Calendar Science
What Is a Solar Calendar?
A calendar that tracks the year by Earth's orbit around the Sun, rather than the Moon's phases.
The basic unit: the tropical year
A solar year (tropical year) is about 365.24 days — the time for Earth to complete one orbit relative to the seasons. The Gregorian calendar, used worldwide for civil purposes, is a solar calendar, with leap years every four years (skipping century years not divisible by 400) to absorb that extra quarter-day.
India's own solar calendar: Shaka Samvat
India's official National Calendar, Shaka Samvat, is also solar — its months have fixed lengths tied to the Sun's position, unlike the lunar Masa of the religious Hindu calendar. Tamil, Bengali, Odia, Malayalam and several other regional Indian calendars are solar too, which is why regional New Year dates (Puthandu, Poila Boishakh, Vishu) tend to cluster around April 14 each year — a fixed solar transition — rather than shifting with the Moon.
Solar vs. lunisolar in practice
A solar date never drifts against the seasons. A lunisolar date (like most Hindu festivals) can shift by a few weeks year to year but stays broadly anchored to the same season, thanks to the periodic leap month. See our Lunar Calendar page for that mechanism.
Related reading
See Shaka Samvat for India's official solar calendar, or the Indian Calendar overview for how all these systems relate.