- The Hindu calendar is entirely based on astronomy and tracks the movement of two primary celestial bodies: the sun and moon
- It uses a geocentric model of the solar system, which places Earth at the center
- The source of these astronomical calculations is the Surya Siddhanta, an ancient scientific treatise written around 400 AD
- Based on both solar and lunar movements
- Contains multiple elements including:
- Uttarayana and Dakshinayana
- Various months