We see the sun actually 2 minutes before the real sunrise and thats because of atmospheric refraction. We called the sunrise only when the sun actually cross the horizon line, the flattering of sunrays makes us fell the sun is rising and the whole sky is effecting with it when in real the have 2 minutes in hand to actually rise.
The refraction of light through the atmosphere is responsible for many interesting phenomena.For eg:-the sun is visible to us a little before the actual sunrise and until a little after the actual sunset due to refraction of light through the atmosphere. By actual sunrise we mean the actual crossing of the horizon by the sun. 
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