By default we follow chabad.org1 zmanim standards. That is, we follow the Alter Rebbe (aka Baal HaTanya) for times of day unless you choose otherwise.
The time for end of Shabbat and Yom Tov is shown according to the time for 3 small stars. On weekdays, however, we use the universal standard for nightfall of three medium stars. The Zmanim page will list both times on Shabbat and Yom Tov. Note that the later time must be observed for activities that are forbidden on Shabbat. See below for the methodology details.
The Zmanim page lets you specify which halachic opinion to use for calculating the daytime hours (sha'ah zmanit). This choice affects most daytime zmanim: latest time for Shema, latest time for Shacharit, Mincha Gedola, Mincha Ketana, and Plag HaMincha. Three general opinions are available:
Alter Rebbe (default) — Follows R' Shneur Zalman of Liadi in his Siddur2. Halachic hours are measured from the amiti (astronomical) sunrise to amiti sunset — the moment the geometric center of the sun's disk crosses the horizon, ignoring refraction. End of Shabbat is set to when the sky darkens to 8.5° below the horizon. This is the standard for the Chabad community.
GR"A (Vilna Gaon) — Halachic hours are measured from visible sunrise (when the sun's upper edge first appears) to visible sunset. End of Shabbat is set to when three medium-sized stars are visible, approximately 6° below the horizon. This is the majority opinion followed by most Ashkenazi and Sephardi communities. See Biur HaGr"a OC 459:23.
Magen Avraham — Halachic hours are measured from dawn (72 minutes before sunrise, or when the sun is 16.1° below the horizon) to nightfall (72 minutes after sunset). Because the "day" is longer, halachic hours are longer, and every daytime zman falls earlier than with the GR"A. Some communities follow this stringently for Shema. At very high latitudes where the sun never reaches 16.1° below the horizon, halachic hours are computed from halachic midnight instead — see Magen Avraham at high latitudes.
Note: Magen Avraham's version of the 72-minute nightfall is used only for calculating the halachic hour and the parts of the day; it is not used for any other halachic purpose4.
These reference rows are hidden by default and can be turned on in the gear menu:
Times are computed from your geographic location's astronomical events. Angles given below refer to the sun's depression below the horizon.
Visible sunrise (hanetz hachama) — The moment the top of the sun first appears above the horizon: sun's upper edge at −0.833° (accounting for average atmospheric refraction and the sun's semi-diameter).
Visible sunset (shkiat hachama) — Same 0.833° threshold at the end of the day: sun's upper edge disappearing on the western horizon.
Amiti sunrise / amiti sunset (Alter Rebbe) — The astronomical event: the geometric center of the sun's disk at −1.583°, i.e., disregarding refraction and taking the true horizon. This is what the Alter Rebbe treats as sunrise/sunset for the purpose of the halachic day. See Seder Hachnasat Shabbat, Siddur Torah Ohr2.
A halachic hour is one-twelfth of the halachic day. What counts as the "day" depends on the opinion followed:
The point at which the eastern sky begins to lighten. The site supports several opinions:
The point at which one can distinguish the blue thread of the tzitzit from the white. This is the earliest time to put on talit and tefillin.
The end of the third halachic hour from the start of the day (per the selected opinion). See Mishna Berachot 1:212, per the ruling of R' Yehoshua that we follow; Shulchan Aruch HaRav OC 58:313.
The end of the fourth halachic hour. See Berachot 26a14 — up to four hours the tefilla is le-chatchila.
Chatzot hayom (noon) — the midpoint between sunrise and sunset. Chatzot halayla (midnight) — 12 halachic hours after noon, i.e., the midpoint between sunset and the following sunrise.
6.5 halachic hours from the start of the day. The earliest time one may pray Mincha.
9.5 halachic hours from the start of the day. Preferred earliest time for Mincha le-chatchila.
10.75 halachic hours from the start of the day. The earliest time one may accept Shabbat or daven Ma'ariv (per certain opinions).
Visible sunset — the sun's upper edge disappearing on the western horizon (−0.833°). This begins bein hashmashot, the disputed period between day and night.
The end of bein hashmashot — the halachic transition from day to night. Several opinions:
Nightfall with three small stars, 36 minutes at −8.5°. This is the same for all major opinions. See Shulchan Aruch OC 293:215. When the Rabbeinu Tam row is enabled, it appears alongside as a stringent alternative. Rabbeinu Tam nightfall might not be displayed in high latitudes where it occurs before the time of three small stars.
At high enough latitudes (roughly above 50° in the summer/winter extremes) the sun never dips 16.1° below the horizon, so the Magen Avraham dawn does not occur. When this happens, the site sets the halachic hour to two clock hours (equivalent to treating the halachic day as 24 hours long) and reckons all daytime zmanim from halachic midnight. Times computed this way are marked with an asterisk (*) and carry a footnote advising to consult a competent rav before relying on them.
© Isaac Mushinsky, 1998–2026