<P> The date of Hajj is determined by the Islamic calendar (known as Hijri calendar or AH), which is based on the lunar year . Every year, the events of Hajj take place in a five - day period, starting on 8 and ending on 12 Dhu al - Hijjah, the twelfth and last month of the Islamic calendar . Among these five days, the 9th Dhul - Hijjah is known as Day of Arafah, and this day is called the day of Hajj . Because the Islamic calendar is lunar and the Islamic year is about eleven days shorter than the Gregorian year, the Gregorian date for Hajj changes from year to year . Thus, each year in the Gregorian calendar, the pilgrimage starts eleven days (sometimes ten days) earlier than the preceding year . This makes it possible for the Hajj season to fall twice in one Gregorian year, and it does so every 33 years . The last time this phenomenon occurred was 2006 . The table below shows the Gregorian dates of Hajj of recent years (the dates correspond to 9 Dhul - Hijjah of Hijri calendar): </P> <Table> <Tr> <Th> 2011 </Th> <Th> 2012 </Th> <Th> 2013 </Th> <Th> 2014 </Th> <Th> 2015 </Th> <Th> 2016 </Th> <Th> 2017 </Th> </Tr> <Tr> <Td> 5 November </Td> <Td> 25 October </Td> <Td> 14 October </Td> <Td> 3 October </Td> <Td> 23 September </Td> <Td> 11 September </Td> <Td> 31 August </Td> </Tr> </Table> <Tr> <Th> 2011 </Th> <Th> 2012 </Th> <Th> 2013 </Th> <Th> 2014 </Th> <Th> 2015 </Th> <Th> 2016 </Th> <Th> 2017 </Th> </Tr> <Tr> <Td> 5 November </Td> <Td> 25 October </Td> <Td> 14 October </Td> <Td> 3 October </Td> <Td> 23 September </Td> <Td> 11 September </Td> <Td> 31 August </Td> </Tr>

When is hajj performed what are some of the things pilgrims do