In a Hindu calendar, Tithi means a lunar day. New moon or no moon or Amavasya occurs when the longitudes of the moon and the sun are equal. When the moon moves 12 degrees east from the sun, a Thithi is calculated. This is known as Pratipada Thithi and it is the first Tithi. It comes during Shukla Paksha, the moon’s waxing phase. Pournami or full moon occurs when the moon moves 180 degrees, and when the moon moves 360 degrees, Amavasya comes again.
In a fortnight, there are 15 Tithis.
How long is a Tithi?
The movements of the sun and the moon keep varying in speed. Hence, the length of a Tithi keeps changing. A tithi can be upto 26 hours in length, and it can be as less as 21 hours 34 minutes and 24 seconds. The time a tithi begins alters with the general time followed in each country.
Sometimes a tithi can begin and end on the same day. In that case, there will be two tithis in one day. For instance, one may see a Tritiya and Chaturthi on the same day
Sometimes a tithi can overlap into the following day. In that case, there will be two same tithis on two consecutive days. For instance, it will be Tritiya on Sunday and Monday.
Those days that have two Beginning or End points of tithis are regarded as inauspicious. The same applies if there are no beginning or end points of tithis.
The thirty Tithis that occur in a month are:
1. Pratipada, Padya or Parthami, the first day after Amavasi
2. Dwitiya
3. Tritiya
4. Chaturthi
5. Panchami
6. Shasti
7. Saptami
8. Ashtami
9. Navami
10. Dasami
11. Ekadashi
12. Dwadashi
13. Trayodashi
14. Chaturdashi
15. Purnima or full moon
16. Partipada
17. Dvitiya
18. Trithiya
19. Chaturti
20. Panchami
21. Sashti
22. Saptami
23. Ashtami
24. Navami
25. Dasami
26. Ekadashi
27. Dwadashi
28. Triodashi
29. Chaturdashi
30. Amavasya or No Moon or New Moon
Deities that rule Tithis
Each tithi is ruled by a deity. Understanding the deities that rule the various Tithis is helpful to understand the energy and vibrations of the respective Tithis. For example, Pournami/Purnima is ruled by Naaga, which indicates the secretive side of this
Tithi.
The Deities ruling the Tithis are in order, (S1) Brahma, (S2) Agni, (S3) Virinchi, (S4) Vishnu, (S5) Gauri, (S6) Ganesha, (S7) Yama, (S8) Sarpa, (S9) Chandrama, (S10) Kaartikeya, (S11) Surya, (S12) Indra, (S13) Mahendra, (S14) Vaasava, (P) Naaga, (K1) Durga, (K2) Dandadhara, (K3) Shiva, (K4) Vishnu, (K5) Hari, (K6) Ravi, (K7) Kaama, (K8) Shankar, (K9) Kalaadhara, (K10) Yama, (K11) Chandrama, (K12) Vishnu, K(13) Kaama, (K14) Shiva, and (A) Pitrs.
In the above, S stands for Shukla Paksha, K for Krishna Paksha, P for Pournami, and A for Amavasya.
Read more : https://www.astroved.com/astropedia/en/tithi-today
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