This year there shall be two Jyeshthas. We call them first and second Jyeshtha. There are four Pakshas in two months. First Jyeshtha commences from Krishna Paksha. It is followed by Shukla Paksha of 1st Jyeshtha, then Krishna Paksha of 2nd Jyeshtha and finally Shukla Paksha of 2nd Jyeshtha. The Krishna Paksha of 1st Jyeshtha and Shukla Paksha of 2nd Jyeshtha is considered true or pure Jyeshtha month. The remaining two Pakshas i.e. Shukla Paksha of 1st Jyeshtha and Krishna Paksha of 2nd Jyeshtha comprise to make extra month which is known as Adhik Masa or Mal Masa. No auspicious ceremony except meditation or spiritual activity is performed during this Adhik Masa.
This type of system is available in Luni-Solar calendar of Northern India only. Gujarati calendar is also based on Luni-Solar motion but in this calendar month begins from Shukla Paksha. Therefore in Gujarati calendar the first month itself is extra or Adhik or Mal Masa and 2nd month is considered pure or shuddh month. Muslim calendars are also based on lunar motion but in this calendar there is no extra month(Adhik Masa) and for this reason this calendar moves faster slowly. If the month of Ramjaan was falling in August in 2006 then it shall fall in July in 2007 now. This type of shifting of month or extra month is not there in Luni-Solar or Solar calendars.
Let us make an analysis of the basis of calculation of Adhik Masa.
The earth is revolving around the Sun. This earth completes one circle around the Sun in 365.2564 days(365 days 6 hours 9 minutes & 12.96 seconds) whereas Moon takes 29.5306 (29 days 12 hours 44 minutes & 3.84 seconds ) days from new moon (Amavasya) to next new moon. According to this number of days in a month are 29.5306. Number of days in 12 months = 29.5306x12=354.3672 days.
The difference between one year of earth & 12 months of Moon is 10.8992 days = 11 days.
Therefore every year lunar months comes 11days earlier but in 3 years this difference reaches upto 33 days, which is more than one month. We call this as Adhik Masa.
Generally Adhik Masa comes after an interval of 2 years and 4 months, 2 years and 9 months, 2 years and 10 months or 2 years and 11 months. On an average Adhik Maas comes in 2 years and 8.5 months. This value can be verfied dividing the duration of month i.e. 29.5 days by 10.9. Lunar year is 10.9 days smaller than solar year therefore after dividing 29.53/10.9=2 years and 8.5 months there arises a difference of one month.
See the occurence of Adhik Masa in last few years
Generally new moon (Amavas) falls once between two Sankrantees that is Sun's transit into next sign. Minimum value of two Sankrantees is 29 days 10 hours and 48 minutes and maximum value is 31 days 10 hours and 48 minutes whereas the minimum value of two newmoons 29 days 5 hours 54 minutes and 14 seconds and the maximum value of two new moons 29 days 19 hours 36 minutes and 29 seconds. Therefore, it happens very rarely that no new moon falls between two Sankrantees. This generally happens after 19 years, or after 141 years, and sometimes after 65, 76 or 122 years. This type of situation is termed as Kshaya Masa. This is possible during small signs like Scorpio, Sagittarius and Capricorn only. This implies Kshaya Masa can happen during Aghan, Paush and Magha only because in all other months the duration of Sankranti of Sun is more than lunar month.
Whenever Kshay Masa is there certainly there shall be two Adhik Masas one before and one after Kshay Masa. Following Kshay Masas happened in last over one thousand years :-