Shab-e Yalda is a Persian festival celebrated on the “longest and darkest night of the year,” that is, in the night of the Northern Hemisphere’s winter solstice. Calendrically, this corresponds to the night of December 20/21 in the Gregorian calendar, and to the night between the last day of the ninth month (Azar) and the first day of the tenth month (Dey) of the Iranian civil calendar.