Tithi

Because the moon's speed varies, tithis are not equal in length — they range from roughly 19 to 26 hours, so a tithi can begin and end at different clock times each day. The 30 tithis split into two halves of 15 each: Shukla Paksha (waxing fortnight from new to full moon) and Krishna Paksha (waning fortnight from full to new). Each tithi is associated with a presiding deity and a recommended type of activity — for example, Pratipada (1st tithi) is good for new beginnings, Chaturthi (4th) is sacred to Ganesha, Ekadashi (11th) is for fasting and spiritual practice, and Amavasya (new moon) is treated as inauspicious for new ventures but auspicious for ancestor rites.