The word ayana means "path" or "going." The six months when the sun moves toward the north are called uttarāyaṇa, or the northern path, and the six months when it moves south are called dakṣiṇāyana, or the southern path. These are mentioned in Bhagavad-gītā (8.24-25). The first day when the sun begins to move north and enter the zodiacal sign of Capricorn is called Makara-saṅkrānti, and the first day when the sun begins to move south and enter the sign of Cancer is called Karkaṭa-saṅkrānti. On these two days of the year, one should perform the śrāddha ceremony.
Viṣuva, or Viṣuva-saṅkrānti, means Meṣa-saṅkrānti, or the day on which the sun enters the sign Aries. Tulā-saṅkrānti is the day on which the sun enters the sign Libra. Both of these days occur only once within a year. The word yoga refers to a certain relationship between the sun and moon as they move in the sky. There are twenty-seven different degrees of yoga, of which the seventeenth is called Vyatīpāta. On the day when this occurs, one should perform the śrāddha ceremony. A tithi, or lunar day, consists of the distance between the longitude of the sun and that of the moon. Sometimes a tithi is less than twenty-four hours. When it starts after sunrise on a certain day and ends before the sunrise of the following day, the previous tithi and the following tithi both "touch" the twenty-four-hour day between the sunrises. This is called tryaha-sparśa, or a day touched by some portion of three tithis.
Śrīla Jīva Gosvāmī has given quotations from many śāstras stating that the śrāddha ceremony of oblations to the forefathers should not be performed on Ekādaśī tithi. When the tithi of the death anniversary falls on the Ekādaśī day, the śrāddha ceremony should be held not on Ekādaśī but on the next day, or dvādaśī. In the Brahma-vaivarta Purāṇa it is said:
- ye kurvanti mahīpāla
- śrāddhaṁ caikādaśi-dine
- trayas te narakaṁ yānti
- dātā bhoktā ca prerakaḥ
If one performs the śrāddha ceremony of oblations to the forefathers on the Ekādaśī tithi, then the performer, the forefathers for whom the śrāddha is observed, and the purohita, or the family priest who encourages the ceremony, all go to hell.