How Much Earlier is Sunrise on Mount Everest Due to Elevation?
The greatest sunrise and sunset elevation effect on Earth is on Mount Everest (at 27.988056 N, 86.925278 E as seen on the Direction to Yerushalayim Map). With an elevation of 8,848 Meters (29, 029 feet), sunrise would be up to 15 minutes and 31 seconds earlier on Mount Everest than on sea level. The range of the effect is from 15 minutes and 31 seconds on June 22nd, to a “low” of 13 minutes 41 seconds earlier on March 18th. Being in a large mountain range with obstructed horizons, it is likely never actually seen that early. In addition to questions about mountains, every few months I get asked about how much earlier sunrise/set can be seen in skyscrapers. There are various halacha questions as to whether this actually affects zmanim that I will mention later. Here are some raw numbers. Burj Khalifa (at 25.197222 N, 55.274056 E as seen on the Direction to Yerushalayim Map) is the tallest building in the world. With a height of 828 m (2,717 ft), visible sunrise to someone standing on top of the crown (something unrealistic) on June 22nd would be at 5:24:56 AM versus 5:29:31 AM on sea level, a difference of 4 minutes and 35 seconds. Sunset would be 7:16:35 PM versus 7:12:00 PM at sea level, a difference of 4 minutes and 35 seconds. A more realistic scenario would be the visibility sunrise on the highest floor (the 160th) , an elevation of 672 m at 5:25:23 AM, a difference of 4 minutes and 8 seconds earlier than sea level. Sunset on the 160th floor would be 7:16:08 PM, or 4 minutes and 8 seconds later than at sea level. As far as the halacha being affected by the elevation of buildings, the Baal Hatanya seems to indicate that tall buildings would make sunset later. See Yisroel vehazmanim ישראל והזמנים Vol II, page 910. In the Shraga Lachaim שרגא לחיים footnotes Rabbi Harfenes states that
ויש להוסיף שהוא דבר תמוה לומר דעד שלא נבנו הבנינים הגבוהים היה זמן שבת התלוי בשקעה”ח (שקיעה ראשונה להגאנים ושקיעה שניה לר”ת) מוקדם, ולאחר שנבנו יש לאחר הזמנים, ועד עכשיו שהיו בניו יארק הבנינים התאומויות (טווין-טאוע”ר בלע”ז) שכל א’ מהם היה בת ק”י קומות היה זמן השקיעה מאוחר, ועתה לאחר שהפילו והרסו אותם רשעים וזדים ארורים ימ”ש חזר הדבר לקדמותו להקדים זמן השקיעה.
I have received a few emails over the past year or so about the use of elevation as part of the calculation of various zmanim in the API. All releases of the zmanim API up to the current 1.1 release, use elevation to affect the calculation of all sunrise/sunset based zmanim. While my footnote on the Zmanim Calendar Generator page stated that this only impacted sunrise and sunset (quoting the Yisrael Vehazmanim and Calendrical Calculations), in practice all zmanim calculated based on sunrise and sunset were affected by elevation. An example of a zman that used elevation in 1.1, but will no longer in 1.2, is the calculation of Sof Zman Krias Shema according to the GR”A. The soon to be released version 1.2 limits the impact of elevation to sunrise and sunset only. The Zmanim Calendar Generator page already uses the latest changes to the code. To facilitate changes by ports of the API, a list of changes to the source code of the ZmanimCalendar.java and ComplexZmanimCalendar.java is available in a diff file (a proper unix diff/patch file will not be available at this time). The diff files were generated prior to updating the JavaDocs to simplify the work of anyone modifying ports of the Zmanim API. Detailed sources for not using elevation for anything besides sunrise and sunset can be found in פרק ב׳ סעיף ט׳ (pages 186-187) in the second edition of Zmanim Kehilchasam זמנים כהלכתם by Rabbi Dovid Yehuda Bursztyn.
Update: Elevation Optionally Available as a Factor in Most Zmanim