# Vietnamese lunar calendar

HELP NEEDED: I would like to have a look at the following article: Hoang Xuan Han, "Lich va Lich VN" , Tap-san Khoa-hoc Xa-Hoi, #9, thang 2, 1982 (Paris). Reprinted in: La Son Yen Ho Hoang Xuan Han, NXB Giao Duc, Ha Noi, 1998. Does anyone know where I can get a copy?

The following applet displays a month of the Gregorian calendar (du+o+ng li.ch) with the corresponding dates of the Vietnamese lunar calendar (a^m li.ch). The calculations are carried out with the algorithms described in the book Calendrical Calculations by Edward M. Reingold and Nachum Dershowitz, adapted for Hanoi time (GMT+7). They are explained briefly here.

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When the applet is loaded it shows the current month. The current day is displayed on a different background color. The lunar day is printed in red in the lower right corner of the cell and its name is printed below the table. You can click on any other day to show its name. Lunar leap months (tha'ng nhua^.n) are marked with an 'N', e.g., 12/2 N. To display another month please select the month and the year and press the "Display" button. The years BC must be entered as negative number, e.g., 2000 BC as -2000. You can move to the previous or next month using the buttons labelled "<<" and ">>".

If you wonder how the Vietnamese lunar calendar can be calculated for a date far in the future or back in the past, or why Vietnamese New Year and Chinese New Year sometimes fall on different days, you can find some explanations here. You will find there also some links to more calendar resources and source code for doing the required calculations.

# Lunar calendar calculations

The following applet calculates certain data for the Vietnamese lunar calendar (a^m li.ch). The following functions are supported:

• Show New Year's: calculates the New Year's days (Te^'t) for 100 years starting with the given year.
• Show Leap Months: calculates all leap months (tha'ng nhua^.n) for 100 years starting with the given year. (This takes some time.)
• Show Solar Terms: calculates the Solar Terms (tie^'t khi') for the given year
• Show New Moons: calculates the New Moons for the given year
Just select a function, enter the year and press "Compute".

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The New Year's days and the leap months depend on the time zone. Normally, Hanoi time (GMT + 420 min) is used for calculation. To compute these data for another time zone, change the number 420 in the right text field (after the "Clear" button) to another value, e.g., 480 for the time zone GMT+8. This is useful if you want to compute Chinese New Year's or data for the old Vietnamese calendar which was based on the GMT+8 time zone for some periods.

The names of the Solar Terms in Vietnamese:

Tie^?u Ha`n, DDa.i Ha`n, La^.p xua^n, Vu~ thu?y, Kinh tra^.p, Xua^n pha^n, Thanh minh, Co^'c vu~, La^.p ha., Tie^?u ma~n, Mang chu?ng, Ha. chi', Tie^?u thu+?, Dda.i thu+?, La^.p thu, Xu+? thu+?, Ba.ch lo^., Thu pha^n, Ha`n lo^., Su+o+ng gia'ng, La^.p ddo^ng, Tie^?u tuye^'t, Dda.i tuye^'t, Ddo^ng chi'
You can download the program to use offline. Please send your comments, suggestions, corrections to the author:
Ho Ngoc Duc <duc@informatik.uni-leipzig.de>