A perpetual Jewish Calendar

by Danny Sadinoff (portions by Michael J. Radwin)

Hebcal is a program which prints out the days in the Jewish calendar for a given Gregorian year. Hebcal is fairly flexible in terms of which events in the Jewish calendar it displays. Each of the following can be individualy turned on or off:

• The Hebrew date
• Jewish Holidays (including Yom Ha'atzmaut and Yom HaShoah etc.)
• The weekly Sedrah
• The day of the week
• The days of the Omer

usage: hebcal [options] [[ month [ day ]] year | YYYY-MM-DD ]
       hebcal help
       hebcal info
       hebcal cities
       hebcal warranty
       hebcal copying

Hebcal prints out Hebrew calendars one solar year at a time. By specifying month, day, or year, output can be limited to a particular month or date in a particular year.

Note that year is usually a four-digit integer, so 92 is during the Roman period, not the late twentieth century. If the Hebrew dates option (-H) is turned on, this number represents the Jewish calendar year.

month is a number from 1..12, or the name of a Jewish calendar month. day is a number from 1..31.

A single day may also be specified as YYYY-MM-DD (ISO 8601 date format).

For example, the command hebcal 10 1992 will print out the holidays occurring in October of 1992 C.E., while the command hebcal Tish 5752 will print dates of interest in the month of Tishrei in Jewish calendar year 5752.

If no year is specified, hebcal will print to stdout the dates of the Jewish holidays in the current secular year.

For example, hebcal -ho will just print out the days of the omer for the current year.

Hebcal’s candlelighting times are only approximations. If you ever have any doubts about its times, consult your local halachic authority. If you enter geographic coordinates above the arctic circle or antarctic circle, the times are guaranteed to be wrong.

In addition to candle-lighting on Erev Shabbat and Chag, the -c switch also generates Havdalah and fast start/end times.

By default, candle-lighting times are 18 minutes before sunset (see -b option above for exceptions).

Chanukah candle-lighting times are at bein hashmashos (13.5 minutes before a solar depression of 7.083 degrees) on weekdays. Chanukah candles are lit just before Shabbat candles on Friday, and immediately after Havdalah on Saturday night.

Havdalah time defaults to 72 minutes after sunset (Rabbeinu Tam). Adjust with the -m (minutes) option or with -G (havdalah degrees below horizon).

Minor fasts begin in the morning at alot haShachar (solar depression 16.1 degrees) and conclude at tzeit for 3 medium sized stars (solar depression 7.083 degrees). Major fasts (Yom Kippur and Tish'a B'Av) begin just before sunset (at regular candle-lighting time) and conclude at Havdalah time.

Hebcal contains a small database of cities with their associated geographic information and time-zone information. Run hebcal cities to print a list of cities supported by the -C city flag.

If your city is NOT on the list, then in order to customize hebcal to your city, you will need to pass it the latitude, longitude, and timezone (see the manual).

Suppose you live in Oshkosh, Wisconsin. Your latitude is 44.0181, and your longitude is -88.6353. You are in timezone America/Chicago. We'll round the geographic coordinates to the nearest minute.

In order to get candlelighting times for the current year, you would type

hebcal -ch --geo 44.0181,-88.6353 -z America/Chicago

The geographic and time information necessary to calculate sundown times can come to hebcal any of three ways:

1. The default: the system manager sets a default city ("New York") when the program is compiled.
2. Hebcal looks in the environment variable HEBCAL_CITY for the name of a city in hebcal’s database, and if it finds one, hebcal will make that the new default city.
3. 1 and 2 may be overridden by command line arguments, including those specified in the HEBCAL_OPTS environment variable. The most natural way to do this is to use the −C city command. This will localize hebcal to city. A list of the cities hebcal knows about can be obtained by typing hebcal cities at the command prompt. If the city you want isn’t on that list, you can directly control hebcal’s geographic information with the --geo (or −l and −L) and −z switches.

For a status report on customizations, type hebcal info at the command prompt.

