Time discrepancy of a few minutes compared to Chabad.org (version 5.9.9, same location: Brooklyn)

[franckitho]

Hello,

I’ve noticed a small discrepancy of a few minutes between the times returned by hebcal (v5.9.9) and those displayed on Chabad.org for the same date and the same geographical location (Brooklyn, NY).

Both sources are using identical coordinates and timezone settings, yet the results are consistently off by a few minutes.

Date: December 9th 2025

Place = (chabag.org) zip : 11208 (hebcal) lat: 40.669971 lng: -73.860789

Hebcal

{
   "dawn":{
      "functionName":"alotHaShachar",
      "time":"5:39 AM"
   },
   "tallit":{
      "functionName":"misheyakirMachmir",
      "time":"6:12 AM"
   },
   "sunrise":{
      "functionName":"neitzHaChama",
      "time":"7:07 AM"
   },
   "shemaGRA":{
      "functionName":"sofZmanShma",
      "time":"9:27 AM"
   },
   "shacharitGRA":{
      "functionName":"sofZmanTfilla",
      "time":"10:14 AM"
   },
   "midday_night":{
      "functionName":"chatzot",
      "time":"11:47 AM"
   },
   "eMincha":{
      "functionName":"chatzot_plus_30",
      "time":"12:17 PM"
   },
   "mincha":{
      "functionName":"minchaKetana",
      "time":"2:31 PM"
   },
   "plag":{
      "functionName":"plagHaMincha",
      "time":"3:29 PM"
   },
   "sunset":{
      "functionName":"shkiah",
      "time":"4:28 PM"
   },
   "night":{
      "functionName":"tzeit(7.083)",
      "time":"5:05 PM"
   }
}

Chabad.org

{
  "Title": "Dawn (Alot Hashachar)",
  "Link": "/library/article.asp?AID=134527#alot",
  "OpinionInformation": "Alter Rebbe (Default)",
  "ZmanType": "AlosHashachar",
  "Zman": "5:35 AM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765258500000)/",
  "InfoMessage": null
},
{
  "Title": "Earliest Tallit and Tefillin (Misheyakir)",
  "Link": "/library/article.asp?AID=134527#tallit",
  "OpinionInformation": "Beis Baruch, Birur Halocho (Default)",
  "ZmanType": "EarliestTefillin",
  "Zman": "6:13 AM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765260780000)/",
  "InfoMessage": null
},
{
  "Title": "Sunrise (Hanetz Hachamah)",
  "Link": "/library/article.asp?AID=134527#hanetz",
  "OpinionInformation": "Sunrise at sea level",
  "ZmanType": "NetzHachamah",
  "Zman": "7:08 AM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765264080000)/",
  "InfoMessage": null
},
{
  "Title": "Latest Shema",
  "Link": "/library/article.asp?AID=134527#shema",
  "OpinionInformation": "Alter Rebbe (Default)",
  "ZmanType": "LatestShema",
  "Zman": "9:25 AM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765272300000)/",
  "InfoMessage": null
},
{
  "Title": "Latest Shacharit",
  "Link": "/library/article.asp?AID=134527#tefillah",
  "OpinionInformation": "Alter Rebbe (Default)",
  "ZmanType": "LatestTefillah",
  "Zman": "10:13 AM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765275180000)/",
  "InfoMessage": null
},
{
  "Title": "Midday (Chatzot Hayom)",
  "Link": "/library/article.asp?AID=134527#chatzos",
  "OpinionInformation": "Midday (Chatzot Hayom)",
  "ZmanType": "Chatzos",
  "Zman": "11:47 AM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765280820000)/",
  "InfoMessage": null
},
{
  "Title": "Earliest Mincha (Mincha Gedolah)",
  "Link": "/library/article.asp?AID=134527#minchag",
  "OpinionInformation": "Alter Rebbe (Default)",
  "ZmanType": "MinchahGedolah",
  "Zman": "12:12 PM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765282320000)/",
  "InfoMessage": "When a halachic day is less than 12 hours, some wait a full 30 minutes after Chatzot. Earliest Mincha would be 12:17 PM"
},
{
  "Title": "Mincha Ketanah (“Small Mincha”)",
  "Link": "/library/article.asp?AID=134527#minchak",
  "OpinionInformation": "Alter Rebbe (Default)",
  "ZmanType": "MinchahKetanah",
  "Zman": "2:34 PM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765290840000)/",
  "InfoMessage": null
},
{
  "Title": "Plag Hamincha (“Half of Mincha”)",
  "Link": "/library/article.asp?AID=134527#pmincha",
  "OpinionInformation": "Alter Rebbe (Default)",
  "ZmanType": "PlagHaminchah",
  "Zman": "3:34 PM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765294440000)/",
  "InfoMessage": null
},
{
  "Title": "Sunset (Shkiah)",
  "Link": "/library/article.asp?AID=134527#shkiah",
  "OpinionInformation": "Sunset at sea level",
  "ZmanType": "Shkiah",
  "Zman": "4:28 PM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765297680000)/",
  "InfoMessage": null
},
{
  "Title": "Nightfall (Tzeit Hakochavim)",
  "Link": "/library/article.asp?AID=134527#tzeit",
  "OpinionInformation": "Alter Rebbe (Default)",
  "ZmanType": "Tzeis",
  "Zman": "4:59 PM",
  "GmtDate": "/Date(1765238400000)/",
  "GmtDateTime": "/Date(1765299540000)/",
  "InfoMessage": null
}

