Ancient Egyptians

The Ancient Egyptians had a limited knowledge of astronomy. Part of the reason for this is that their geometry was limited, and did not allow for complicated mathematical computations. Evidence of Ancient Egyptian disinterest in astronomy is also evident in the number of constellations recognized by Ancient Egyptians. At 1100 BC, Amenhope created a catalogue of the universe in which only five constellations are recognized. They also listed 36 groups of stars called decans. These decans allowed them to tell time at night because the decans will rise 40 minutes later each night. Theoretically, there were 18 decans, however, due to dusk and twilight only twelve were taken into account when reckoning time at night. Since winter is longer than summer the first and last decans were assigned longer hours. Tables to help make these computations have been found on the inside of coffin lids. The columns in the tables cover a year at ten day intervals. The decans are placed in the order in which they arise and in the next column, the second decan becomes the first and so on.

Astronomy was also used in positioning the pyramids. They are aligned very accurately, the eastern and western sides run almost due north and the southern and northern sides run almost due west. The pyramids were probably originally aligned by finding north or south, and then using the midpoint as east or west. This is because it is possible to find north and south by watching stars rise and set. However, the possible processes are all long and complicated. So after north and south were found, the Egyptians could look for a star that rose either due East or due West and then use that as a starting point rather than the North South starting point. This would result in the pyramids being more accurately aligned with the East and West, which they are, and all of the errors in alignment would run clockwise, which they do. This is because of precession of the poles