Mandala Pooja at Sabarimala Ayyappa Temple is observed on 11th or 12th day during Dhanu Masam.
Mandala Pooja is the last day of 41 days long austerity observed by devotees of Lord Ayyappa. The fasting begins 41 days before Mandala Puja i.e. on the first day of Vrishchikam Masam according to Malayalam Calendar.
Mandala Puja and Makar Vilakku are the two most famous events at Sabarimala Ayyappa temple when the temple is kept open for devotees for most of the days.