What is the Bhishma Panchaka Vrata and is it connected to Kartik Poornima pooja?

The Bhishma Panchaka is a five-day fast observed from the 11th (Prabodhini Ekadashi) to the 15th (Kartik Poornima) of the bright half of Kartika. It is named for the great warrior-devotee Bhishma Pitamaha, who observed this vow. Completing this fast and performing a Kartik Poornima pooja on the final day grants merit equivalent to observing the entire month of Karttika vows. Even a partial fast is spiritually beneficial.