"Winter Feast: Yalda Night" is an ancient Iranian festival originally celebrated on the Northern Hemisphere's longest night of the year, that is, on the eve of the Winter Solstice. The winter solstice occurs at the instant when the Sun's position in the sky is at its greatest angular distance on the other side of the equatorial plane from the observer. The Winter Solstice occurs on December 20 or 21 each year.
Yalda is the most important non-new-year Iranian festival that comes back to the 2nd millennium BC. According to Persian mythology, Mitra, the Godess of love, was born at the end of this night after the long-expected defeat of darkness against light. The seasonal significance of the winter solstice is in the reversal of the gradually lengthening nights and shortening days. Happy Yalda everybody!