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What is the time difference between the actual sunset and apparent sunset ?
Explanation
The time difference between the actual sunset and the apparent sunset is about two minutes. This phenomenon is caused by atmospheric refraction.
As sunlight enters the Earth's atmosphere, it passes through layers of air with varying densities and refractive indices. The light rays bend (refract) towards the normal as they move from rarer to denser layers. Due to this continuous bending, the sun appears to be slightly higher in the sky than its actual position. Consequently, the sun remains visible to an observer for about two minutes after it has physically crossed below the horizon (actual sunset).
The same effect occurs at sunrise, where the sun is visible about two minutes before it actually rises. Therefore, atmospheric refraction extends the duration of daylight by approximately four minutes in total.