Calculation of Zmanim
The zmanim here were adapted from the calculations in the excellent PalmOS program,
from Penticon. The following discussion is based on the
zmanim.txt file from that program.
The halacha involved in determining zmanim is quite complicated and there are many different opinions regarding these calculations. Luach is by no means a halachic authority on this subject, and if there is ever any doubt, you should consult the rabbi.
- Halachic Times by Rabbi Yehuda (Leo) Levi
- Astronomical Algorithms by Jean Meeus
- Zmanei HaHalacha L'Maaseh (Hebrew) by Yedidiyah Manat
- The original, open-source Hebcal by Danny Sadinoff
- Hebrew Calendar for Windows by Joe Kohn, the Calendar Maven
- Kaluach by Yisrael (Russ) Hersch
- Ephemeris Tool 2.2 by Manfred Dings
The accuracy of the Zmanim calculations cannot be completely validated. The current tests indicate an accuracy within plus/minus one minute when compared to other Jewish Calendar and Sunrise/Sunset programs. If there is ever a question as to the accuracy of Zmanim calculations, consult the rabbi.
Official sunrise is when the sun just touches the horizon,
and the center of the sun is 50/60 of a degree below the horizon
(for the interested,
the apparent diameter of the sun is 32 arc-minutes, so the center is 16 minutes from
the top, and refraction pulls the image up another 34 minutes.
In all, 50 arc-minutes or 50/60 degrees).
In PHP, this would be
date_sunrise (timestamp, format, latitude , longitude,
90+50/60, gmt_offset). Official sunrise is when the last of the sun
drops below the horizon, and the center of the sun is 50/60 of a degree below the horizon.
In PHP, this is
date_sunset (timestamp, format, latitude , longitude, 90+50/60, gmt_offset).
In the following notes,
sunrise(x) is short for
date_sunrise (timestamp, SUNFUNCS_RET_DOUBLE, latitude , longitude,
sunset(x) is short for
date_sunset (timestamp, SUNFUNCS_RET_DOUBLE, latitude , longitude,
90+x, gmt_offset); i.e. the top of sun is x degrees below
the horizon and the functions return hours from midnight.
|Sha'a Zmanis/Sha'a Zmanit||1/12 of the time between Sunrise and Sunset||
|Alos HaShachar/Alot HaShachar||According to the Rambam, when the sun is 16.1 degrees below the horizon||
|Earliest Tallis/Tallit||The earliest time for putting on Tallis/Tallit and Tefillin. The common value used is when the sun is 11 degrees below the horizon||
|Latest Sh'ma||The latest time that Sh'ma may be recited according to the GR"O; 3 sha'os zmanios/sha'ot zmaniot from netz||
|Hatzos/Hatzot Hayom||Midday; halfway between sunrise and sunset||
|Mincha Gedola||This is the earliest that Mincha may be recited. This is half an hour after hatzos/hatzot hayom, with an "hour" defined as the larger of a clock hour and a sha'a zmanis/sha'a zmanit||
|Plag Hamincha||1.25 sha'os zmanios/sha'ot zmaniot before sunset||
|Tzeis/Tzeit HaKochavim||There are many standards for "3 small stars visible". More stringent standards include when the sun is 6 or 8.5 degrees below the horizon. Rabbi Bienenfeld has paskened that Young Israel uses the standard of 42 minutes after sunset||
|Light Candles||18 minutes before sunset||