Question

Why is day longer by four minute?

Answer 1

The sun is seen about 2 minutes before the actual sunrise and 2minutes after the actual sunset because of atmospheric refraction. so the time from Sunrise to Sunset is lengthened by 2+2=4 minutes because of atmospheric refraction.

Answer 2

During sunrise, the light rays bend due to our atmosphere and we see the sun early even though the sun is just below the horizon. Similarly, at sunset, due to the same bending of light rays, we see the apparent position of the sun, not the actual position.

To sum up, due to refraction we see the sun rise about two minutes before it’s actually there and during sunset we see it for around two minutes more, even though it has already moved from that position. And our day exceeds by 4 minutes.