The calendar “date” that we are so familiar with
in our daily life is based on the solar calendar. The English calendar is a solar
calendar. The basis for the solar calendar is the rotation of the earth
around the Sun. It takes the earth approximately 365 ¼ days to
complete its rotation around the Sun. The English calendar that most of
us use today divides the 365 days of earth’s period of rotation around
the Sun in twelve months. The leap year, which occurs once every
four years, accounts for ¼ day per year.
Similar to the solar calendar a lunar calendar is
also popular and widely used in the Asian countries such as China, Pacific-rim
countries, Middle East countries, and India. The lunar calendar, which
is believed to have originated in India, has been around for a very long
time, even long before the solar calendar.
The lunar calendar is based on the moon’s rotation
around the earth. The lunar month corresponds to the one complete rotation
of the moon around the earth. Since this period of rotation of the moon around
the earth varies, the duration of the lunar month also varies. On average,
the lunar month has about 29 ½ days. In addition to the moon’s
rotation around the earth, the lunar year is based on the earth’s rotation
around the Sun. In general, the lunar year has twelve lunar months
of approximately 354 days, thus making it shorter by about 11 days than
the solar year. However, the lunar calendar accounts for this difference
by adding an extra lunar month about once every 2½ years.
This extra lunar month is known as the “Adhik Maas” in India (Adhik means
extra and the Maas means month). The concept of placing of the extra
month (meaning why and when should it be inserted between certain lunar months)
is as follow.
According to sidereal zodiac system the Sun
enters the first zodiac sign Aries (Mesh) on about April 15 of every year.
And about 15th of every month the Sun enters the next sidereal zodiac sign.
For example, as we know, every year on the day of Makar Sankranti the Sun enters the
sidereal zodiac sign Capricorn on about January 14. While Sun remains
in a zodiac sign for approximately one month, the Moon travels through
all twelve zodiac signs in about 27 ½ days. As a result, on
average, once about every two and half years, the entry of the Moon in
the same zodiac sign occurs twice while the Sun remains in the same sign.
In other words, when the Sun is traveling through the same zodiac sign,
the month during which two new moons occur, happens once about every 2
½ years. The lunar month corresponding to the period between
these two new moons is treated as the extra month or the Adhik Maas. Thus,
if the Adhik Maas occurs at the beginning of the lunar month Chaitra, then
it’s called as Adhik Chaitra, and the following lunar month would be then
the regular or Neej lunar month Chaitra.
The concept of the Adhik Maas (the extra month)
is similar to the “Blue Moon” in the West, which occurs almost with the
same frequency of 2 ½ years. The blue moon is the second full moon when
two full moons occur in the same month. Naturally the blue moon must
occur towards the end of month (some where between 29th,30th,or 31st of
Recall that the entry of the Sun in a sidereal zodiac
sign occurs around the middle of the calendar (solar) month (near 15th
of a month), thus, the Sun stays in a sidereal zodiac sign from about 15th
of a month to about 15th of the next month. Since for the Adhik Maas to
occur, two new moons must occur during when the Sun remains in the same zodiac
sign. Consequently, those new moons must occur near the15th of the successive
months. As a result, around the month of the Adhik Maas, the successive
full moons very likely occur about two weeks prior and during the
Adhik Maas or during and two weeks after the Adhik Maas . Indeed, the occurrence of the blue moon usually
takes place either during or two weeks after the
Adhik Maas .