Māsa: Lunar, Solar, and Luni-Solar Months
Why the same festival can fall in two different 'months', and the three kinds of month behind it
Ask two Indians which month a festival falls in and you may get two different answers, both correct. Learn why: the north ends its months at the full moon and the south at the new moon, and behind both lie three distinct kinds of month, lunar, solar, and sidereal, each measuring a different real motion of the sky.
The Same Festival, Two Different Months
Ask a friend in Varanasi and a friend in Hyderabad which month a certain festival falls in, and you may hear two different month-names for the very same day, and both will be right. It is one of the small puzzles of the Indian calendar. A festival that a north Indian places in the month of Śrāvaṇa, a south Indian may place in the preceding month. Nobody has made a mistake. The two regions simply cut their months at different points, and to understand why, we have to look at what a māsa, a month, actually is, and discover that there is more than one kind.
The month sits at the heart of the Indian calendar, larger than the tithi and the week, and it is where the tradition's luni-solar cleverness is fully on display. This lesson lays out the three kinds of month, the regional split that names them differently, and how the tradition kept the Moon's month wedded to the Sun's year.
Three Ways to Measure a Month
A "month" is roughly the Moon's cycle, but the Moon runs more than one kind of cycle, and each gives a different month.
- The synodic month, from one new moon to the next, is the cycle of the phases, about 29.5 days. This is the everyday lunar month, and Āryabhaṭa defines it precisely as the interval between conjunctions of the Sun and Moon.
- The sidereal month, the time for the Moon to return to the same star, is shorter, about 27.3 days, because while the Moon circles, the Sun has moved on, so the Moon must travel a little further each cycle to catch the Sun again.
- The solar month is different in kind: it is the time the Sun spends in one sign of the zodiac, one rāśi, about 30.4 days. Twelve solar months make the solar year exactly.