Vietnamese Lunar Calendar

Though today, people in Vietnam use the western calendar for most practical matters of daily life, the old system still serves as the basis for determining numerous seasonal holidays. This coexistence of two calendar systems has long been accepted by Vietnamese people. As with the Chinese, Vietnamese lunar calendar begins with the year 2637 B.C. It has 12 months of 29 or 30 days each, and the year totals 355 days.

A lunar month is determined by the period required for the moon to complete its full phasic cycle of 29 and a half days, a standard that makes the lunar year a full 11 days shorter than its solar counterpart. This difference is made up every 19 years by the addition of seven lunar months. The 12 lunar months are further divided into 24 solar divisions distinguished by the four seasons and times of heat and cold, all bearing close relationship to the yearly cycle of agricultural work.

Approximately every third year, an extra month is included between the third and fourth months. This is to reconcile the lunar calendar with the solar one.

Unlike our centuries of 100 years, the Vietnamese calendar is divided into 60-year periods called “Hoi”. This “Hoi” or 60-year period is divided into two shorter cycles; one of a ten-year cycle and the other of a 12-year cycle.

The ten-cycle, called “Can” is composed of ten heavenly stems. Their names and approximate translation are as follows:

1. Giap     water in nature
2. At         water in the home
3. Binh     lighted fire
4. Dinh     latent fire
5. Mau      wood of all types
6. Ky        wood set to burn
7. Canh    metal of all kinds
8. Tan      wrought metal
9. Nham   virgin land
10. Quy      cultivated land

The 12-year cycle, “Ky”, has 12 earthy stems represented by the names os 12 names in the zodiac. Their names and translations in order are:

1. Ty       the rat
2. Suu    the buffalo
3. Dan    the tiger
4. Mao    the cat
5. Thin    the dragon
6. Ty       the snake
7. Ngo    the horse
8. Mui     the goat
9. Than   the monkey
10. Dau     the cock (the chicken)
11. Tuat    the dog
12. Hoi      the pig

A Vietnamese year is named after the combination of one of the names of the ten heavenly stems and one of the names of the 12 earthly stems. For instance, 1964 was the Year of the Dragon, “Giap-Thin”. Giap is the first of the ten-year cycles and Thin is the fifth of the 12-year cycle. The year 1965 was “At-Ty”. This follows down the line each year. The ten-year stem is not usually mentioned when discussing the year. Thus, we hear “the Year of Dragon” or “the Year of Snake”, etc. Giap-Thin, the Year of Dragon, will not return for a 60-year period. This is true of all combinations.

The Vietnamese like the lunar calendar because they can be sure of a full moon on the 15th day of each month. The lunar calendar can be quite precise and synchronized with the seasons so long as correct astronomical data are used.