Mahanavami is the ninth day of Navratri and the third and final day of Durga Puja. On this auspicious day, Goddess Durga is worshipped as Mahisasuramardini which translates into Annihilator of the Buffalo Demon. It is believed that Durga killed the demon Mahishasura after a long drawn out battle, a day after. Thus, the ninth day is dedicated to giving her a holy bath and honouring her with sixteen types of offerings.
Durga Puja performed on Mahanavami is considered equal to worshipping the Goddess on all nine days of Navratri. On this auspicious day, the Siddhidatri form of Durga is worshipped. Girls who have not attained puberty are also worshipped as goddess Durga. Their feet are washed and they are served with puri, chana, kheer and halwa and gifts. Some devotees also observe the Mahanavami Upvas on this day.
RITUALS AND TRADITIONS
On Maha Navami, Durga is offered sugarcane stalks and Navami Homa is performed at the end of the puja. Also, a Maha Arti is organised at the end of the day.
The bhog on Mahanavami consists of fish that is offered to Durga. Later, the devotees have it as part of the prasad. This practice is prominent in areas of Odisha. Other areas of India offer fruits, sweets and halwa puri as bhog to Durga.
Here are the Puja timings, according to drikpanchang.com:
Navami Tithi Begins = 21:36 on September 28, 2017
Navami Tithi Ends = 23:49 on September 29, 2017