01What Shani Amavasya is
Shani Amavasya, also called Shanishchari Amavasya, is an Amavasya that falls on a Saturday, the weekday of Shani. Like Somvati Amavasya it is a meeting of tithi and weekday, coming up once or twice in most years and occasionally not at all. The tradition gives it to Shani, the slow planet of discipline and consequence, and holds it to be the most fitting day of the year to seek his favour, especially for those going through Sade Sati or a Shani dasha. It keeps the ancestral side of every Amavasya as well, with tarpan for the pitri.
02How the day and time are worked out
The page takes each Amavasya on the day the new moon tithi holds at sunrise, as the Amavasya list does, and keeps the ones whose day is a Saturday. The weekday follows that rule, not the moment the tithi starts: an Amavasya that begins on a Saturday afternoon and holds the Sunday sunrise is a Sunday Amavasya, while one that began on Friday and is still current at sunrise on Saturday is Shani Amavasya. A tithi ending close to dawn can fall on either side of sunrise in different cities, so the list is worked out for the one you choose.
03How it is kept
Shani temples draw large crowds on the day, and the offerings are dark and simple: mustard or sesame oil poured over the image of Shani or a Shani stone, black til, black urad, a dark cloth and iron. Many light a mustard oil lamp under a peepal tree after sunset and recite the Shani Chalisa or the Shani stotra of Dasharatha. Charity is central, given to labourers and to those in need, because the tradition links Shani with service. Hanuman is worshipped too, after the account in which he freed Shani from the prison of Ravana. Tarpan for the pitri completes the day.
04The rest of the calendar