Masa (Hindu lunar month)
A masa is a Hindu lunar month, running from one new moon to the next (or full moon to full moon). The 12 months, Chaitra to Phalguna, are named after nakshatras near which their full moons fall.
Also known as: Maas, Mas, Hindu month, Chandra masa
A lunar month lasts about 29½ days. Counting from new moon, the month in which the Sun enters Aries is Chaitra, the one in which it enters Taurus is Vaishakha, and so on through Jyeshtha, Ashadha, Shravana, Bhadrapada, Ashwin, Kartika, Margashirsha, Pausha, Magha and Phalguna. The names echo the nakshatras near each full moon: Chitra for Chaitra, Vishakha for Vaishakha, Krittika for Kartika.
Twelve lunar months fall about 11 days short of a solar year. To keep festivals in their seasons, an extra month, Adhik maas, is added roughly every 32 to 33 months, whenever a lunar month passes without the Sun changing sign.
Regions count months differently. In the amanta system a month ends at Amavasya; in the purnimanta system it ends at Purnima. Tamil Nadu, Kerala, Bengal, Odisha, Assam and Punjab also keep solar months that begin at each Sankranti, so a regional month can differ from the lunar month of the same name.