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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?

  1. Is it when the sun sets below the "calculated" horizon (when the sun should set had the mountain not been there)?
  2. 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

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O.K, I know I'm pushing it with the "local interest" tag, but how often will we really get away with using it. :) –  Yirmeyahu Apr 29 '10 at 5:21
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Within a single community I've never heard of anybody altering the times based on, say, living on a hill. Is that what you're asking about? (Several shuls local to me publish Shabbat times, as do the kosher grocery and the newspaper.) –  Monica Cellio Nov 13 '11 at 5:13
    
Are you asking about Tzeis (per your body) or Haneitz (per your title)? –  Double AA Mar 28 '12 at 5:25
    
@isaac can we just synonym that? there are plenty of questions related to sunset and it seems consensus so far is to put them in with geography. –  Double AA Mar 28 '12 at 5:31
    
@DoubleAA, you can propose synonyms yourself. –  msh210 Mar 28 '12 at 17:08
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4 Answers

This question is discussed by Rav Moshe (OC 1:97)

The upshot is that, by the strict definition of law, sunset goes by when the sun dips below the horizon and is independent of the viewer. So for those on a mountain, halachic sunset would occur earlier that when they see the sun set. For those in a valley, it would be later.

Nightfall is dependent on "seeing" 3 stars, which would be relative to the viewer and would have different times based on how much the sun's light still obscures the view of the stars. Someone situated in a valley would have a different time than one on a plane.

Rav Moshe concludes that based on the ancient practice (chumra) of Teveria vs Tzipori that valley folk should still take in Shabbos when the sun goes below the mountain even though it hasn't set in the plane, and goes further to say that "baalei Torah" should be strict to finish shabbos as late as tseis hakochavim of those on the mountain if the latter town is closeby.

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Based on my Internet roamings on this earlier, there are two elevations: that of the person, and that of the horizon. IOW both being higher/lower myself, and the terrain at the horizon, are factors in the time of the sun's apparent setting. The question regards the horizon, but it sounds like the teshuvah you cite is dealing with the elevation of the person. –  yitznewton Mar 28 '12 at 20:57
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@yitznewton, elevation becomes a factor at tzeis when the person can see 3 stars, which is based on the sun's light (or rather lack thereof). Meikar hadin, shkiah is constant relative to the plane (no mountain/valley). –  YDK Mar 28 '12 at 21:53
    
Not according to the OU pesak in my answer, IIUC –  yitznewton Mar 28 '12 at 23:32
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I see from the OU that both sunset times are given because there is a "difference of opinion" (as opposed to straight Rav Moshe where sea-level horizon is meikar hadin and any differences are chumra.) Sunrise is inconsequential in Yerushalaim re the machlokes. –  YDK Mar 28 '12 at 23:38
    
Note: This was penned as an answer to another question, which was thereafter merged hither. –  msh210 Mar 29 '12 at 6:32
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At least to some, yes, mountains do change what time Shabbos comes in.

From Chabad.org:

"...Palm Springs has special rules with regard to when Shabbat begins. This is due to the large mountain which is directly west of the city. I've been there for Shabbat myself and I can tell you that it does get darker there earlier than cities nearby.

Although "sunset" may be a while later, Shabbat begins based on "visual sunset" not "actual sunset.""

And from the author's comment to that article:

This is definitely the locally accepted halacha and affects all matters which pertain to biblical law. This was the directive of Rabbi Zalman Shimon Dworkin OBM many years ago, based on the ruling of the preeminent halachic authority, Rabbi Schneur Zalman of Liadi.

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So what about taking out Shabbos? Is that early too? –  Desert Star Jul 9 '12 at 15:01
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This is probably not a full answer to your question but is helpful.

MyZmanim.com "Zmanim Accuracy":

Obstructions on the Horizon All times for sunrise and sunset are computed for a flat horizon clear of obstructions. Obstructions on or before the horizon (such as hills and mountains) may delay the appearance of sunrise and/or advance the appearance of sunset. The Gemara and Rishonim do not discuss whether or not such obstructions should affect the times of HaNetz and Shkiah.

Consequences of Elevation Elevation has the effect of delaying the appearance of sunset, and advancing the appearance of sunrise. Yerushalayim, for example, has an approximate elevation of 800 meters above its western horizon. As such, Shkiah occurs several minutes later than it would, had Yerushalayim not been elevated. MyZmanim.com provides both sunrise/sunset in a level region, and sunrise/sunset taking into account elevation.

Unless otherwise indicated, printed sunrise/sunset times are for an observer in a level region.

Note that elevation has consequences only with regard to the times of HaNetz Hachama and Shkiah (and according to some customs, also Tzes Shabbos 72 minutes and candle lighting). Other zmanim times are - according to most Poskim - not affected by elevation.

I conducted an experiment where I altered my elevation from 0 to 30 meters (98 feet). The higher elevation would make Shabbos 67 seconds earlier.

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I would think the higher the elevation the "later" it would start? –  Yirmeyahu Apr 29 '10 at 15:16
    
then why does shabbos start earlier in Yerushalayim? –  Jeremy Apr 29 '10 at 16:04
    
I checked again. The higher elevation makes both sunrise and sunset earlier. –  Tzvi Apr 30 '10 at 1:14
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If I understand this article correctly, the OU uses a sea-level horizon. No source listed except presumably the OU poskim.

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Note: This was penned as an answer to another question, which was thereafter merged hither. –  msh210 Mar 29 '12 at 6:32
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