Event	Hebcal Time	Chabad.org Time	Difference
Dawn (Alos Hashachar)	5:39 AM	5:35 AM	+4 minutes
Tallit (Earliest Tefillin)	6:12 AM	6:13 AM	-1 minutes
Sunrise (Netz Hachamah)	7:07 AM	7:08 AM	-1 minutes
Shema GRA (Latest Shema)	9:27 AM	9:25 AM	+2 minutes
Shacharit GRA (Latest Tefillah)	10:14 AM	10:13 AM	+1 minutes
Midday/Night (Chatzos)	11:47 AM	11:47 AM	+0 minutes
eMincha (Minchah Gedolah)	12:17 PM	12:12 PM	+5 minutes
Mincha (Minchah Ketanah)	2:31 PM	2:34 PM	-3 minutes
Plag (Plag Haminchah)	3:29 PM	3:34 PM	-5 minutes
Sunset (Shkiah)	4:28 PM	4:28 PM	+0 minutes
Night (Tzeis)	5:05 PM	4:59 PM	+6 minutes

Could you please clarify the reason for this difference?

Thx !

[mjradwin]

Differences of 1-2 minutes between Hebcal and other sources publishing candle lighting times or sunset times are expected. Remember that candle lighting times can only be approximated based on location.

Here are a few common reasons why you may see differences in candle lighting times:

https://www.hebcal.com/home/94/how-accurate-are-candle-lighting-times

[franckitho]

Thanks for the clarification and the link.

However, I’ve noticed that some of the differences go beyond the expected 1–2 minutes.
For example, for Minchah Gedolah, Hebcal gives 12:17 PM, while Chabad.org shows 12:12 PM — that’s a 5-minute difference at the same location (Brooklyn, NY).
Similarly, for Tzeis (nightfall), Hebcal shows 5:05 PM, while Chabad.org lists 4:59 PM, which is a 6-minute difference.

[mjradwin]

Oh, right, the issue here is that Chabad.org uses zmanim according to the Baal Hatanya, which we don't yet support. More details are discussed here:

https://hebcal.userecho.com/communities/1/topics/1552-please-add-zmanim-according-to-the-baal-hatanya

We have been waiting (perhaps too long) for a proposed upstream change to enable this

BehindTheMath/KosherZmanim#31

For example, for Minchah Gedolah, Chabad.org uses a different algorithm described here:

https://kosherjava.com/zmanim/docs/api/com/kosherjava/zmanim/ComplexZmanimCalendar.html#getMinchaGedolaBaalHatanya()

The tzeit(7.083) that you are using seems logical to us; this is a commonly-used value for solar depression for tzeis. It must be the case that Chabad.org uses a different solar depression. Can you find out what value they use? This one you can control on your own once you find out from them what solar depression they actually use.

I'm quite sorry we can't yet support parity with the Chabad.org zmanim just yet

[franckitho]

Thank you for all the details and your assistance, the information is both helpful and interesting.

I’ll check and find out what solar depression value Chabad.org uses

[franckitho]

From chabad.org

Tzeit Hakochavim - Nightfall:
The point when 3 medium stars are observable in the night time sky with the naked eye.

This time is the beginning of night for all mitzvahs, including the Torah obligation of reading the evening Shema, counting the Omer, the end of fast days (except for Yom Kippur) and matters relating to the laws of Family Purity. It the preferred time to begin praying Maariv. A baby boy born after tzeit will have his circumcision exactly 8 days later, even if that day is Shabbat. Consult a rabbinic authority for details. The time to end Shabbat and Yom Tov is addressed below.

An average of 3 stars I think the value is 7.083. I’ll check to find out the exact value. Thanks again.