An Interactive Guide to Tithi

The Hindu calendar is built on precise astronomical principles. These interactive modules break down the fundamental concepts that govern its structure and rhythm.

What is a Tithi?

A Tithi is the time it takes for the Moon's angle to increase by 12° relative to the Sun. Drag the slider to see how the Moon's position and phase define the Tithi. The full 360° cycle is divided into 30 Tithis.

Angle: 0.0°

Tithi: Shukla Pratipadā

Tithi vs. The Solar Day

A Tithi's length varies, while a solar day is fixed at ~24 hours. This timeline shows how a Tithi (white bar) fits within a solar day (sunrise to sunrise). Select a scenario to see how this relationship changes.

Sunrise

Noon

Sunset

Midnight

Sunrise

The Variable Day

The chart shows a typical fluctuation in Tithi duration, caused by the Moon's elliptical orbit. Use the slider to simulate how the cycle's starting point can change month to month.

Cycle Shift:

The Calendar in Practice

The variable Tithi is mapped onto our fixed 24-hour solar day using the Sunrise Rule. This leads to fascinating calendrical events. Click the buttons to see these phenomena.

Sun

Mon

Tue

Wed

Thu

Fri

Sat

(Expanded Day)

(Lapsed Day)

(Normal Calendar)

Click a simulation button to see what happens.

Astrological & Religious Significance

Each Tithi possesses a unique quality. Hover to see a summary, and click to learn more about its nature, ruling planet, and purpose in electional astrology (Muhurta).

First Cycle (Tithis 1-5)

Second Cycle (Tithis 6-10)

Third Cycle (Tithis 11-15)

Click on a Tithi above for more details.

Celestial Rhythms: Daily & Yearly

The daily lag in moonrise and the yearly shift in sunrise are key drivers of the calendar. Explore these two fundamental cycles below.

The Daily Lag: Moonrise vs. Sunrise

The Moon rises about 50 minutes later each day.

The Yearly Shift: Sunrise & Sunset

Based on hypothetical data for Kathmandu, Nepal.

Show Sunset Time

Regional & Cultural Diversity

Why are festivals sometimes celebrated on different days? The answer often lies in two distinct systems for defining a lunar month: Amānta and Pūrṇimānta.

Amānta System (Month ends on New Moon)

Followed in Southern & Western India

Pūrṇimānta System (Month ends on Full Moon)

Followed in Northern India

This animation shows how the same 15-day waning period (*Krishna Paksha*) is assigned to different months in each system. The Pūrṇimānta month begins about 15 days earlier.

Full Moon Mid-Waning New Moon

Phālguna Krishna Paksha (Day 1)

Chaitra Krishna Paksha (Day 1)

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