Tag: Zmanim API

KosherJava Powers Zmanim on El Al Flights


In an earlier Inflight Zmanim Calculations – Why So Complex? post, I outlined the complexity of calculating zmanim for flights. Back in Aug 2022, Dan’s Deals posted the exciting news that Zmanim were added to El Al’s flight entertainment system. This had not been formally announced by El Al at the time since the app was really in an (unannounced) alpha/beta testing phase. A careful examination of the screenshots by members of the #zmanim channel in the Frum Software Developers Slack, showed that it was powered by the KosherJava zmanim library. It should not have been surprising that it was found and used without my knowledge, since it is a free, well documented and easy to use open source library. After a number of issues with the zmanim app were reported to me (I want to thank all of those who took the time to track me down to report the issues), Rabbi Dovid Heber reached out to El Al, and Tal Kalderon, the head of El Al’s Inflight entertainment & Connectivity team reached out to me for assistance. This lead to meetings with Boris Veksler the CEO of FlightPath3D who integrated the KosherJava zmanim code into their flight maps as an optional module that El Al is using.

The FlightPath3D in-flight mapping app on El Al with the zmanim app Magen Dovid icon on the bottom left
Boris made it a personal mission to perfect the product and a series of fixes were deployed until the final release of the Prayer Room / Mesivta Derakia app was deployed on El Al aircraft on 5 Feb, 2023. At this point, the app started displaying accurate zmanim. Boris and the FlightPath3D team put a lot of effort into perfecting it into an easy-to-use app. To ease understanding of zmanim on flights that cross time zones, the app shows countdown times to the upcoming zmanim.
The El Al Zmanim app showing the default current aircraft location zmanim
For example, El Al flight LY 26 from New York to Israel departing at 9pm will show a countdown to chatzos/midnight, alos hashachar (two variants) and later zmanim (such as misheyakir, sunrise, etc.), displaying a countdown, with the number of hours and minutes to upcoming zmanim. Zmanim are calculated based on the plane’s current location, speed and the flight path. Since headwinds and tailwinds (as well as in-flight route changes) can significantly change the time that zmanim will be reached, the times to the upcoming zmanim are recalculated multiple times a minute. This significantly reduces the challenge to passengers, since precalculated zmanim do not come close to real time calculations on the flight. The app also shows a compass with the bearing to Yerushalayim / Jerusalem (map). The FAQ that is part of the zmanim app on the aircraft appears in a hyperlinked version at El Al In-Flight Zmanim FAQ on this site. The app defaults to the Aircraft location but can be changed to show zmanim for multiple international cities
The El Al zmanim app displaying zmanim for New York
, displayed in the time and time zone of those cities. The app works in both English and Hebrew, based on the language selected in the flight entertainment system. A thank you goes to R’ Chaim Keller of the indispensable Chai Tables project for allowing the development team access his flight path algorithms. The FAQ would not have been possible without help of translators and copy-editors.
The El Al Zmanim app in Hebrew
A special thanks to Effie Freiner from Lakewood for the Hebrew translation (the “Yeshivish” Hebrew posed its own set of challenges), and to my wife and Dovid Nachfolger for clarifying the language and grammar in the English FAQ.
I spent time with Rabbi Dovid Heber, Rabbi Dovid Braunfeld, Rabbi Yisroel Harfenes and Reb Solly Tropper reviewing the various complexities of calculating in-flight zmanim before the app left the βeta stage and went live.

Developing Software for Aircraft

Developing apps for use on an airliner has a series of challenges, in particular for in-flight entertainment (IFE) systems. It is a complex process that requires a deep understanding of the aviation industry and the systems onboard the aircraft.

First, the hardware hosting the apps goes through stringent safety certifications and has to pass a series of requirements. These include being isolated from any cabin and aircraft controls. The most they can do is access the flight management system (FMS) in read-only mode, with no ability to push data to the FMS. These certifications are done for each aircraft configuration and can take a year or more to complete.

Software and the associated apps also follow similar certification processes. The software must be designed to work seamlessly with any IFE systems already in place on the aircraft. Thus, it has to adapt to new and older hardware and operating systems and understand and adapt to idiosyncrasies in the data provided by the FMS. FlightPath3D is a leading provider of interactive mapping software for IFE systems. This type of software provides passengers with real-time information about their flight’s location, altitude, and speed, as well as other relevant data such as the estimated time of arrival and the distance to the destination. This made FlightPath3D a natural vendor for the zmanim work. FlightPath3D has a wealth of experience in developing high-quality software solutions that meet the needs of airlines and passengers and adapt to the particular hardware installed onboard.

לז״נ אבי מורי הרב יצחק אריה בן ר׳ ברוך הירשפלד ז״ל. נפ׳ י׳ אדר ב׳ תשפ״ב.
In memory of my father R’ Yitzchok Hershfeld (Montreal).

Zmanim API 2.4.0 Released


The KosherJava Zmanim API version 2.4.0 was released on Nov 27, 2022 ד׳ כסלו תשפ״ג in Maven and GitHub.

