The Concept and Significance of Tithi (Lunar Day)

Introduction

To understand Tithi, you first need to understand Masa and Paksha clearly.

If we divide a Masa into 30 equal parts, each slice represents a Tithi.

How long is a Tithi? 🕰️

A Masa is about 29.53 days long. If we divide this by 30, we find that each Tithi is about 23 hours and 36 minutes long. This is close to, but not exactly, one day.

Tithi and the Moon-Sun Angle 📐

• The 360-degree Cycle: The Moon's complete cycle, returning to the same phase, is like a 360-degree turn. As there are 30 Tithi, each Tithi represents a 12-degree slice of this 360-degree pie (i.e. `360/30 = 12`).
• Angular Separation 📐 : A Tithi starts when the angle between the Moon and the Sun increases by 12 degrees. For example, if you imagine the Moon and the Sun as two points in the sky, each Tithi occurs as the Moon 'moves' 12 degrees away from the Sun.
• Variation in Length: Because the Moon's path around Earth and Earth's path around the Sun are not perfect circles but slightly oval ⬭ (eccentric), the time it takes for this 12-degree shift can vary quite a bit. A Tithi can be as short as 21 hours and as long as 26 hours. These variations mean that the duration of a Tithi is not constant and can vary considerably over the course of the year.

Practical Implications

• Timing: Because a Tithi is not exactly aligned with our regular 24-hour days, it can start and end at any time of the day. For instance, a Tithi might start in the middle of an afternoon and end in the middle of the next afternoon.

Names of Tithi

We know that each masa has two halves - Shukla Paksha and Krishna Paksha

Each Tithi belongs either to Shukla Paksha or to Krishna Paksha. In both these paksha, we count the Tithis from one to fifteen, using Sanskrit number names.

Shukla Paksha (Waxing Phase)

1. Prathama/Pratipada (First)
2. Dwitiya (Second)
3. Tritiya (Third)
4. Chaturthi (Fourth)
5. Panchami (Fifth)
6. Shashti (Sixth)
7. Saptami (Seventh)
8. Ashtami (Eighth)
9. Navami (Ninth)
10. Dashami (Tenth)
11. Ekadashi (Eleventh)
12. Dwadashi (Twelfth)
13. Trayodashi (Thirteenth)
14. Chaturdashi (Fourteenth)
15. Purnima (Full Moon) 🌕

Krishna Paksha (Waning Phase)

1. Prathama/Pratipada (First)
2. Dwitiya (Second)
3. Tritiya (Third)
4. Chaturthi (Fourth)
5. Panchami (Fifth)
6. Shashti (Sixth)
7. Saptami (Seventh)
8. Ashtami (Eighth)
9. Navami (Ninth)
10. Dashami (Tenth)
11. Ekadashi (Eleventh)
12. Dwadashi (Twelfth)
13. Trayodashi (Thirteenth)
14. Chaturdashi (Fourteenth)
15. Amavasya (New Moon) 🌑

Tithi  Vriddhi and Tithi Kshaya

Unlike the regular Gregorian 24-hour day, a Tithi can be shorter or longer. It can last from about 21 hours to 26 hours. This happens because of the way the Moon and Earth move.

Vaara is a solar day in the Hindu calendar, similar to our regular day. It usually lasts about 24 hours. But instead of starting at midnight 🕛 like in the Gregorian Calendar, in the Hindu calendar, it starts at sunrise 🌅 and ends at the next sunrise 🌅.

Matching Tithi with Vaara

Since a Tithi can start and end at any time, we look at the Tithi at sunrise to decide what Tithi the Vaara (day) is. This can lead to different situations. Let us use some simplified, fictional examples to understand:

1. One Tithi in a Vaara - Tithi Vriddhi:

Example: Suppose on a Sunday (Ravivaara), the sunrise is at 6 AM. On that day Panchami begins at 5:45 AM. So Ravivaara is marked as Panchami. The sunrise on Monday (Somavaara) is at 6 AM as well. The panchami continues till 6:15 AM on Somavaara and Shashthi Tithi begins after that. So, Somavaara is marked as Panchami as well. The total duration of Panchami Tithi is 24h 30m, which is more than 24 hours. If a Tithi is beginning before sunrise, and remains till next sunrise then this situation is called as Tithi Vridhi.

2. Two Tithis in a Vaara - The Usual Case:

Example: Suppose on a Sunday (Ravivaara), the sunrise is at 6 AM. On that day, Panchami begins at 5:45 AM. So Ravivaara is marked as Panchami. The sunrise on Monday (Somavaara) is at 6 AM as well. The panchami continues till 5:15 AM on Somavaara, and Shashthi Tithi begins after that. So, Somavaara is marked as Shashthi. The total duration of Panchami Tithi is 23h 30m. This is the most common case.

3. Three Tithis in a Vaara - Tithi Kshaya:

Example: Suppose on a Sunday (Ravivaara), the sunrise is at 6 AM. On that day Panchami only begins at 6:45 AM. So Ravivaara is marked as Chaturthi (the day before Panchami). The sunrise on Monday (Somavaara) is at 6 AM as well. The panchami continues only till 5:15 AM on Somavaara and Shashthi Tithi begins after that. So, Somavaara is marked as Shashthi, not as Panchami. So, Panchami is not marked at all - the tithi is "skipped". The total duration of Panchami Tithi is 22h 30m, which is less than 24 hours. If a Tithi starts after sunrise and ends before sunrise on the next day then this is known as Tithi Kshaya.