Iranian celebrated last night of fall on December 21st as longest night of year from before of Islam and we still celebrate Yalta night.
(read more)Iranian family gather this night, stay awake until late night ,have dry fruit and seed, special feast(maybe fish and rice) and talks about everything and listen to stories that grand fathers told (I think this days swap with popular TV shows).
Iranian for thousand years celebrate these nights as one of many special occasions that they had like Norooz, Mehregan, and... but today we only celebrate this night and Norooz (Iranian new year) as a Iranian tradition.
I hope at least these tow Iranian occasion (which are still alive) don't forget with western occasions like valentine and Halloween. (Valentine became very popular among youth in Iran these years)
you can see some cartoon about Yalda Night here