In Genesis 39–47 there is a description of Joseph captive in Egypt then rising to second in the land and assisting his family during a severe drought. Despite the antiquity of these events it is possible to compare this account with quite a large body of information that has now become available about ancient Egypt at around that time. The Bible date for Joseph being taken as a slave to Egypt is taken here to be around 1838 bc. He would have appeared before Pharaoh around 1825 bc This is during the reign of the12 th dynasty c 1938–1756 bc. The most likely candidate for the Pharaoh during Joseph’s time is Amenemhat III. Fortunately the dates for his reign can be determined quite precisely, using an astronomical observation, known as
the helical rise of Sothis, recorded as occurring during the 7th year of Senusret III. The date for that astronomical event has been calculated at 1872 bc. His son, Amenemhat III, started to reign as co-regent in the 20th year of Senusret III, implying a reign of 1859–1813 bc. The co-regency continued for twenty years until 1840 bc. It is hard to know how accurate the dates are for both the Bible chronology and for the Egyptian calendar, but if the underlying assumptions are correct these dates should be good to within a few years. During the 12th dynasty there was a stable centralised government ruling over all of Egypt. A century later Egypt was in turmoil. Pharaohs often reigned for a year or less. Presumably their friends would have lasted an equally brief period of time. Two centuries earlier it would have been impossible to appoint Joseph the type of position described here. The land was divided up among regional governors who had almost as much power as the Pharaoh.
http://www.revivalfellowship.org.nz/files/Revive%20NZ%20-%20Issue%2014.pdf