Patterns in Time Halachic Hours
Parsha Pages Youth | February 06, 2025
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Patterns in Time Halachic Hours

Parsha Pages Youth | June 27, 2025

PATTERNS IN TIME

Halachic Hours

Halachic hours are not fixed hours as the standard accepted 24 hours of the day. The halachic hour generally represents one-twelfth of the day or night and is called one sha'ah zemanit — varying in length with the seasons. However, every day has twelve such hours and every night has 12 such hours.

For example, in a day (from sunrise to sunset) that is 12 standard hours long, each halachic hour would be 60 minutes. However, when there are 13 standard hours between sunrise and sunset, each halachic hour would correspond to 65 minutes (60*13/12, or 780/12), and so on.

There are two major opinions of the means to define the day:

  • Shitas haGra —the Gaon of Vilna (or the Alter Rebbe, the first Rebbe of Lubavitch) calculate the hour as one-twelfth of the time from sunrise to sunset
  • Mogan Avrohom - one-twelfth of the time from dawn (itself variously defined) to dusk/nightfall

Obviously an hour calculated according to the second system will be longer than that of the first. However, given that the calculation of the latter begins at an earlier point in time (dawn rather than sunrise), the end of three hours, for example according to that calculation, will occur earlier than it does according to the shitas haGra.

SAMPLE (for Los Angeles, California)

12/21/2007
Standard time03/21/2008
Daylight savings06/21/2008
Daylight savingsDawn (day begins - Mogan Avrohom)05:34 a.m.05:40 a.m.04:10 a.m.Sunrise (beginning of day to Shitas HaGra)06:54 a.m.06:54 a.m.05:42 a.m.Midday (Chatzos)11:51 a.m.1:00 p.m.12:55 p.m.Sunset (end of day to Shitas HaGra)04:48 p.m.07:06 p.m.08:08 p.m.End of Dusk (end of day - Mogan Avrohom)06:08 p.m.08:20 p.m.09:39 p.m.

Based on the above sample, complete the following chart

12/21/2007
Standard time03/21/2008
Daylight savings06/21/2008
Daylight savingsLength of Halachic hour:
to Gra
To Mogan Avrohom49.5 minutes
1 hour 2 min.1 hour 1 minute
1 hour 13 min.1 hour 12 minutes
1 hour 27.5 min.End time for Krias Shema (end of third hour):
to Gra
To Mogan Avrohom9:41 a.m.
8:40 a.m.9:57 a.m.
9:19 a.m.9:18 a.m.
8:32 a.m.End time for Sharcharis (end of fourth hour):
to Gra
To Mogan Avrohom10:32 a.m.
9:42 a.m.10:58 a.m.
10:32 a.m.10:30 a.m.
9:59 a.m.Middle of Night to all11:51 p.m.1:00 a.m.12:55 a.m.

SEE WWW.MYZMANIM.COM
http://hebrewcalendar.net/htdocs/zmanimhelp.en.html
http://www.aishdas.org/toratemet/en_times.html

OBJECTIVE: FAMILIARITY WITH THE PATTERNS OF TIME IN JEWISH LAW
AGE GUIDE: TWELVE YEARS OLD AND OLDER (THROUGH ADULT)

PATTERNS IN TIME

Halachic Hours

Halachic hours are not fixed hours as the standard accepted 24 hours of the day. The halachic hour generally represents one-twelfth of the day or night and is called one sha'ah zemanit — varying in length with the seasons. However, every day has twelve such hours and every night has 12 such hours.

For example, in a day (from sunrise to sunset) that is 12 standard hours long, each halachic hour would be 60 minutes. However, when there are 13 standard hours between sunrise and sunset, each halachic hour would correspond to 65 minutes (60*13/12, or 780/12), and so on.

There are two major opinions of the means to define the day:

  • Shitas haGra —the Gaon of Vilna (or the Alter Rebbe, the first Rebbe of Lubavitch) calculate the hour as one-twelfth of the time from sunrise to sunset
  • Mogan Avrohom - one-twelfth of the time from dawn (itself variously defined) to dusk/nightfall

Obviously an hour calculated according to the second system will be longer than that of the first. However, given that the calculation of the latter begins at an earlier point in time (dawn rather than sunrise), the end of three hours, for example according to that calculation, will occur earlier than it does according to the shitas haGra.

SAMPLE (for Los Angeles, California)

12/21/2007
Standard time03/21/2008
Daylight savings06/21/2008
Daylight savingsDawn (day begins - Mogan Avrohom)05:34 a.m.05:40 a.m.04:10 a.m.Sunrise (beginning of day to Shitas HaGra)06:54 a.m.06:54 a.m.05:42 a.m.Midday (Chatzos)11:51 a.m.1:00 p.m.12:55 p.m.Sunset (end of day to Shitas HaGra)04:48 p.m.07:06 p.m.08:08 p.m.End of Dusk (end of day - Mogan Avrohom)06:08 p.m.08:20 p.m.09:39 p.m.

Based on the above sample, complete the following chart

12/21/2007
Standard time03/21/2008
Daylight savings06/21/2008
Daylight savingsLength of Halachic hour:
to Gra
To Mogan Avrohom49.5 minutes
1 hour 2 min.1 hour 1 minute
1 hour 13 min.1 hour 12 minutes
1 hour 27.5 min.End time for Krias Shema (end of third hour):
to Gra
To Mogan Avrohom9:41 a.m.
8:40 a.m.9:57 a.m.
9:19 a.m.9:18 a.m.
8:32 a.m.End time for Sharcharis (end of fourth hour):
to Gra
To Mogan Avrohom10:32 a.m.
9:42 a.m.10:58 a.m.
10:32 a.m.10:30 a.m.
9:59 a.m.Middle of Night to all11:51 p.m.1:00 a.m.12:55 a.m.

SEE WWW.MYZMANIM.COM
http://hebrewcalendar.net/htdocs/zmanimhelp.en.html
http://www.aishdas.org/toratemet/en_times.html

OBJECTIVE: FAMILIARITY WITH THE PATTERNS OF TIME IN JEWISH LAW
AGE GUIDE: TWELVE YEARS OLD AND OLDER (THROUGH ADULT)

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Parsha Pages Youth | February 06, 2025