Zmanim Calculations

We generally follow chabad.org zmanim standards.

The time for end of Shabbat and Yom Tov is shown according to the Alter Rebbe. On weekdays, however, we use the universal standard for nightfall of three medium stars, also known as the GR"A (Vilna Gaon). The Zmanim page will list both times on Shabbat and Yom Tov.

The one addition is Tzait Hakochavim per Rabbeinu Tam (72 minutes after sunset), which is not part of the standard Chabad set but is included for those who observe it.

Technical

The halachic calculation library powering this site is written in Java and is open source on GitHub. A companion C library for the Hebrew calendar arithmetic is also available on GitHub.

Sun times are computed without elevation adjustment, which is the standard approach for halachic purposes. The underlying API does accept an elevation value for those who know what they are doing.

Location search and geocoding use the Google Places API.

Links

• Zmanim calculation details — chabad.org
• NOAA Solar Calculation details — gml.noaa.gov
• An authoritative zmanim calculator that supports various halakhic opinions — myzmanim.com
• A Scala library for Jewish calendar calculations — opentorah
• My GitHub
• Rambam: Laws of Sanctification of the New Month — sefaria.org
• Rabbeinu Asher's rules of determining the months and Torah readings — Tur Orach Chaim 428 — sefaria.org  |  traditional print edition — hebrewbooks.org

Contact

Questions or feedback? Email support@hebrewcalendar.net.