Why was the Sun not directly overhead in Alexandria when it was in Syene?

The reason the Sun was not directly overhead in Alexandria when it was directly overhead in Syene is due to the Earth's spherical shape.

As the Earth is a sphere, different locations experience sunlight at varying angles depending on their latitude. Syene, located near the tropic of cancer, will have the Sun directly overhead at noon during specific times of the year, particularly during the summer solstice. However, Alexandria is situated further north and, because of the curvature of the Earth, it will not experience the Sun being overhead at the same time.

This phenomenon is a direct result of the spherical geometry of the Earth, which means that as you move north or south from the equator, the angle at which sunlight hits the surface changes. Therefore, at any given time, locations at different latitudes will experience the position of the Sun differently, correlating with the Earth's shape and rotation.