Iranian Calendar (Jalali Calendar)
The Iranian calendar (also known as Persian calendar or the Jalaali Calendar) is a solar calendar currently used in Iran and Afghanistan. It is observation-based, rather than rule-based, beginning each year on the vernal equinox as precisely determined by astronomical observations from Tehran.
The Gregorian calendar is the calendar that is used nearly everywhere in the world. A modification of the Julian calendar, it was first proposed by the Neapolitan doctor Aloysius Lilius, and was decreed by Pope Gregory XIII, for whom it was named, on 24 February 1582.
Islamic Calendar (Hijri Calendar)
The Islamic calendar or Muslim calendar (also called "Hijri calendar") is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days. It is a lunar calendar having 12 lunar months in a year of about 354 days. Because this lunar year is about 11 days shorter than the solar year, such as a year of the Jalali or Gregorian calendar.