Eliezer asks:
Given the nature of the refraction of light, and the approximate 8 minutes it takes for light to reach Earth from the sun, how do we determine the true moment of the rise or set of the disc of the sun over the horizon.
Eliezer,
The Kollel replies:
That is an interesting point, Eliezer.
The answer to your question is that as with all of the Torah, the laws regarding sunrise and sunset were given to be put into practice by humans. Thus, they are determined by human observatn, not by computational techniques. Any computational techniques used to determine sunrise and sunset will have to calculate the moment that we Jews are able to experience with our eyes as the time of the rising and setting of the sun.
Best regards,
Mordecai Kornfeld