It is common practice nowadays for Shuls to publish the zmanim (times) to begin Shabbos (the Sabbath) and other activities. These times, it would seem, are based upon standard calculations of sunrise and sunset for the area in question.
It would seem to me that while these calculations are accurate from a general scientific perspective, the individual point of view would vary based upon the topography of the neighborhood and the horizon.
If one is located behind a mountain, what time is Shkiya or Tzeis?
- Is it when the sun sets below the "calculated" horizon (when the sun should set had the mountain not been there)?
- Is it when the sun sets behind the mountain?
What if one is on top of a mountain? Is Shkiya/Tzeis affected the same way?
What if one is on top of a building, is Shkiya when the sun sets for him or when it sets for people on ground level?
Are such discrepancies between sunset from one's personal vantage point and that of astronomical calculations halachicly significant when calculating when to begin (or end) Shabbos and Yomim Tovim (etc.)?
PLEASE BRING SOURCES