Thursday, August 31, 2017

time - Precise Zemanim?



This site (see the paragraph starting with "accuracy") says that no one can predict the times for sunrise and sunset to within a minute accurately for a given location because of certain atmospheric fluctuations. If so, how do some people predict zemanim (times of day with halachik significance) to a number of seconds, or even the end of shabbat to within a minute? Also, I have been to hanetz minyanim who are very careful to start at the moment of sunrise. But according to this, that's impossible to predict!


I suppose my question is really just looking for some justification for the common practice. Do any rabbis discuss this phenomenon? Do they say if it matters or not?


Note: I know most zemanim services will say "Please don't rely on this till this last moment; these may not be exact" but that sounds more like a legal disclaimer than a statement of fact.




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