ayane visuve kuryad
dvadasyam sravanesu ca
navamyam atha kartike
catasrsv apy astakasu
hemante sisire tatha
maghe ca sita-saptamyam
rakaya canumatya ca
masarksani yutany api
dvadasyam anuradha syac
chravanas tisra uttarah
tisrsv ekadasi vasu
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
One should perform the sraddha ceremony on the Makara-sankranti [the day when the sun begins to move north] or on the Karkata-sankranti [the day when the sun begins to move south]. One should also perform this ceremony on the Mesa-sankranti day and the Tula-sankranti day, in the yoga named Vyatipata, on that day in which three lunar tithis are conjoined, during an eclipse of either the moon or the sun, on the twelfth lunar day, and in the Sravana-naksatra. One should perform this ceremony on the Aksaya-trtiya day, on the ninth lunar day of the bright fortnight of the month of Kartika, on the four astakas in the winter season and cool season, on the seventh lunar day of the bright fortnight of the month of Magha, during the conjunction of Magha-naksatra and the full-moon day, and on the days when the moon is completely full, or not quite completely full, when these days are conjoined with the naksatras from which the names of certain months are derived. One should also perform the sraddha ceremony on the twelfth lunar day when it is in conjunction with any of the naksatras named Anuradha, Sravana, Uttara-phalguni, Uttarasadha or Uttara-bhadrapada. Again, one should perform this ceremony when the eleventh lunar day is in conjunction with either Uttara-phalguni, Uttarasadha or Uttara-bhadrapada. Finally, one should perform this ceremony on days conjoined with one’s own birth star [janma-naksatra] or with Sravana-naksatra.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The word ayana means “path” or “going.” The six months when the sun moves toward the north are called uttarayana, or the northern path, and the six months when it moves south are called daksinayana, or the southern path. These are mentioned in Bhagavad-gita (8.24-25). The first day when the sun begins to move north and enter the zodiacal sign of Capricorn is called Makara-sankranti, and the first day when the sun begins to move south and enter the sign of Cancer is called Karkata-sankranti. On these two days of the year, one should perform the sraddha ceremony.
Visuva, or Visuva-sankranti, means Mesa-sankranti, or the day on which the sun enters the sign Aries. Tula-sankranti 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 Vyatipata. On the day when this occurs, one should perform the sraddha 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-sparsa, or a day touched by some portion of three tithis.
Srila Jiva Gosvami has given quotations from many sastras stating that the sraddha ceremony of oblations to the forefathers should not be performed on Ekadasi tithi. When the tithi of the death anniversary falls on the Ekadasi day, the sraddha ceremony should be held not on Ekadasi but on the next day, or dvadasi. In the Brahma-vaivarta Purana it is said:
ye kurvanti mahipala
trayas te narakam yanti
data bhokta ca prerakah
If one performs the sraddha ceremony of oblations to the forefathers on the Ekadasi tithi, then the performer, the forefathers for whom the sraddha is observed, and the purohita, or the family priest who encourages the ceremony, all go to hell.