Which geometrical principle did medieval Islamic astronomers employ using astrolabes to determine qibla direction?

💡 Explanation

When determining the qibla, Islamic astronomers projected the 3D celestial sphere onto the 2D surface of the astrolabe using stereographic projection to simplify angular calculations, because it preserves angles but not areas. Therefore stereographic projection is the core principle, rather than harmonics, ellipse mapping, or coordinate transformations; these lack direct mapping to the astrolabe's design.

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