What is the effect of absence of atmospheric refraction on sin rise and sunset time? Is it will be delayed or earlier for sunrise and sunset, and why? Thank you:)
The simple answer is that atmospheric refraction makes the disk of the sun visible at sunrise or sunset, when it's actually half a degree or so below the horizon:
In reality, both the extent of refraction of the sun's disk and the refraction of the apparent horizon come into play. Both depend on the atmosphere's density and temperature profile; which changes irregularly. That makes it impossible to predict exact sunrise or sunset times when there is an atmosphere.