Names of Lunar Months

The twelve lunar months of Indian Lunar calendar have names which are derived from names of twelve out of twenty-seven Nakshatra names. It is clear that the Nakshatra were given their names first. How twelve out of those have been selected for deciding month names? When did the nakshatras get their names and when the months got their names? The ancient texts of vedas etc. may have indications of these events.

Lunar months are only about 29 ½ days and 12 lunar months amount to only 354 days, short of the solar year of 365+ days. In order to keep step with Solar year, some nameless, ‘adhika’,lunar months need to be introduced. Jews follow a lunar calendar and have a system of such extra months in a 19 year cycle. The Muslims also follow lunar months but they do not have any extra months. Their year is just 12 lunar months. They are quite aware that their year is shorter than the Solar year but have lived with it all these years.

Solar year is also slightly larger than 365 days. A correction unit being ‘a day’, the system of leap years enables a much easier adjustment. Only a small change in the rule of Leap year of Julian calendar made the Gregorian Calendar more accurate. With lunar months and solar year, adjustment to catch-up is not easy, the unit being a full month!

The current system of naming Lunar months is not very old. It is linked with Sun’s motion through the ecliptic. Our ancestors had divided the ecliptic into 27 parts to match the approx. 27 days moon takes to pass through the ecliptic. The system of dividing the ecliptic into 12 equal parts called Rashis is linked with the approx 12 lunar months Sun takes to pass through the ecliptic. I believe, The Rashi System came to India from the Greeks. The Indian names of rashis are derived from the Greek names.

The current system of naming the Lunar month is based on Sun’s crossing over from one rashi to the next within the month. If Sun does not cross over within a Lunar month, then no name can be given to it and it becomes an Adhika month, but with the name same as the next regular month. Very rarely, Sun crosses over two Rashis in a lunar month and one month name needs to be skipped. We then get a Kshaya masa. When exactly, this system came into vogue? I have not come across any specific date or year when it started and who started it. The answer should be there somewhere but I dont know it.

Before that, what was the system of naming months and taking Adhika Masa? It is known that after approx 29 normal months an Adhika Masa needs to be taken to catch up with the seasons (Ritus). But it is not exact! So what were the rules?

Our ancestors may have started with no Specific Adhika Masa System as such. Exact and correct systems develop progressively over long time. So initially, only as and when the mismatch between the month name and Ritu became obvious, some adhika masas may have been taken at random. Then it may have been noticed that after 58 continuous normal months, the mismatch equals a full Ritu of two months. So, take two nameless months and fall in step. This was the system prevailing at Mahabharata Time. In the whole of Mahabharata the only reference to Adhika masa is in what Bhishma said at the time Arjun came out of Adnyatavasa and appeared before the Kouravas for battle. He was recognized. When the question arose whether 12+1 =13 years were over, Bhishma explained that after every 58 normal months, two Adhika Masas need to be taken. (पंचमे पंचमे वर्षे मासद्वयम् is the wording). Since there is no other system mentioned anywhere, we have to accept that this was the system then prevailing. Since when it was in use? Not known.