Tithi

In vedic timekeeping, a tithi (also spelled thithi) is a lunar day, or the time it takes for the longitudinal angle between the moon and the sun to increase by 12°. Tithis begin at varying times of day and vary in duration from approximately 19 to approximately 26 hours.

There are 30 tithis in each lunar month, named as follows:

  Krsna paksa[?]                        Gaura paksa
  (dark fortnight)                   (bright fortnight)
  1   Pratipat                       1   Pratipat
  2   Dvitiya                        2   Dvitiya
  3   Trtiya                         3   Trtiya
  4   Caturthi                       4   Caturthi
  5   Pancami                        5   Pancami
  6   Sasti                          6   Sasti
  7   Saptami                        7   Saptami
  8   Astami                         8   Astami
  9   Navami                         9   Navami
 10   Dasami                        10   Dasami
 11   Ekadasi[?]                       11   Ekadasi[?]
 12   Dvadasi                       12   Dvadasi
 13   Trayodasi                     13   Trayodasi
 14   Caturdasi                     14   Caturdasi
 15   Amavasya (new moon)           15   Purnima (full moon)

Ekadasi[?], the eleventh day of each lunar fortnight[?], has special religious significance in Hinduism and Jainism—usually observed by fasting.