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

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

Approximatelyevery third year, an extra month is included between the third andfourth months. This is to reconcile the lunar calendar with the solarone.

Unlikeour centuries of 100 years, the Vietnamese calendar is divided into60-year periods called "Hoi". This "Hoi" or 60-year period is dividedinto two shorter cycles; one of a ten-year cycle and the other of a12-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

     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

AVietnamese year is named after the combination of one of the names ofthe 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 thefirst of the ten-year cycles and Thin is the fifth of the 12-yearcycle. 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.

TheVietnamese like the lunar calendar because they can be sure of a fullmoon on the 15th day of each month. The lunar calendar can be quiteprecise and synchronized with the seasons so long as correctastronomical data are used.