At 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.
The Vietnamese like the lunar calendar because they can be sure of a full moon on the 15th day of each month. in their everyday life, however, they use the Gregorian calendar.
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 follow.
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 the Dragon" or the "Year of the Snake", etc., etc., Giap-Thin, the Year of the Dragon, will not return for a 60-year period. This is true of all combinations.
