jyotisha and the sky
What is the Hindu solar calendar and how does it differ from the lunar calendar?
The solar calendar
The Hindu solar calendar, called Saura, is built around the Sun's journey through the twelve rashis, the zodiac signs. When the Sun moves into the first rashi, Mesha, that moment is called Mesha Sankranti. In many parts of India it marks the solar new year. Tamil Nadu, Kerala, and Bengal each have their own solar calendar with their own names and customs, but all of them follow this same idea of tracking the Sun's transit. Dates in a solar calendar fall on roughly the same day each year in the common international calendar.
The lunar calendar
The lunar calendar is built on tithis, the thirty phases of the Moon in each month. A lunar month runs from one new moon to the next, or in some traditions from full moon to full moon. Because twelve lunar months add up to fewer days than a solar year, the lunar calendar slowly drifts against the seasons. To fix this, most Hindu traditions use a lunisolar system. Every thirty-two months or so, an extra month is added. This is called Adhika Masa, sometimes called the leap month. It brings the lunar count back in line with the Sun and the seasons.
Why both matter
The Sun and Moon each carry their own meaning in the tradition. The Sun is linked to time, order, and the outer world. The Moon is linked to the mind, emotion, and the inner life. Festivals tied to the Sun, like Pongal or Onam, celebrate the harvest and the seasons. Festivals tied to the Moon, like Diwali or Holi, are fixed by the tithi, the Moon's phase on a particular day. This is why the same festival can fall on different dates in the common calendar each year.
Regional differences
The Panchanga, the traditional almanac, brings solar and lunar reckoning together. But different regions lean on one more than the other. South Indian states like Tamil Nadu and Kerala have long followed the solar calendar for their new year and major festivals. Much of North and Central India follows the lunar calendar more closely for everyday religious life. Bengal sits in between, with a solar calendar for its new year but lunar tithis for many festivals. There is no single Hindu calendar. The tradition holds many regional systems side by side.
In the diaspora today
For Hindus living far from their home communities, the Panchanga is often the main guide. Many families follow the calendar of the region their family comes from, so a Tamil family and a Gujarati family may celebrate new year on completely different days. Online Panchangas and temple announcements now help communities abroad keep track of both solar and lunar dates together.