the following passage is an expansion of what I have written to a
friend and member of the group.
When is Vesak?
The exact date of Vesak can be confusing. The confusion is the result
of the many different calendars used across the world. In the past,
astronomers studied the movement of celestial objects in the sky, and
observed a pattern in it. The pattern, as they have recorded, slowly
evolved into a calendar. Becuase these studies were conducted more or
less independently, hence we have the various calendars in used today.
According to the Tipitaka, Buddha was born, enlightened and obtained
final nibbana on the full-moon day of Vesakha. Hence, we call this day
Vesak Day. The word vesak comes from vesakha, which is derived from
Sanskrit vaishakha, the second month on the Hindu calendar. The Hindu
new year commences on the new-moon day of the month of Chaitra, which
falls between March and April on the Gregorian calendar. Other names
for Vesak Day include Wesak Day, Visakah Puja, Visakah Bucha, Buddha
Purnima (meaning 'full-moon'), Buddha Jayanti (meaning 'victory'), and
Buddha Day.
Conventionally, we take Vesak Day as the full-moon day in the month of
May. However, the lunar month (29/30 days) is always shorter than the
calendar month (30/31 days, except February). Therefore, every few
years, we will find two full-moon days in May. This year (2007), we
have full-moon days on May 1 and 31.
The World Buddhist Federation passed a resolution in 1950 that for
such cases, the first full-moon day in May will be Vesak Day. Based on
this, Malaysia and Sri Lanka set May 1 as Vesak Day. However, it is
argued, as in for 2007, that, traditionally, Vesak Day is considered
the full-moon day of the fourth lunar month on the Chinese calendar.
And according to the Chinese calendar in 2007, May 31 is the full-moon
day of the fourth lunar month. Based on this, Singapore set May 31 as
Vesak Day.
There are generally three types of calendar: solar, lunar and lunisolar.
The solar calendar is based on the revolution of the earth around the
sun, with no consideration of moon phases. Each revolution is one
complete seasonal cycle. However, we also measure time in terms of
days. And, unfortunately, the earth's complete revolution around the
sun takes slightly over 365 days. Therefore, we have to introduce an
extra day every four years in the month of February. The Gregorian
calendar used internationally is a solar calendar.
A lunar calendar is a 12-month calendar based on the cyclic movement
of the moon, with no consideration of the solar cycle. The moon takes
29.5 days to revolve around the earth. So, there are 354 days in a
year. A holiday celebrated based on a lunar calendar will fall 11 days
earlier each solar year. The Islamic calendar is a lunar calendar.
The Chinese calendar is a lunisolar calendar, i.e. for every two to
three years, an extra (intercalary) month is introduced to correct for
its deviation from the astronomical year. The Chinese calendar is
traditionally a lunisolar calendar, it is not an influence of modern
astronomy. As such the calculation of the intercalary month requires
complex astronomical knowledge, and based on this complex calculation,
the intercalary month may be placed anytime in a leap year. Hence,
there can be two fourth lunar months with full-moon days in a leap
year! When that happens, Vesak will be celebrated on the first of the
two fourth lunar months.
Another point to note is that by following the Chinese calendar, Vesak
may fall outside May. For example, Vesak Day was celebrated on June 2
in 2004.
In Thailand, Vesak Day falls on the full-moon day of the sixth lunar
month. If there are 13 full moons in a year, Vesak Day falls on the
full-moon day of the seventh lunar month.
Vesak as the "triple-occasion" of Buddha's birth, enlightenment and
parinibbana is traditionally observed only in southern-transmission or
Theravada countries. The northern-transmission or Mahayana countries
traditionally celebrate the three occasions on three separate days.
For example, the Chinese marked the eighth day of the fourth lunar
month as the day of Buddha's birthday. Buddha's enlightenment and
parinibbana were marked on the eigth day of the twelfth month and the
fifteenth (full-moon) day of the fourth month respectively, in the
Chinese calendar.