Generalized Planispheres for Archaeoastronomical Research

School of Informatics, Walailak University, Thailand

Archaeoastronomy is an important approach in studying archaeology since every human civilisation integrate astronomical knowledge in several aspects of their lives. Although planetarium software is widespread among astronomers, the planisphere still serves as an essential instrument to archaeoastronomers whose agility is crucial in fieldwork. However, the spatiotemporal domain of the typical planisphere used by astronomers is currently limited to a few degrees of latitude and a few decades of time. These limits prevent archaeoastronomers from using the traditional planisphere as archaeological studies often cover a large area with a time span of more than a century. This study successfully overcomes these limits by generalizing the traditional planisphere into a pair of planispheres that convert between (A) Ecliptic and Equatorial coordinate systems and (B) Equatorial and Horizontal coordinate systems. Planisphere (A) solves the temporal limit by simulating the Earth's axial precession (i.e., the phenomenon that causes the change of position of the North Star or Polaris over time), which extends the temporal domain from less than ±100 years to over ±10,000 years. It was also designed with the knowledge of ancient Indian astronomy to make it suitable for studying ancient Thai astronomy at any year of interest. Planisphere (B) solves the spatial limit by modifying the traditional planisphere to be unable to yield azimuth and altitude of a celestial object but its azimuth and local time of rising and setting at any latitudes on the Earth. Although this study cannot combine both planispheres into a single instrument, they can provide the shortcut in testing many hypotheses relating to archaeoastronomy to complement modern-day planetarium software.