THITHI: Thithi is nothing but the angle formed by Sun and Moon.
When Sun and Moon are together at the same degree it is called Amavasya or New Moon Day. As Moon travels away from Sun, at each12 degree of difference , a new Thithi is formed. When the difference is 180 degrees it is Poornima or Full Moon Day.
Thithi = (Long of Moon – Long of Sun) / 12
In all there are 30 Thithis. 15 in Bright half (Sukla paksha ) and 15 in Dark half (
1-6-11 are Nanda thithis
2-7-12 are Badra thithis
3-8-13 are Jaya thithis
4-9-14 are Riktha thithis (Inauspicious)
5-10-15/30 are Poorna Thithis
Thithi: KSHAYA: If a Thithi starts after Sun rise and ends before next Sun rise, it is called Thithi Kshaya or (loss of Thithi). It should be avoided in all good Muhurtas.
Thithi : VRIDHI : If a Thithi prevails at the Sun rise time or in other words, if a Thithi starts before one Sun rise and ends after next Sun rise , it is called Thithi Vridhi. It should also be avoided in all good Muhurtas
Thithi : GANDANTHA : The ending one ghati of Poorna Thithi and starting one ghati ( 24 ‘ ) of Nanda Thithi are called junction points or Thithi Gandantas. These should be avoided for Muhurtas.