The time of Islamic festivals is calculated according to local sightings of various phases of the moon and the dates given below are approximations which are subject to change each year.
Iran has a variable climate. In the northwest, winters are cold with heavy snowfall and subfreezing temperatures during December and January.
There is a vastly extended network of rivers in Iran most of which seasonally are filled with water. Some permanent rivers run from the Alborz or the Zagros to the Caspian Sea, Persian Gulf and Oman Sea.