begin and end at sundown.[4]

The Iranian / Persian calendar, currently used in Iran and Afghanistan, also has 12 months. The Persian names are included in the parentheses. It begins on the northern Spring equinox.

1. Farvardin (31 days, فروردین)
2. Ordibehesht (31 days, اردیبهشت)
3. Khordad (31 days, خرداد)
4. Tir (31 days, تیر)
5. Mordad (31 days, مرداد)
6. Shahrivar (31 days, شهریور)
7. Mehr (30 days, مهر)
8. Aban (30 days, آبان)
9. Azar (30 days, آذر)
10. Dey (30 days, دی)
11. Bahman (30 days, بهمن)
12. Esfand (29 days- 30 days in leap year, اسفند)

The Bangla calendar, used in Bangladesh, follows solar months and it has six seasons. The months and seasons in the calendar are:

The months in the Nanakshahi calendar are:[5]

Like the Hindu calendar, the Khmer calendar consists of both a lunar calendar and a solar calendar. The solar is used more commonly than the lunar calendar. There are 12 months and the numbers of days follow the Julian and Gregorian calendar.

The Khmer lunar calendar contains 12 months; however, the eighth month is repeated (as a "leap month") every two or three years, making 13 months instead of 12.[6]

• មិគសិរ
• បុស្ស
• មាឃ
• ផល្គុន
• ចេត្រ
• វិសាខ/ ពិសាខ
• ជេស្ឋ
• ឤសាឍ, or in the case of a year with a leap month:
  • បឋមសាឍ
  • ទុតិយាសាឍ
• ស្រាពណ៍
• ភទ្របទ
• អស្សុជ
• កត្តិក

The Tongan calendar is based on the cycles of the moon around the earth in one year. The months are:

1. Liha Mu'a
2. Liha Mui
3. Vai Mu'a
4. Vai Mui
5. Faka'afu Mo'ui
6. Faka'afu Mate
7. Hilinga Kelekele
8. Hilinga Mea'a
9. 'Ao'ao
10. Fu'ufu'unekinanga
11. 'Uluenga
12. Tanumanga
13. 'O'oamofanongo

The Sinhalese calendar is the Buddhist calendar in Sri Lanka with Sinhala names. Each full moon Poya day marks the start of a Buddhist lunar month.[7] The first month is Vesak.[8]

1. Duruthu (දුරුතු)
2. Navam (නවම්)
3. Mædin (මැදින්)
4. Bak (බක්)
5. Vesak (වෙසක්)
6. Poson (පොසොන්)
7. Æsala (ඇසල)
8. Nikini (නිකිණි)
9. Binara (බිනර)
10. Vap (වප්)
11. Il (iL) (ඉල්)
12. Unduvap (උඳුවප්)

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 date. Hence Þorri always starts on a Friday sometime between January 22 and January 28 (Old style: January 9 to January 15), Góa always starts on a Sunday between February 21 and February 27 (Old style: February 8 to February 14).

• Skammdegi ("Short days")

1. Gormánuður (mid-October – mid-November, "slaughter month" or "Gór's month")
2. Ýlir (mid-November – mid-December, "Yule month")
3. Mörsugur (mid-December – mid-January, "fat sucking month")
4. Þorri (mid-January – mid-February, "frozen snow month")
5. Góa (mid-February – mid-March, "Góa's month, see Nór")
6. Einmánuður (mid-March – mid-April, "lone" or "single month")

• Náttleysi ("Nightless days")

1. 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)
2. Skerpla (mid-May – mid-June, another forgotten goddess)
3. Sólmánuður (mid-June – mid-July, "sun month")
4. Heyannir (mid-July – mid-August, "hay business month")
5. Tvímánuður (mid-August – mid-September, "two" or "second month")
6. Haustmánuður (mid-September – mid-October, "autumn month")

*NOTE: New Year in ancient Georgia started from September.

1. Torsmånad (January, 'Torre's month' (ancient god))
2. Göjemånad (February, 'Goe's month' (ancient goddess))
3. Vårmånad (March, 'Spring month')
4. Gräsmånad (April, 'Grass month')
5. Blomstermånad (May, 'Bloom month')
6. Sommarmånad (June, 'Summer month')
7. Hömånad (July, 'Hay month')
8. Skördemånad, Rötmånad (August, 'Harvest month' or 'Rot month')
9. Höstmånad (September, 'Autumn month')
10. Slaktmånad (October, 'Slaughter month')
11. Vintermånad (November, 'Winter month')
12. Julmånad (December, 'Christmas month')

Like the Old Norse calendar, the Anglo-Saxons had their own calendar before they were Christianized which reflected native traditions and deities. These months were attested by Bede in his works On Chronology and The Reckoning of Time written in the 8th century.[9] His months are probably those as written in the Northumbrian dialect of Old English with which he was familiar. The months were so named after the moon; the new moon marking the end of an old month and start of a new month; the full moon occurring in the middle of the month, after which the month was named.

