Yalda Night 1398

Shab-e Yalda or Shab-e Chelleh ("night of forty") is an Iranic festival celebrated on the "longest and darkest night of the year," Yalda is a winter solstice celebration, that is, in the night of the Northern Hemisphere's winter solstice. 

The longest and darkest night of the year marks "the night opening the initial forty-day period of the three-month winter", from which the name Chelleh, "fortieth", derives.