Concept:The bending of light when it passes through layers of air with different densities is called atmospheric refraction.
This causes the Sun to appear above the horizon even when it is actually below it.
Explanation:Near the Earth’s surface, air layers closer to the ground are denser than those higher up.
At sunrise and sunset, the Sun is just below the horizon.
Light rays from the Sun travel from the vacuum of space into the Earth’s atmosphere.
They pass through successively denser air layers, bending towards the normal each time.
By the time the rays reach an observer on the ground, they appear to come from a point above the horizon.
Thus, the Sun is visible a little before actual sunrise and a little after actual sunset.
This early rise and late set last about 2 minutes each.
The same atmospheric refraction also causes stars to twinkle due to changing air density.
However, the question specifically asks about the Sun’s visibility before sunrise and after sunset.
The correct reason is atmospheric refraction, not total internal reflection, apparent shift, or dispersion.
Answer:B. atmospheric refraction
