No you're right! In all the methods to calculate or draw sundials, geometric or analytic, the Sun is always considered punctiform, and reduced to its center, and no account is taken of refraction, of the lowering of the horizon (horizon dip), of other astronomical phenomena such as parallax, etc.. Sunset and sunrise (for the calculation of temporary or italic hours) are always the instants when the center of the Sun crosses the theoretical horizon. Even Islamic astronomers, who well knew the phenomenon of refraction, do not take into account of it in the calculation of sundials and of the prayers lines.
Best Gianni Ferrari
--------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
