Sizdeh Bedar is celebrated on this 13th day of the Persian new year
Sizdahbedar or Sizdah Bedar (also frequently stylized as "13 Bedar") (Persian: Sizdah Bedar) is the name of a festival in Persian Culture.
Sizdah Bedar is the day Tir (The Blessed day) of the month Farvardin from ancient Persian (Iranian) calendar, which is the first day of agricultural activity of Ancient Persians. Be-dar in Persian means, going out. In this day Iranians go to have fun with their families all the day long, in some sub cultures they have 14 Be-Kaar, which means 14 to work. During recent years, Jewish-Islamic people have related 13 Be-dar as the unlucky 13, which isn't related to ancient Persian culture, one of the reasons for such interpretation is that in some years, 13 Farvardin is the same as April 1 (April Fools' Day).
Sizdeh Bedar is celebrated in Iraq, Armenia, Azerbaijan, Central Asia, and elsewhere. An increasing number of participants are taking part in the holiday. In cities like Los Angeles with large populations of Iranians, a growing number of parks are set up by the city to accommodate the large number of people.