The Solar Hijri calendar, also called the Shamsi Hijri calendar, and abbreviated as SH, is the official calendar of Iran and Afghanistan. It begins on the vernal equinox. Each of the twelve months corresponds with a zodiac sign. The first six months have 31 days, the next five have 30 days, and the last month has 29 days in usual years but 30 days in leap years. The year of Prophet Muhammad's migration to Medina (622 CE) is fixed as the first year of the calendar, and the New Year's Day always falls on the March equinox.