Astronomy is fundamental to Bauval's Correlation Theory. Over a cycle of 26 000 years the Earth wobbles slightly on its axis and this leads to an apparent change in the position of the stars. This phenomenon is known as Precession -- the stars precess one another in Declination, their relative position in the sky. This is best described with the aid of the adjacent diagram.As the Earth wobbles the Pole Star that marks the approximate Celestial Pole changes. Polaris marks the spot now, but at the time of the Pyramids it was marked by Thuban in the constellation of Draconis. In 12 000 AD Vega in the constellation of Lyra will mark the Pole.
A further change in the stars' actual position is caused by the expanding Universe. Stars are not stationary in space -- they have what is termed Proper Motion. Some stars are moving towards Earth while others are moving away. Groups of related stars like the Belt Stars of Orion tend to move together through space.
The rate of change of a star's position from the observer's location is a function, among other things, of its distance. Stars that are very distant appear to move more slowly. This is the case with the Belt Stars which lie approximately 1400 light years from Earth. Thus, over the centuries, they have changed in Declination dramatically, causing them to rise and set at widely differing times. They retain their characteristic shape, however, because of their distance.
It is vitally important to understand that the sky looked different at the time of the Pyramids. The overall shape of the Belt Stars has remained remarkably similar although many other parts of the sky have changed dramatically. Thanks to sophisticated computer software it is possible to project the sky back in time, enabling Bauval to verify and build upon his theory.