New in Version 2.4.0

Tefila Rules Added to KosherJava Zmanim Library

Kosel Picture 1932
Davening at the Kosel. This picture was taken by my grandfather Sidney (Nesanel) Siegfried on Aug 1, 1932 כ״ח תמוז תרצ״ב. This article was posted exactly 90 years to the day (Gregorian date) after the picture was taken.
The new TefilaRules class has been added to the KosherJava Zmanim Library. This will be included in the upcoming v2.4.0 release. The TefilaRules class was added in an effort to help zmanim calendar authors who sometimes require knowing if תחנון tachanun is recited on a specific day in order to set tefila times (such as mincha starting X minutes before shkiah, and a few minutes later if tachanun is not recited). It is also useful for siddur app creators. With many different minhagim (mostly chasidishe) about when tachanun is recited, the class currently supports 12 different options that can allow setting the rules for a majority of minhagim.
Yahrzeits such as 7 Adar, (Moshe Rabbeinu’s yahrzeit) or holidays celebrated by specific communities such as Purim Mezhbizh (Medzhybizh) celebrated on 11 Teves or Purim Saragossa celebrated on the 17th of Shevat (the Wikipedia date seems to be in error), are not (and likely never will be) supported by this class.
Other tefila related rules such as the existing Mashiv Haruach etc. rules were moved over from the JewishCalendar class to this new class where they have a more natural fit. The methods that were migrated over, were deprecated in the JewishCalendar class and will be removed in v3.0.0.

Key Methods in the TefilaRules Class

The following are the key methods in the new TefilaRules class.

Sample Code

TefilaRules tr = new TefilaRules();
JewishCalendar jCal = new JewishCalendar();
HebrewDateFormatter hdf = new HebrewDateFormatter();
hdf.setHebrewFormat(true); // Hebrew formatting
jCal.setJewishDate(5783, JewishDate.TISHREI, 1); // Rosh Hashana
System.out.println(hdf.format(jCal) + " - Is tachanun recited: " + tr.isTachanunRecitedShacharis(jCal));
jCal.setJewishDate(5729, JewishDate.SHEVAT, 21);
System.out.println(hdf.format(jCal) + " - is mashiv haruch recited: " + tr.isMashivHaruachRecited(jCal));
jCal.setJewishDate(5783, JewishDate.ADAR, 17);
System.out.println(hdf.format(jCal) + " - Is tachanun recited: " + tr.isTachanunRecitedShacharis(jCal));
tr.setTachanunRecitedWeekOfPurim(false); //default is true
System.out.println(hdf.format(jCal) + " - Is tachanun recited: " + tr.isTachanunRecitedShacharis(jCal));

Output:

א׳ תשרי תשפ״ג - Is tachanun recited: false
כ״א שבט תשכ״ט - is mashiv haruch recited: true
י״ז אדר תשפ״ג - Is tachanun recited: true
י״ז אדר תשפ״ג - Is tachanun recited: false

Zmanim API 2.3.0 Released


The KosherJava Zmanim API version 2.3.0 was released on Dec 7th, 2021 ג׳ טבת תשפ״ב in Maven and GitHub. While there have been numerous releases over the years, this is the first release-related post since the v1.3.0 release in 2013. If you have not updated since that time, you can expect some changes. The most significant changes (besides a lot of new functionality) are the simple to fix breaking changes listed below.

New in Version 2.3.0

The list of significant changes in this and previous releases can be seen in the KosherJava Zmanim API changelog.

Breaking Changes since v1.3

The Yereim’s Bein Hashmashos

Rabbi Eliezer of Metz (known by his acronym The רא״ם Re’em), a disciple of Rabbeinu Tam, in his Sefer Yereim ספר יראים chapter 274, states that bein hashmashos starts the time it takes to walk three quarters of a mil before sunset, and ends at sunset.

פירוש משתשקע החמה דר׳ יהודה ור׳ נחמיה משמתחלת לשקוע שנוטה מעט ומכירים העולם שרוצה להכנס בעובי הרקיע … ולשון משתשקע משמע הקדמה … וכן נראה לי עיקר דמשתשקע החמה הוא קודם שקיעת החמה דעולא ולא כדברי רבינו יעקב … ואין להקפיד על צאת הככבים … אע״ף שאין הכוכבים נראים … שלילה גמור הוא כפירושי.

The Yereim’s opinion is brought down by other Rishonim including the Mordechai and Rav Alexander Suslin HaKohen in his Sefer Agudah. The Yereim is mentioned by the Bach as a reason for the minhag of starting Shabbos early. The Yereim’s times are not brought down by the poskim lehalacha.

The Time to Walk a Mil

The time to walk a mil is based on the Gemara in Pesachim 93b – 94a. The time ranges in the poskim and includes 18, 22.5 and 24 minutes. Three quarters of these mil times would be 13.5, 16.875 and 18 minutes. It should be noted that the Yereim is of the opinion that a mil is 24 minutes. The above mentioned Mordechai who quoted the Yereim is also of the same opinion. We will hopefully discuss in detail the various opinions on the time to walk a mil in a future article.

