Atmospheric Refraction

Atmospheric refraction is the bending of light as it passes through the Earth's atmosphere. It occurs because the atmosphere has varying densities, which causes the speed of light to change. This change in speed causes the light rays to bend or refract.

Why the Sun is seen before it rises and after it sets

The phenomenon of seeing the Sun slightly before it rises and for a short while after it sets is due to atmospheric refraction. Here's an explanation of why this happens:

1. Bending of light at the Earth's atmosphere: When light from the Sun enters the Earth's atmosphere, it encounters different layers of air with varying densities. The light rays are refracted or bent as they pass through these layers.

2. Refraction near the horizon: When the Sun is near the horizon, its light rays have to pass through a larger portion of the Earth's atmosphere compared to when it is directly overhead. This means that the light rays are subjected to more refraction near the horizon.

3. Bending of light towards the observer: The bending of light near the horizon causes the rays to curve slightly towards the observer. As a result, the Sun appears higher in the sky than it actually is. This is known as the apparent shift in the direction of the Sun.

4. Effect on sunrise and sunset: Due to the apparent shift in the direction of the Sun caused by atmospheric refraction, the Sun appears to be above the horizon even before it has physically risen and after it has physically set. This explains why we can still see the Sun for a short while before sunrise and after sunset.

5. Duration of visibility: The duration for which the Sun is visible before sunrise and after sunset varies depending on factors such as the latitude, time of year, and atmospheric conditions. In general, the higher the latitude, the longer the duration of visibility.

In conclusion, the reason we can see the Sun slightly before it rises and for a short while after it sets is due to atmospheric refraction. The bending of light near the horizon causes an apparent shift in the direction of the Sun, making it visible even when it is physically below the horizon.