Question

The sun near the horizon appears flattened at the sun set and sun rise. Explain why.

Answer 1

This is due to atmospheric refraction. The density and refractive index of the atmosphere decreases with altitude. so the rays from top to bottom portion of the sun on horizon are refracted by different degrees. This causes the apparent flattening of the sun. But the rays from the side of the sun on a horizontal plane are generally refracted by the same amount, so the sun will appear circular along the sides.