Sadæ is the great Zoroastrian-Iranian winter festival that heralds the coming of spring, and the gradual warming of the waters, the earth and plants. Sadæ is celebrated forty days after winter solstice, on or about January 30th.
The festival of Sadæ is celebrated by making huge bonfires near running water or a sacred spring, and by drinking red wine with noghl or sugar coated almonds. Noghl is made by boiling sugar in rose water, and coating roasted almonds in the mixture.
The festival of Sadæ has been forgotten among the Parsi Zoroastrians of India, but Iranian Zoroastrians are still celebrating Sadæ as a major part of their religious observances.
It is believed in folklore that on the night of Sadæ the winter comes out from hell (Biruni, Āṯār, tr. Sachau, p. 226; Qazvini, p. 80) and, according to Biruni, in the City Karaj this night is called šab-e gazina (the biting night).
The etymology of the word sadæ is generally derived from the numeral sat (one hundred). Interestingly, the Indo European languages are divided into “satem” languages, from the Avestan word satəm “hundred,” and “centum” or westerly languages after Latin word for hundred or centum.
The memory of the 150-days or 5 months of winter divided by sadæ in two unequal parts of 100 days celebrated on sadæ, and 50 days from Sadæ Spring Equinox can still be found in popular sayings, such as “ṣad bae Sadæ, panjāh be Nauvrooz (One hundred days that is Sadæ, from here 50 more days left to Nauvrooz or Spring Equinox.)
Since Sadæ is considered to be the coldest night of the year, and on Sadæ night the frost and freezing cold suppose to come out from hell, it is possible that sadæ is etymologically related to Avestan çared “cold.” Sadæ night is also called šab-e gazina (the biting/frost night.)
The great scholar Mary Boyce mentions a major fire festival still observed by Iranian Zoroastrians which falls hundred days before Nauvrooz or Spring Equinox. This festival is named Sadæ in Kermán and Hīrômbáii in Yazd. Mary Boyce (1968, pp. 201-12; Idem, 1983, pp. 800-1) concludes that Sadæ festival honors of the Zoroastrian yazata/god being of Rapiṯwin, the lord of Summer and Mid-day, who rules over the warm part of the year (that is, the seven summer months) and then descends under the ground in order to reappear on the first day after Spring Equinox. The ceremonies of Rapiṯwin farewell and welcome are observed by the Zoroastrians. Rapiṯwin is believed to make the plants grow and the fruit ripen, and, while underground, Rapiṯwin heats the roots and the underground waters from beneath, thus protecting the plants from cold. Accordingly, the bonfires festival of Sadæ help Rapiṯwin “the Lord of Mid-Day” to heat the earth and plant roots during the most severe cold bites and freezes. That is why Zoroastrians light their Sadæ bonfires near running water, sacred spring or over an underground canal (qanāt).
This practice is confirmed by a description of fire reflected in water as part of the literary pattern, as can be seen in the poems by Manṣuri-Samarqandi (Jašn-e Sada, pp. 58-59),. The ancient Sadæ festival poems provide an exquisite description of fire, which frequently compares the energy of fires to a plant, a flower, a fruit tree, a stack of corn, or a garden blossoming in a winter landscape. This imagery seems to go back to even older mythological concepts connecting the plant life with fire energy, (See the Poetic Gathas Yasna 48.6 and Yasna 49.8 for example.)
Point is that the folkloric motif of Winter-and-Spring combat, and of the return of an energetic god power is predominant in Sadæ bonfire rituals. Simone Cristoforetti (1995) also stresses the dragon-killing motif of the Sadæ mythology and its broadly understood “ambrosian” aspects as conceived by G.Dumézil in his early works (1926, 1929).