What is BC (before Christ) and AD (Anno Domini)?

Most cultures start the calculation of their time with an event that was important for them. For the Christians this was the birth of Jesus Christ. The year of birth of Christ is also known as ‘turn of the eras’ because there is a belief among the Christians that with the birth of Jesus Christ a ‘new time’ started. The counting of years was started again from one after this time. Everything that happened earlier was specified as ‘before Christ’ or ‘BC’. The Islamic calendar starts when the Prophet Mohammed left Mecca in AD 622. In addition, one year of the Islamic calendar is shorter than that of the Christian calendar since it ends after nine new moons. On July 20, 2012, the calendar of the Muslims will show September 1, 1433, and hence the first day of the fasting month of Ramadan.