Question

explain the cause behind Advance sunrise and delayed sunset.

Answer 1

Heya mate !!!
I can answer that.....

The sun during sunrise is actually a bit lower from horizon but it's rays due to straight transmissited waves reaches us a slightly bent ( it bents becoz of refraction done by the layers of atmosphere ) which results in advance sunrise.
same phenomenon takes place during sunset but the sun rays appears till a late becoz of bent rays. This is called Delayed sunset.
the gap interval is about of 2 mins.

Answer 2

The sun is visible about 2 minutes before the actual su rise and about 2 minutes after the actual sunset because of atmospheric refraction.The density of the air in the atmosphere is not the same everywhere. At some places ,it is higher and in some places it is less.The higher the density ,the greater is the refractive index of air. At sunrise or at sunset , the sun is either at the horizon or below the horizon. Hence, the light Ray's from the sun has to travel a larger distance through the atmosphere. As the rays travel form rarer to denser medium , they start refraction more and more towards the normal. Hence there is a change In the altitude of the sun and they appear at a higher position than they actually are. The sun is visible to us about 2 minutes before actual sunrise and 2 minutes after sunset due to atmospheric refraction. The apparent flattening of the suns disc at sunrise and sunset is also due to the same phenomenon.