Today, on the fifth day of ongoing Shardiya Navratri, the sixth avatar of Nav Durga — Goddess Katyayani will be worshipped instead of the fifth one, Goddess Skandamata. The Shashti Tithi (sixth day) of Shardiya Navratri this year is on October 11. As per the legend, Devi Parvati took the Avatar of Katyayani to kill the demon Mahishasura.