## Conceptual Physics (12th Edition)

Assuming that the sun's rays are "practically parallel", and referring to Figure 1.1 on page 4, one may form two similar triangles. $$\frac{Pillar \,shadow}{Pillar \,height} = \frac{Distance \,from \,Alexandria \,to \,Syene}{Earth's \,radius}$$ The two 1-to-8 ratios are equal.