The Addition of the Yereim’s Times to the KosherJava Zmanim Library

As of the 2.1.0 release of the KosherJava zmanim library, the Yereim’s bein hashmashos times have been added to the KosherJava zmanim library/API. There are six variants of these zmanim that were added. These include the three exact minute offsets mentioned above, as well as the conversion of these three times to degrees (elevation angle, or solar zenith angle). The only prior degree based time for the Yereim that I am aware of is in Rabbi Yedidya Manet’s Zmanei Halacha Lema’aseh (זמני ההלכה למעשה מהרב ידידיה מנת). The Zmanei Halacha Lema’aseh charts calculate bein hashmashos in degrees based on the 18 minute (3/4 of a 24 minute mil, see p. 27 in the 4th ed. published in 2005), but does not clarify the degrees used. At Rabbi Yaakov Shakow’s recommendation, I used the refraction value of 31/60 or 0.516° that exists in Israel, as opposed to the global average of 0.566°. This more stringent refraction is mentioned in the Zmanei Halacha Lema’aseh (p. 11) and used in the לוח עתים לבינה Luach Itim Lebinah. I also slightly rounded the times. These small tweaks resulted in a trivial maximum 19 second chumra vs the non-rounded global average refraction. The resulting degrees of elevation angle for the Yereim’s bein hashmashos are 2.1°, 2.8° and 3.05°. Solar zenith angles are traditionally calculated using the sun’s position without adjusting for refraction and without accounting for the solar radius (i.e. it is the position of the center of the sun in a vacuum). This does not impact the calculated time, it is simply the convention used. In the upcoming 8th edition of הרב דוד יהודה בורשטין Rabbi Yehuda Burstein’s זמנים כהלכתם / Zmanim Kehilchasam he mentions that

הזמן הנ״ל של 18 דקות לפני השקיעה המישורית הוא הזמן רק במרכז א״י ביום הבינוני כנ״ל, ובכל מקום בכל יום מחשבין זאת לפי שיטת המעלות, דהיינו דבודקים כמה מעלות מעל האופק נמצאת השמש במרכז א״י ביום הבינוני 18 דקות לפני השקיעה המישורית, ואותו מספר מעלות של השמש מעל האופק בכל מקום בכל יום הוא הזמן של ״היראם״. ועוד יש להוסיף זמן ל״תוספת שבת״, ובזה יוצא ידי כל שיטות הראשונים ואשרי חלקו.

A future article will address the proper date to use for converting minute-based times to degrees below (or above) the horizon and show how to use the KosherJava Zmanim code to calculate this.
I would like to thank Rabbi Yaakov Shakow for his help and suggestions.

Sample Code

Below are code examples for all six variants of the Yereim’s Bein Hashmashos (spelled BainHashmashos in the code).

GeoLocation yerushalayim = new GeoLocation("Jerusalem, Israel", 31.778, 35.2354, 0, TimeZone.getTimeZone("Asia/Jerusalem"));
ComplexZmanimCalendar czc = new ComplexZmanimCalendar(yerushalayim);
Date bh18Min = czc.getBainHasmashosYereim18Minutes();
Date bh3Pt05Deg = czc.getBainHasmashosYereim3Point05Degrees();
Date bh16Pt875Min = czc.getBainHasmashosYereim16Point875Minutes();
Date bh2Pt8Deg = czc.getBainHasmashosYereim2Point8Degrees();
Date bh13Pt5Min = czc.getBainHasmashosYereim13Point5Minutes();
Date bh2Pt1Deg = czc.getBainHasmashosYereim2Point1Degrees();

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd h:mm:ss a z"); //set the output format
sdf.setTimeZone(czc.getGeoLocation().getTimeZone()); //set the formatter's time zone
System.out.println("Bein Hashmashos 18 min:     " + sdf.format(bh18Min));
System.out.println("Bein Hashmashos 3.05°:      " + sdf.format(bh3Pt05Deg));
System.out.println("Bein Hashmashos 16.875 min: " + sdf.format(bh16Pt875Min));
System.out.println("Bein Hashmashos 2.8°:       " + sdf.format(bh2Pt8Deg));
System.out.println("Bein Hashmashos 13.5 min:   " + sdf.format(bh13Pt5Min));
System.out.println("Bein Hashmashos 2.1°:       " + sdf.format(bh2Pt1Deg));

The output of the above code (assuming that the calendar was set to March 16, 2020).

Bein Hashmashos 18 min:     2020-03-16 5:29:58 PM IST
Bein Hashmashos 3.05°:      2020-03-16 5:29:40 PM IST
Bein Hashmashos 16.875 min: 2020-03-16 5:31:05 PM IST
Bein Hashmashos 2.8°:       2020-03-16 5:30:51 PM IST
Bein Hashmashos 13.5 min:   2020-03-16 5:34:28 PM IST
Bein Hashmashos 2.1°:       2020-03-16 5:34:09 PM IST