Shani Dev
If a trayodasi(13th day of the Telugu month) falls on a Saturday it is treated as sani trayodasi.
Sani is one among the nine grahas which are a part of the astrology chart. And it is believed that the movement of these navagrahas is the cause of our destiny.
Sani is believed to be the one who would cause a lot of damage to our prosperity and hence needs to be satisfied the most.
This day is considered to be a day on which Lord Sani could be pleased easily. On this the persons who are affected by Sani (Elnati Sani, Alenati Sani, Ardhashtama Sani, Ashtama Sani etc) are adviced to visit a Navagraha temple and perform Tailabhishekam (bathing the Lord Sani with Gingerly Oil).
On this day it is adviced to donate 50gm Blackgram,100ml Gingerly Oil,100gm Coal, a small black cloth,8 iron nails and some navadhnyam (nine types of cerals) all tied in a cloth to Brahmin. On this day it is advised not to purchase Oil,Leather,Navadhanyalu etc.
It is good if one could visit Sani Shingnapur near Shiridi to pray to Lord Shani.
