Significance of Sankashti and Vinayaki Chaturthi - According to Hindu lunar calendar, there are two Chaturthi Tithis in every month. The days of Chaturthi are dedicated to Lord Ganesha. The Chaturthi that falls after Amavasya or new moon during Shukla Paksha is observed as “Vinayaki” or “Vinayaka Chaturthi” and the one after Purnima or full moon during Krishna Paksha is observed as “Sankashti Chaturthi”. In other terms, every fourth day (chaturthi) of the bright fortnight in every lunar month is Vinayaki Chaturthi and that of the dark fortnight is Sankashti Chaturthi.
Although Vinayaka Chaturthi Vratam/ fasting is done every month but the most significant Vinayaki Chaturthi falls in month of Bhadrapada. Vinayaki Chaturthi that falls during the month of Bhadrapada is known as “Ganesha Chaturthi” and is celebrated as the birthday of Lord Ganesha throughout the world.