Lunisolar Calendars track the rhythm of nature better

Lunisolar Calendars track the rhythm of nature better.

by tonytran2015 (Melbourne, Australia).

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(Blog No.123).

#lunisolar calendar, #lunar calendar, #solar term, #tiết, #leap month, #solstice, #moon phase,

When traveling to Asia, Westerners are often surprised that many locals still use Lunar Calendars. The mystery will dissolve when they know more about Lunar Calendars.

In terms of survival, East Asian Lunar Calendars offer many advantages which keep them in use in East Asia and maybe in some other countries as well.

1. The East Asian Lunisolar Calendars.

The East Asian Lunisolar Calendars are based on Lunar Months and on Seasons.

They have the following characteristics:

1. A new month begins with the appearance of a New Moon any time during the WHOLE night of of the first day of the new month.

Note that a Lunar “day and night” period in East Asian Lunar Calendar just mean exactly that. It does not means from midnight to the following midnight. A Lunar “day and night” starts on a Sunrise and end at the next Sunrise.


Figure 1: Phase of the Moon. A new Moon is the Moon with a thin white crescent on its leading edge (top right corner of the picture) which is first visible right after sunset on the Western horizon

2. The New Year of East Asian Lunar Calendar has been traditionally celebrated only from the First day (after Sunrise) of the New Year. The Midnight Firecracker Celebration on the last night of the expiring year is a hybrid concept of the beginning of a New Year.

The Firecracker custom by Chinese was traditionally used to keep some “Evil dragon” away from people’s houses during the change of guards in Heaven and at family Altars.

3. The post-solstice Month following a Winter Solstice (December 21st) is called the Final Month (“tháng Chạp” in Vietnamese meaning Preservation (?) Month).

4. The Month following the post-Solstice Month is ALWAYS a First Month of the next year (“tháng Chánh” in Chinese Vietnamese meaning Principal Month, “tháng Giêng” in Vietnamese).

5. Months are given names like Month 1 (First or Principal Month), Month 2, …, Month 11, Final Month (post-Solstice and last month).

6. As the beginnings of days and Lunar months depend on the longitude of an observer, the beginning of days, months may differ between countries seperated by few degrees in longitude. The Lunisolar Calendars of China, Korea, Taiwan and Vietnam may have their New Years differing by more than 28 days.

7. As Lunar months are only about 29.5 days long, every few (nearly 3) years there will be one Lunar year with 13 Lunar months. The additional month is called a Leap Month for that year.

8. As East Asian lives have been traditionally based on agriculture, the Lunar Calendars must help people track seasons. The Lunar months are named so that each denotes a particular time of the seasons.

For examples:

There is a folk phrase in Vietnamese “Tháng Năm (5) chưa nằm đã sáng, Tháng Mười (10) chưa cười đã tối.” It means 5th Months have shortest nights while 10th Months have shortest days.

One of planters’ songs about planting times for various crops in Vietnam is “Tháng chạp là tháng trồng khoai, Tháng giêng trồng đậu, tháng hai trồng cà. Tháng ba cày vỡ ruộng ra, Tháng tư làm mạ mưa sa đầy đồng. Ai ai cùng vợ cùng chồng, Chồng cày vợ cấy, trong lòng vui thay. Tháng năm gặt hái đã xong, Nhờ trời một mẫu năm nong thóc đầy…”. It means “final month is for planting root crops, principal month planting bean crops, second month tomato crops. Third month is for tilting and ploughing soil, fourth month for planting rice seedlings under the rain, …, fifth month comes with all harvesting well finished,…”

9. To preserve the characters of months, the leap month in any year with 13 Lunar months is inserted between month 1 and month 11 such that seasonal characters of other months are preserved.

10. There are 24 nearly equally spaced, designated (by East Asian Astronomers) marker points on the Ecliptic called “Solar terms” in “Chinese English”. The position of the Sun relative to these markers tell its progress along the Ecliptic and the season in the year. Any leap month is inserted such that the Sun does not go far from its expected positions for the month [6].

star map mercatorx1p6

Figure: The wavy line in this Mercator map of the sky is the Ecliptic. The Sun travels on it. There are 24 marker points on this line used by East Asian Astronomers to quantify the position of the Sun on this line.

The time the Sun goes past any marker is called a “tiết” in Old Chinese-Vietnamese; “tiết” means a beginning of any one of 24 sub-seasons in the exact solar year (Each traditional astronomically based season is further subdivided into six sub-seasons by East Asian Astronomers.). There are 24 sub-seasons of roughly equal lengths and their 24 “tiết”s with 24 individual names:

Solar R.A. = 270°冬至 dōngzhì Đông chí Dec 22 11th winter maximum (solstice). DATE for ANCHORING 11th month. This anchoring may make months 11 in neighbouring countries differ by nearly 28 days.

Solar R.A. = 285°小寒 xiǎohán Tiểu hàn Jan 6, bit frigid

Solar R.A. = 300°大寒 dàhán Đại hàn Jan 20 most frigid, roughly the middle of 12th month,

Solar R.A. = 315°立春 lìchūn Lập xuân Feb 4 spring begins, close to the beginning of CONVENTIONAL 1st month, There is NO LEAP month from 11th to 1st month.

Solar R.A. = 330°雨水 yǔshuǐ Vũ thủy Feb 19, more rain than snow, LEAP month may be inserted after 1st monrh and before 11th month.

