Adhik Maas is an extra month in the Hindu calendar that is inserted to keep the lunar and solar calendars aligned. This month is dedicated to lord Vishnu, so it is also called as "Purushottam Maas".
Adhik Maas occurs in about every 32.5 months. In 2018, Adhik Jyaistha will be from 16 May to 13 June.
Calculations and Scientific significance of Adhik Maas
The solar year is made up of 365 days and about 6 hours, and the lunar year is made up of 354 days. There is a gap of 11 days, 1 hour, 31 minutes and 12 seconds between the lunar and the solar years.
According to Vasishtha Siddhanta, Purushottam Maas or the extra lunar month occurs after every 32 months, 16 days and 8 ghati. A ghati is 1/60th of a sidereal day, approximately 24 minutes, so 8 ghati is about 3 hours. It is one of the most accurate methods to adjust the gap between Solar and Lunar Year.
When the Sun does not transit into a new rashi (30° sidereal zodiac) but stays within a rashi in a lunar month (i.e. before a new moon), then that lunar month will be named according to the first upcoming transit. The transition of the sun from one rashi to the next is called Sankranti so a lunar moth without a Sankranti becomes adhik maas and named after next month with a Sankranti. The next month is called with its usual name.
No Adhik Maas falls during Margsheersh to Magh. A case of Adhik Karttik is extremely rare, but in the 250-year span (1901-2150 AD) it would occur once, in 1963.
Religious significance of Adhik Maas
During Purushottam Maas, people perform various types of religious rituals such as keeping fast recitation of religious texts, mantras, prayers, performing puja. Any graha dosh or specific dosh nivaran puja performed in Purushottam Maas to rectify the horoscope gives a ten times better result to the individual.
Marriages, mundan, inaugurations of new home (bhumi poojan, griha pravesh), fasting with desire of some worldy gains, buying new ornaments and vehicles are prohibited in this month.
The month of Purushottama has two ekadashis, Parama Ekadashi and Padmini Ekadashi. As per Skand Purana, the Ekadashi of the bright fortnight is termed as Padmini Ekadashi and dark fortnight as Parama Ekadashi.