Abstract
This paper is an attempt to show the astronomical design principles that are encoded in the geometrical forms of the largest five pyramids of the fourth Egyptian dynasty, in Giza and Dahshur plateaus, based on using the pyramids' design-modules that are mentioned in the so-called Rhind Mathematical Papyrus. It shows the astronomical algorithms for quantifying the slopes of pyramids, with reference to specific range of earth's axial tilt, within spherical co-ordinates system. Besides, it decodes the design of the ancient Egyptian cubit rods with reference to the systems of measurement used by Herodotus and Diodorus, and proves that Herodotus never talked about Giza pyramids and he meant only the pyramids of Memphis in Dahshur. In addition, it proves that the Egyptian arrow of 22.5cm, or half the mean cubit of 45cm, is the largest common divider of the design-modules of these pyramids, and accordingly it retrieves their intended astronomical design dimensions.