Among the Twenty-eight Constellations in ancient Chinese astronomy, Zi and Shen are the two that are closest to each other (the stars φ1 and δ of Orion are the reference stars, respectively). However, since the late thirteenth century, the traditional order of Zi preceding Shen was inverted due to the influence of precession. This phenomenon was first accurately measured by astronomers employing Western methods during the late Ming Dynasty.