1. Æfterra-ġēola mōnaþ (January, 'After-Yule month')
2. Sol-mōnaþ (February, 'Sol month')
3. Hrēð-mōnaþ (March, 'Hreth month')
4. Ēostur-mōnaþ (April, 'Ēostur month')
5. Ðrimilce-mōnaþ (May, 'Three-milkings month')
6. Ærra-Liþa (June, 'Ere-Litha')
7. Æftera-Liþa (July, 'After-Litha')
8. Weōd-mōnaþ (August, 'Weed month')
9. Hāliġ-mōnaþ or Hærfest-mōnaþ (September, 'Holy month' or 'Harvest month')
10. Winter-fylleþ (October, 'Winter-filleth')
11. Blōt-mōnaþ (November, 'Blót month')
12. Ærra-ġēola mōnaþ (December, 'Ere-Yule')

Nagyszombati kalendárium (in Latin: Calendarium Tyrnaviense) from 1579. Historically Hungary used a 12-month calendar that appears to have been zodiacal in nature[10] but eventually came to correspond to the Gregorian months as shown below:[11]

1. Boldogasszony hava (January, 'month of the happy/blessed lady')
2. Böjtelő hava (February, 'month of early fasting/Lent' or 'month before fasting/Lent')
3. Böjtmás hava (March, 'second month of fasting/Lent')
4. Szent György hava (April, 'Saint George's month')
5. Pünkösd hava (May, 'Pentecost month')
6. Szent Iván hava (June, 'Saint John [the Baptist]'s month')
7. Szent Jakab hava (July, 'Saint James' month')
8. Kisasszony hava (August, 'month of the Virgin')
9. Szent Mihály hava (September, 'Saint Michael's month')
10. Mindszent hava (October, 'all saints' month')
11. Szent András hava (November, 'Saint Andrew's month')
12. Karácsony hava (December, 'month of Yule/Christmas')

1. Leden – derives from 'led' (ice)
2. Únor – derives from 'nořit' (to dive, referring to the ice sinking into the water due to melting)
3. Březen – derives from 'bříza' (birch)
4. Duben – derives from 'dub' (oak)
5. Květen – derives from 'květ' (flower)
6. Červen – derives from 'červená' (red – for the color of apples and tomatoes)
7. Červenec – is the second 'červen' (formerly known as 2nd červen)
8. Srpen – derives from old Czech word 'sirpsti' (meaning to reflect, referring to the shine on the wheat)
9. Září – means 'to shine'
10. Říjen – derives from 'jelení říje', which refers to the estrous cycle of female elk
11. Listopad – falling leaves
12. Prosinec – derives from old Czech 'prosiněti', which means to shine through (refers to the sun light shining through the clouds)[12]

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".

1. Thout
2. Paopi
3. Hathor
4. Koiak
5. Tooba
6. Emshir
7. Paremhat
8. Paremoude
9. Pashons
10. Paoni
11. Epip
12. Mesori

The Nisga'a calendar coincides with the Gregorian calendar with each month referring to the type of harvesting that is done during the month.

1. K'aliiyee = Going North – referring to the Sun returning to its usual place in the sky
2. Buxwlaks = Needles Blowing About – February is usually a very windy month in the Nass River Valley
3. Xsaak = To Eat Oolichans – Oolichans are harvested during this month
4. Mmaal = Canoes – The river has defrosted, hence canoes are used once more
5. Yansa'alt = Leaves are Blooming – Warm weather has arrived and leaves on the trees begin to bloom
6. Miso'o = Sockeye – majority of Sockeye Salmon runs begin this month
7. Maa'y = Berries – berry picking season
8. Wii Hoon = Great Salmon – referring to the abundance of Salmon that are now running
9. Genuugwwikw = Trail of the Marmot – Marmots, Ermines and animals as such are hunted
10. Xlaaxw = To Eat Trout – trout are mostly eaten this time of year
11. Gwilatkw = To Blanket – The earth is "blanketed" with snow
12. Luut'aa = Sit In – the Sun "sits" in one spot for a period of time

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:

1. Vendémiaire
2. Brumaire
3. Frimaire

• Winter:

1. Nivôse
2. Pluviôse
3. Ventôse

• Spring:

1. Germinal
2. Floréal
3. Prairial

• Summer:

1. Messidor
2. Thermidor
3. Fructidor

Ojibwe month names are based on the key feature of the month. Consequently, months between various regions have different names based on the key feature of each month in their particular region. In the Eastern Ojibwe, this can be seen in when the sucker makes its run, which allows the Ojibwe to fish for them. Additionally, in the Eastern Ojibwa-Chippewa-Ottawa Dictionary, Dr. Richard Rhodes also informs of not only the variability in the month names but how in the Eastern Ojibwe, these names were originally applied to the lunar months the Ojibwe originally used, which was a lunisolar calendar marked by the moon, fixed to Akiinaaniwan (typically December 27) that marks when sunrise is the latest in the Northern Hemisphere. Due to Eastern Ojibwe is a vowel syncope dialect, the elided vowels (and the occasionally elided consonants) have been added back in the table below, shown in brackets.