Masa & Ritu

The Hindu calendar is lunisolar. Months (Masa) are primarily lunar — each month spans one New Moon to the next (Amanta system) or one Full Moon to the next (Purnimanta system). The month name is derived from the Nakshatra in which the Full Moon falls. Seasons (Ritu) follow the solar cycle: 6 Ritus of 2 months each track the Sun's progression through the zodiac. A solar year has ~365.25 days, while 12 lunar months total only ~354 days. The ~11-day gap is resolved by intercalation — an extra "Adhika Masa" (leap month) is inserted roughly every 2.7 years when two New Moons fall within the same solar month.