Why is the Sun visible to us about 2 minutes before the actual sunrise and about 2 minutes after the actual sunset?

The phenomenon of the Sun being visible to us about 2 minutes before the actual sunrise and about 2 minutes after the actual sunset is known as atmospheric refraction. Atmospheric refraction occurs because the Earth’s atmosphere acts like a lens, bending or refracting light as it passes through different layers of the atmosphere.

During sunrise and sunset, when the Sun is near the horizon, its light has to pass through a thicker layer of the Earth’s atmosphere compared to when it is directly overhead. The Earth’s atmosphere is composed of air layers with varying densities, and the density decreases with altitude.

As sunlight enters the Earth’s atmosphere at a low angle, it undergoes refraction, bending slightly towards the Earth’s surface. This bending of light causes the Sun to appear slightly above the actual horizon before it has physically crossed it during sunrise and after it has physically set during sunset.

The magnitude of atmospheric refraction varies with atmospheric conditions, but on average, it leads to the Sun being visible for a few minutes before it technically rises and after it officially sets. This effect is more pronounced at higher latitudes and can contribute to the extended twilight periods observed around sunrise and sunset.