Solar R.A. = 345°驚蟄 (惊蛰)jīngzhé Kinh trập啓蟄 Mar 6, hibernating insects awaken,

Solar R.A. = 0°春分 chūnfēn Xuân phân Mar 21 2nd month midpoint, spring center (equinox) , Target date for middle of 2nd month,

Solar R.A. = 15°清明 qīngmíng Thanh minh Apr 5, clear and bright

Solar R.A. = 30°穀雨 (谷雨) gǔyǔ Cốc vũ Apr 20 3rd month midpoint wheat rain , Target date for middle of 3rd month,

Solar R.A. = 45°立夏 lìxià Lập hạ May 6, summer begins

Solar R.A. = 60°小滿 xiǎomǎnTiểu mãn小満 May 21 creatures plentiful , Target date for middle of 4th month,

Solar R.A. = 75°芒種 (芒种) mángzhòng Mang chủng Jun 6, seeding millet

Solar R.A. = 90°夏至 xiàzhì Hạ chí Jun 21 summer maximum (solstice) , Target date for middle of 5th month,

Solar R.A. = 105°小暑 xiǎoshǔ Tiểu thử Jul 7, bit sweltering

Solar R.A. = 120°大暑 dàshǔ Đại thử Jul 23 most sweltering , Target date for middle of 6th month,

Solar R.A. = 135°立秋 lìqiū Lập thu Aug 8 autumn begins

Solar R.A. = 150°處暑 (处暑)chǔshǔ Xử thử Aug 23 heat withdraws , Target date for middle of 7th month,

Solar R.A. = 165°白露 báilù白露 Bạch lộ Sep 8 dew

Solar R.A. = 180°秋分 qiūfēn Thu phân Sep 23 autumn center (equinox) , Target date for middle of 8th month,

Solar R.A. = 195°寒露 hánlù Hàn lộ Oct 8 cold dew

Solar R.A. = 210°霜降 shuāngjiàng Sương giáng, Oct 23 frost , Target date for middle of 9th month,

Solar R.A. = 225°立冬 lìdōng Lập đông Nov 7 winter begins

Solar R.A. = 240°小雪 xiǎoxuě Tiểu tuyết Nov 22 snows a bit , Target date for middle of 10th month,

Solar R.A. = 255°大雪 dàxuě Đại tuyết Dec 7 snows a lot

The leap month is inserted so that months with the same names mostly contain the same solar-determined sub-seasons over years.

2. Disadvantages of Lunisolar Calendars.

1. The lengths of months do not follow any simple pattern.

2. Calendar users have to rely on central astronomers to know when is a leap year and which month will be the leap month for that leap year.

3. As the beginnings of days and Lunar months depend on the longitude of an observer, the beginning of days, months may differ between countries separated by few degrees in longitude. The Lunisolar Calendars of China, Korea, Taiwan and Vietnam may have their New Years differing by more than 28 days.

4. The number of days between any two given dates are hard to calculate.

5. Consequently it is difficult for house builders or any contractors to work out the number of working days in any project. However, East Asians are often concerned with weekly matters (how long is the harvest period, etc..,) or with decade long matters (when and where will their children live, migrate to!).

3. Advantages of Lunisolar Calendars.

1. The day in the calendar month is displayed by the Moon. Some Vietnamese can tell the day without any delay just by looking at the Moon.

2. Market days and Buddhist fasting and festival days are always on the 15th day of the Lunar months. There is plenty of Moonlight on those days.

3. The tides are strongest on full Moon and No-Moon days. This makes easy planning with water transportation on rivers and canals. (Wedding celebrations in remote areas in Southern Vietnam are still carried out with great timing precision so that guests can arrive and return by boats).

4. Any two distant parties may agree to conveniently meet each other halfway at each full-Moon.

5. Before full Moon, the lit side of a Non-full Moon always points Westwards. After full Moon, it points Eastwards. So the Calendars help with nighttime navigating.

6. Rodents and insects are exposed to their predators (such as night-owls, cats, snakes…) at night in full Moon. So their nighttime forage depends on Moon phase and days in the Lunar months.

7. Seeds and succulent seedlings are exposed to rodents and insects in Moon lit nights. Planters (including Asian and European) have known it is best to count days from full Moon to plant various seeds.

8. Water creatures like crabs do get fattened or skinny depending on Moon phase (probably due to their feeding and mating habits). Vietnamese wisdom advises against buying crabs for meals after full Moon.

4. Conclusion.

Lunisolar calendars track the rhythm of nature better. People in East Asia may retain the calendars as their lives are more dependent on this rhythm.




[3]. Sima Qian, Records of History by the grand historian (translated by Burton Watson), Qin Dynasty, Han Dynasty I (Rev. Ed.) and Han Dynasty II (Rev. Ed.), the Res. Cent. for Transl. The Chinese Univ. of Hon Kong and Colubia Univ. Press, Hong Kong and New York, 1961. Han Dynasty II p.38 showed that in 113BC, month 11 has the solstice.

[4]. Helmer Aslaksen, The Mathematics of the Chinese Calendar,, accessed 19 Jan 2017.

[5]. Ho Ngoc Duc, Thuat toan am lich (in Vietnamese),, accessed 19 Jan 2017.



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