Significance
Magha Gupt Navratri is one of the two 'Gupt' (secret) Navratris of the year, falling in the winter month of Magha. Unlike the public celebration of Chaitra and Sharad, it is observed quietly and is prized by tantriks and sadhaks for intense Shakti and Dasha-Mahavidya sadhana.
Rituals
Devotees begin with Ghatasthapana and observe nine days of fasting, silent japa, and worship of the Goddess — many following esoteric Mahavidya practices. Ordinary devotees keep it like the other Navratris, worshipping the nine forms of Durga.
How the dates are fixed
Magha Gupt Navratri runs nine consecutive nights from the Pratipada of Magha Shukla paksha to Navami; the Ghatasthapana muhurat is set on the first day for your location.