Angarak Vinayaka Chaturthi is dedicated to Lord Ganesha and is observed on the fourth day after Amavasi (No moon day). Also known as Angaraki Vinayaki Chaturthi, this auspicious day happens when Chaturthi after Amavasi falls on a Tuesday.
The monthly Chaturthi after Amavas (fourth day during waxing phase of moon) is Vinayaka Chaturthi for Ganesha devotees. Some staunch Ganesh devotees observe a fast from sunrise to sunset on the day.
Usually, the monthly fast on Chaturthi is observed during the Chaturthi that falls after Purnima and it is popularly known as Sankashta or Sankatahara Chaturthi.
Popular belief is that observing Chaturthi Vrat will bring prosperity, happiness and fulfillment of desires. The greatness of Chaturthi Vrata dedicated to Lord Ganesha was explained by Lord Krishna to Yudhishtira, the eldest of the Pandavas. It is also detailed in the Narasimha Purana and Bhavishaya Purana.