Shani Jayanthi is usually on Amavasya in Vaishakh month or Vaishakha Masam, while it falls on Jyeshta Amavasya according to the North Indian calendars.
Shani Jayanti is celebrated as the birthday of Lord Shani, one of the navagrahas or nine gods of Hinduism. According to Hinduism, Shani is the god of Shanivar. Lord Shani is also known as Shaneeswaran, Sani dev, Sanichara bhagawan or Chaya Putra.
Prayers to Lord Shani are considered as an essential feature of ones prospective plans to avoid or mitigate the Shani Dosham (bad effects from Lord Shani depending upon ones birth chart). Shani Puja is an important practice for Hindu astrological followers. Shani Thailabhishekam and Shani Puja are the primary formalities practiced during Shani Jayanthi, Shani Amavasya and Shani Trayodashi.
As believed by many, Lord Shani does not always bring troubles to the people but is also a well wisher and a friend as well. Lord Shani often portrays multiple roles only to make people realize that there is God and one has to submit with complete honesty and belief. The deity is often depicted as a strong person with dark complexion and rides on a crow with a bow and an arrow in his hands.