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Assumptions
and uncertainties related to the prediction of holidays based on the lunisolar
calendars
This page
provides additional information needed to better understand how Lunisolar
holidays dates were predicted in our database of
national public, bank and legal holidays. When looking at the dates of lunisolar
holidays for various countries (mostly in South-East Asia), it is important to bear in
mind the following points :
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Most rules used have been determined
empirically by fitting lunisolar rules to the data available from previous
years, and as many of the coming years currently available. While this may seem
a leap of faith considering the multitude of calendars in use in South-East
Asia, in fact it is a rather reasonable method (to determine holidays, at
least), as most of these calendars' holidays celebrate holidays either on the
New Moon or the Full Moon of a given lunar cycle that follows a specified solar
event (for example, the Full Moon of the 5th lunar cycle that began after the
Sun entered Aries).
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The latitude, longitude and timezone used
is usually that of the country's capital.
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The day is defined as beginning at
sunrise, except for some of the ethnic minority holidays in
Myanmar.
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Countries
that use holidays based on the Moon and/or Sun may decide to change the observed
date of these holidays either because of their occurrence on a week-end (Japan),
or because they occur on days that are deemed to be inauspicious (South-East
Asia). This adds an element of uncertainty of +/-2 days, although in
practice most dates we generate agree fully, and a few are only a day off.
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Finally, note that many countries in
South-East Asia are progressively changing the recurrence rule of some of their
lunar/solar holidays to rules based on fixed dates of the Western (Gregorian)
calendar. Therefore, while the lunisolar holidays' dates predicted for 2008 and
beyond are currently technically correct, the rules of these holidays may change
drastically in the next few years.
Bearing in mind the above points, the
dates for the lunar and/or solar events used are accurate to within minutes of
similar calculations, such as those of the
US Naval Observatory and the
Jet Propulsion Laboratory. If you have questions or comments, please
do not hesitate to contact us.
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