https://en.m.wikipedia.org/wiki/Yald%C4%81_Night

Yaldā Night (Persian: شب یلدا shab-e yalda) or Chelle Night (also Chellah Night, Persian: شب چلّه shab-e chelle) is an ancient festival in Iran,[1][2] Iraqi Kurdistan,[3][4] Afghanistan,[5] Azerbaijan, Tajikistan, Uzbekistan, Turkmenistan, and Turkey that is celebrated on the winter solstice.[6] This corresponds to the night of December 20/21 (±1) 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)[rs 2] of the Iranian solar calendar.[rs 2]