Calendar Science
What Is a Lunar Calendar?
A calendar that tracks months by the Moon's phases rather than the Earth's orbit around the Sun.
The basic unit: the synodic month
A lunar month (synodic month) is the time from one new moon to the next — about 29.53 days. Twelve such months make a lunar year of roughly 354 days, about 11 days shorter than the 365-day solar year.
Pure lunar vs. lunisolar
A pure lunar calendar, like the Islamic Hijri calendar, lets months drift freely against the seasons — a 33-year cycle before dates realign. A lunisolar calendar, like the Hindu Panchanga, periodically inserts an extra "leap month" (Adhik Maas) to keep lunar months roughly anchored to the same season year after year.
Where the Sanskrit calendar fits
The Hindu calendar is lunisolar: months (Masa) are lunar, but a leap month keeps festival dates from drifting through all four seasons over time, unlike Islamic dates, which cycle through the whole solar year across roughly 33 years.
Related reading
See Solar Calendar for the counterpart system, or Tithi for how the Hindu calendar measures lunar days specifically.