Archived posting to the Leica Users Group, 2004/01/22

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Subject: RE: [Leica] Happy New Year !
From: "Phong" <>
Date: Thu, 22 Jan 2004 14:56:03 -0500

Joseph Low wrote:
> Phong - no coincidence - historically the Vietnamese adopted the Chinese
> Lunar Calendar - therefore CNY & Tet will always be simultaneous :)

Hi Joseph,

What you say is common belief, even among many Vietnamese, though
I beg to differ; while the two countries use the same rules*
to compute the calendars, there two reasons the calendars sometimes

1. The Vietnamese use meridian 105 East (Hanoi) and the Chinese
use meridian 120 East (Beijing) for the calculations,
thereby there are times when the calendars differ.  A simple example is
the case when the moment of the first new moon occur between
11:00 and 12:00PM Hanoi time; in that case the New Year would
occur one day later in the Chinese calendar than the Vietnamese
one.  In rare cases, the New Years may be a (lunar) month apart.

2. Even when using the same rules, errors were not infrequent,
resulting in different calendars in the past.  I don't expect
we see this much in modern times.

It is true that historically, there were times when Vietnam adopted
the official Chinese imperial calendar.  And it is also true that
in the vast majoity of the cases, the New Years coincide.  But the
Vietnamese, with their fierce spirit of independence, insist on the
difference.   :-)

By the way, chinese calendrical calculations and astronomy is a topic of
interest to me.  See for example the stuff covered by the late Joseph
Needham's "Science and Civilisation in China, Volume III, Mathematics and
the Sciences of the Heavens and Earth".

Haapy New Year !

- - Phong

* Here are the rules:
1. All calculations and observations are based on the meridian 120 degree
   (115 degree East for Vietnam)
2. The day starts at midnight  (it used to start at the beginning of the
   first hour, the hour of the rat, which starts at 11:00pm)
3. The day on which occur the new moon is the first day of the month
4. The winter solstice (dong zhi jie qi) must fall in the 11th month of the
5. If there are 13 lunar months between 2 winter solstices, one of them must
   necessarily not have a zhongqi**;  that month is the leap month in the
   corresponding year (hence a leap year has 13 lunar months).

** The solar year is divided into 24 jieqi, each corresponding to positions
of the Earth along its orbit, each 15 degree apart.  The length of each
varies from 14 to 16 days, varying with the speed of Earth along its orbit.
Every other jieqi is a zhongqi; the winter solstice is a zhongqi.

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