Hebcal uses two environment variables:

HEBCAL_CITY

Hebcal uses this value as the default city for sunset calculations. A list of available cities is available with from hebcal with the command: hebcal cities

HEBCAL_OPTS

The value of this variable is automatically processed as if it were typed at the command line before any other actual command-line arguments.

Every time hebcal is run, it checks this variable. If it is non-empty, the arguments in that variable are read as though they were typed at the command line before the ones you actually type.

So you might set HEBCAL_OPTS to be

--geo 44.0181,-88.6353 -z America/Chicago

and if you type hebcal -ch hebcal will think you typed hebcal --geo 44.0181,-88.6353 -z America/Chicago -ch

For information on setting environment variables, consult your local guru.

Danny Sadinoff

With contributions from

• Michael J. Radwin
• Eyal Schachter (JavaScript port)
• Aaron Peromsik (Daf Yomi, experimental zmanim feature)
• Ben Sandler (Molad and daily Sunrise/Sunset features)

calendar(1), emacs(1), hcal(1), hdate(1), omer(1), remind(1), rise(1)

The latest version of the code will be available from https://github.com/hebcal/hebcal

The original motivation for the algorithms in this program was the Tur Shulchan Aruch.

For version 3, much of the program was rewritten using Emacs 19’s calendar routines by Edward M. Reingold and Nachum Dershowitz. Their program is extremely clear and provides many instructive examples of fine calendar code in emacs-LISP.

For version 4, candle-lighting times were rewritting using Derick Rethans's timelib.

Version 5 was ported from C to Go.

A well written treatment of the Jewish calendar for the layman can be found in Understanding the Jewish Calendar by Rabbi Nathan Bushwick. A more complete bibliography on the topic can be found there, as well as in the Encyclopedia Judaica entry on the calendar.

hebcal help

Prints a shorter version of this manpage, with comments on each option.

hebcal info

Prints the version number and default values of the program.

hebcal cities

Prints a list of cities which hebcal knows about, suitable as arguments to the −C city option.

hebcal copying

Prints the GNU license, with information about copying the program. See below.

hebcal warranty

Tells you how there’s NO WARRANTY for hebcal.

This is just a program I wrote during summer school and while avoiding my senior project. It should not be invested with any sort of halachic authority.

Hebrew dates are only valid before sundown on that secular date. An option to control this will be added in a later release.

When using the legacy -L flag, negative longitudes are EAST of Greenwich.

Some combinations of options produce weird results, e.g. hebcal -dH nisan 5744 hebcal -dH 5744 This comes into play when you use the HEBCAL_OPTS environment variable.

The sunup/sundown routines aren’t accurate enough. If you enter geographic coordinates above the arctic circle or antarctic circle, the times are guaranteed to be wrong.

Hebcal only translates between the Gregorian calendar and the Jewish calendar. It does not take into account a correction of eleven days that was introduced by Pope Gregory XIII known as the Gregorian Reformation. Wednesday, 2 September 1752 was followed by Thursday, 14 September 1752.

This means that the results will be at least partly useless where and when the Gregorian calendar was not used, e.g. before the 1752 in Britain and before circa 1918 in Russia. See "Gregorian calendar" on Wikipedia for a splendid chart depicting when the changeover from the Julian to the Gregorian calendars occurred in various places.

To build hebcal from the source repository, you'll need the following:

• Go version 1.13 or higher
• GNU make v3.79 or later

Once you have those, you can prepare the build environment as follows:

make clean all

Copyright (C) 1994-2011 Danny Sadinoff

Portions Copyright (c) 2011-2022 Michael J. Radwin. All Rights Reserved.

Hebcal is distributed under the GNU Public License. The program and its source code may be freely distributed. For details, see the file COPYING in the distribution.

If you are going to use this program, please drop me a line. I'd like to know who you are, what version you're using, and how you're using hebcal, and anything else you'd like to tell me, so that I can adjust the program to meet users' needs.

I am NOT demanding payment for the use of my program, but writing this program DID take time. The "free" in the GNU public license refers to distribution, not necessarily payment. Feel free to send $10 or multiples of $18 or just a postcard to me at my US Mail address (email me for it).

  send email to:
  danny@sadinoff.com