The Zmanim Project uses sea level by default to calculate sunrise and sunset. They rationalise this by referencing a machloket on the subject.

I don't have access to the sefer זמנים כהלכתם, otherwise I would simply look up the reasoning there. On my own I simply can't comprehend why you should disregard the time that an observer, wherever they might be, actually sees the sun coming up or going down the horizon. In Johannesburg it makes a different of up to 6½ minutes.

Can anyone read up what Rabbi Dovid Yehudah Bursztyn writes there, or otherwise explain his logic?

  • 1
    The sky above you doesn't know your altitude and darkens anyway. Hence waiting X minutes after observed sunset doesn't make any sense. (Though this line of questioning may just be another reason to discount the whole notion of solar-disk sunset)
    – Double AA
    Aug 12, 2022 at 8:01
  • According to the Alter Rebbe, hanetz amiti, true (halachic) sunrise, is when the top of the sun’s disk is visible at an elevation similar to the mountains of Eretz Yisrael. (see: chabad.org/library/article_cdo/aid/3209349/jewish/…)
    – Shmuel
    Aug 12, 2022 at 8:23
  • 1
    See also this discussion citing Rav Moshe Feinstein: judaism.stackexchange.com/a/15435/27180
    – Shmuel
    Aug 12, 2022 at 8:24

1 Answer 1


A correction is necessary - the זמנים כהלכתם explicitly writed that only for צאת הכוכבים does elevation not matter.

The explanation given is that צאת הכוכבים is determined by the darkness of the upper firmament (רקיע העליון) which is not affected by the elevation of an observer.

In his words

משום דזמן היראותם של הכוכבים תלוי רק בדרגת החשכה של פני הרקיע העליון (דהיינו כיפת הרקיע, לאפוקי מהרקיע שבאופק), והתרחבות אופק-הראייה לעומד על ההר גורמת רק להארת קו האופק למשך זמן רב יותר (וכן להיפך בעמק) ולא גורמת כלל לשינוי בהארת פני רקיע העליון

  • Do you mean to say that the Zmanim Project have read the sefer incorrectly? They seem pretty definite about their interpretation: " According to Rabbi Dovid Yehudah Bursztyn in his Zmanim Kehilchasam, 7th edition chapter 2, section 7 (pages 181-182) and section 9 (pages 186-187), no zmanim besides sunrise and sunset should use elevation. " Aug 13, 2022 at 18:21
  • Perhaps you are using a different edition of the sefer? Aug 13, 2022 at 18:59
  • @MichaelSandler The name of the chapter reads "זמן "צאת הכוכבים שוה על ההר ובעמק ובמישור . The first paragraph starts כבר כתבו רבים דלענין צאת הכוכבים המציאות.... I am using the 3rd edition, but I am assuming that no change was made of such magnitude.
    – Yoreinu
    Aug 14, 2022 at 2:53

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