Iranian women buy sweets for Yalda Night at a market in Tehran. Yalda Night is Iranian winter solstice celebration. It is celebrated on the longest night for the year, locally believed, to be on the eve of winter solstice. Iranians buy fruits for Yalda Night at a market in Tehran. Yalda Night is Iranian winter solstice celebration. It is celebrated on the longest night for the year, locally believed, to be on the eve of winter solstice.