GeoGebra Classroom

# The Hindu Lunisolar Calendar

This animation illustrates the basic concepts of the ancient Hindu Lunisolar calendar which is in active use in India even today. By definition, a lunisolar calendar is based on the orbital motion of the Sun and the Moon as observed from the Earth (i.e. in a geocentric model). Saura Mana The solar months (Rashis) are nothing but the familiar signs of the Zodiac, labeled in a different language (Sanskrit). A solar day is defined based on the axial rotation of the Earth:
• One sidereal axial rotation is called a Nakshatra Ahoratra.
• Sunrise to sunrise is called a Savana Ahoratra. This is used in practice today in India.
The "day" which form the basis for this animation (and which is indicated on the animation controls) is the SI Day, i.e. a sidereal solar day. The crossing of the Sun into a Rashi is called a sankramana and Mesha Sankramana marks the beginning of a new solar year (Sauramana Yugadhi). Chandra Mana The lunar days and months are defined based on the position of the Moon relative to the Earth-Sun axis (i.e. its synodic position).
• A lunar month (Masa) starts immediately after New Moon.
• A new fortnight (Paksha) starts immediately after Full Moon.
• Each days (Tithi) is defined as the time required for the Moon to advance 12 successive synodic degrees on its (i.e. relative to the Earth-Sun axis).
You can step through the animation using the incremental controls and observe the effect New Moon and Full Moon have on the calendar:
• New Moon (i.e. Moon is in conjunction with the Sun) starts a new lunar month and the next fortnight
• Full Moon (i.e. Moon is in opposition to the Sun) starts the next fortnight
The Lunisolar Calendar When the lunar calendar is superimposed on the solar calendar the following characteristics are observed:
• The lunar month in which a Mesha Sankramana occurs is designated the first lunar month (Chaitra). Thus, the lunar new year day (Chandramana Yugadhi) is marked by the New Moon immediately preceding the Sauramana Yugadhi.
• Every lunar month witnesses one and only one sankramana (with the exception noted below).