Chinese Leap Lunar Months |
First, we need to know the difference between the Chinese Astronomical Calendar and the Civil Calendar. The Chinese Civil Calendar is posted by the Chinese government. The Chinese Astronomical Calendar is used by astronomers who work for government. The Astronomical Calendar is much more accurate than the Civil Calendar. The major difference is the assignment of Leap Months (Intercalary Months). We know a leap month is assigned if a lunar month (new moon to new moon) has no Solar Center Point. But, what do we do when the new moon day and the Solar Center Point fall on the same day?
If the new moon day and the Solar Center Point are on the same day, the lunar month contains that Solar Center Point in the Civil Calendar system. In the Astronomical Calendar, we have to compare the new moon time and the Solar Center Point time (hour, minute and second). The lunar month contains that Solar Center Point only if the Solar Center Point time comes after new moon time.
Because they are different, the listing of leap month assignments is different. From the following comparison charts of Beijing Time, PST and EST from 1979-2001. We find
China Beijing Time or Taiwan Standard Time - Longitude East 120th degree |
China Civil Calendar | China Astronomical Calendar |
Year | New moon | Leap month | Year | New moon | Leap month |
---|---|---|---|---|---|
1979 | 07-24 09:41 | 06 | 1979 | 07-24 09:41 | 06 |
1982 | 05-23 12:40 | 04 | 1982 | 05-23 12:40 | 04 |
1984 | 11-23 06:57 | 10 | N/A | ||
1985 | 02-20 02:43 | 01 (Removed) | 1985 | 04-20 13:22 | 03 |
1987 | 07-26 04:37 | 06 | 1987 | 08-24 19:59 | 07 |
1990 | 06-23 02:55 | 05 | 1990 | 06-23 02:55 | 05 |
1993 | 04-22 07:49 | 03 | 1993 | 05-21 22:06 | 04 |
1995 | 09-25 00:55 | 08 | 1995 | 10-24 12:36 | 09 |
1998 | 06-24 11:50 | 05 | 1998 | 07-23 21:44 | 06 |
2001 | 05-21 10:46 | 04 | 2001 | 06-21 19:58 | 05 |
Pacific Standard Time (PST) - USA Longitude West 120th degree |
Civil Calendar | Astronomical Calendar |
Year | New moon | Leap month | Year | New moon | Leap month |
---|---|---|---|---|---|
1979 | 06-24 03:58 | 05 | 1979 | 07-23 17:41 | 06 |
1982 | 05-22 20:40 | 04 | 1982 | 05-22 20:40 | 04 |
N/A | N/A | ||||
1985 | 03-21 03:59 | 02 | 1985 | 04-19 21:22 | 03 |
1987 | 08-24 03:59 | 07 | 1987 | 08-24 03:59 | 07 |
1990 | 06-22 10:55 | 05 | 1990 | 06-22 10:55 | 05 |
1993 | 05-21 06:06 | 04 | 1993 | 05-21 06:06 | 04 |
1995 | 09-24 08:55 | 08 | 1995 | 10-23 20:36 | 09 |
1998 | 07-23 05:44 | 06 | 1998 | 07-23 05:44 | 06 |
2001 | 06-21 03:58 | 05 | 2001 | 06-21 03:58 | 05 |
Eastern Standard Time (EST) - USA Longitude West 75th degree |
Civil Calendar | Astronomical Calendar |
Year | New moon | Leap month | Year | New moon | Leap month |
---|---|---|---|---|---|
1979 | 06-24 06:58 | 05 | 1979 | 07-23 20:41 | 06 |
1982 | 05-22 23:40 | 04 | 1982 | 05-22 23:40 | 04 |
N/A | N/A | ||||
1985 | 04-20 00:22 | 03 | 1985 | 04-20 00:22 | 03 |
1987 | 08-24 06:59 | 07 | 1987 | 08-24 06:59 | 07 |
1990 | 06-22 13:55 | 05 | 1990 | 06-22 13:55 | 05 |
1993 | 05-21 09:06 | 04 | 1993 | 05-21 09:06 | 04 |
1995 | 09-24 11:55 | 08 | 1995 | 10-23 23:36 | 09 |
1998 | 07-23 08:44 | 06 | 1998 | 07-23 08:44 06 | 06 |
2001 | 05-22 21:46 | 04 | 2001 | 06-21 06:58 | 05 |
Issues of Leap Months
The Chinese Lunar Calendar system would be perfect, if the length of solar month was always longer than the length of a lunar month. If a lunar month is longer than a solar month, then it's possible that a lunar month contains two solar Center Points. We can call such month as the Double-Center-Point Lunar Month. For example, the lunar month in the December of 2052 contains Winter Solstice 2052/12/21 04:18:32 and Severe Cold 2053/01/19 15:00:35 in the following table of Chinese Astronomical Calendar.
Solar or Lunar Date and Time | Center Point or New Moon Time |
2052/11/21 14:47:21 | C |
2052/12/21 04:16:00 | N |
2052/12/21 04:18:32 |
C |
2053/01/19 15:00:35 | C |
2053/01/19 23:13:00 | N |
2053/02/18 05:03:15 | C |
2053/02/18 16:32:00 | N |
2053/03/20 03:48:44 | C |
2053/03/20 07:12:00 | N |
2053/04/18 18:49:00 | N |
2053/04/19 14:31:37 | C |
2053/05/18 03:44:00 | N |
2053/05/20 13:20:55 | C |
When a lunar month contains two solar Center Points, then there will be a month nearby without any Center Point. Such a month without any Center Point is not a Leap Month, is called a Fake Leap Month. Therefore, the lunar month 2053/03/20 07:12:00 in the March of 2053 is not a Leap Month.
Because this imperfection of Chinese Leap Month assignment, we need the 5th rule into the Chinese Calendar original rules.
All these five rules are good enough to make a nearly perfect Chinese Calendar. However, some articles about Chinese Calendar provides more rules. such as
There are no strong astronomical reasons to make those rules for Chinese Calendar. Actually, they are only thumb-of-rule to determine the location of Leap Months. When studying the Sun and Moon astronomical data, we can understand more about the issues on the assignments of Leap Month. Also, we will know more about the difference between Astronomical Calendar and Civil Calendar.
Sun and Moon Astronomical Data For Chinese Calendar