Chaturthi

Chaturthi or Chaviti (Telugu: చతుర్థి or చవితి), is the fourth day (Tithi) of any lunar month in the Hindu calendar.

During each month, Lord Ganesha is worshiped with a different name and peeta (Lotus petals). On the Charturti day (4th day after new moon) of each month, the 'Sankashta Ganapathi Pooja' prayer is performed. Each ‘Vratha’ (strict fast) has a purpose and is explained to us by a story known as the ‘Vratha Katha’. This prayer offering has 13 Vratha Kathas, one for each month and the 13th story is for 'athika' (The Hindu calendar has one extra month every 4 years). The uniqueness of this Vratha is that the story pertaining to that month alone has to be recited.

The Sankasta Ganapathi Pooja - 13 Names and Peetas

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Wikipedia