Why sun appears oval at sunrise and sunset but appears circular at noon?

At sunrise and sunset

the sun is near the horizon. The rays of light from upper &

lower part of the periphery of the sun bend unequally on travelling

through earth's atmosphere. That is why sun appear oval or

flattened at sunrise and sunset.

At noon sun is

overhead. The rays of light from the sun enter earth's atmosphere

normally. Therefore they suffer no refraction or bending on passing

through.

Hence the sun appears

circular at noon.