FAQ: How do I Calculate the Jewish/Hebrew Date for …?

Sunrise Calendar

This FAQ is now obsolete. Jewish Calendar Calculations are now supported. See the Zmanim API 1.3.0 Release announcement

Question:

How do I get the Jewish Date for … using the Zmanim API?

Answer:

The current version of the Zanim API does not support Jewish calendrical calculations. Zmanim are almost exclusively based on the solar calendar, so for example, the sunrise on February 8th this year in Montreal (or any other date and location), will be almost the same every year. for this reason there was little point (as far as zmanim) to support Jewish date calculations in the API. One of the only zmanim to rely on a Jewish date is the sof zman kidush levanah calculation, though there are some opinions that it is purely molad based, and this can be calculated without a Jewish calendar component to the API. This zman is obviously not currently implemented in the Zmanim API. I am currently working on adding Jewish date support to the API. The code is based off Avrom Finkelstein‘s no longer active HebrewDate project. I refactored a lot of the code and fixed a number of bugs. Anyone interested in alpha testing this code can download the latest Zmanim SVN code.
I mentioned that it “will be almost the same every year” and this is due the approximate 1/4 day drift between the 356 day calendar year and the approximately 365.25 days actually present in the astronomical year, a discrepancy corrected every leap year. A future FAQ (probably a few of them) may delve specifically into this drift as well as general zmanim accuracy issues in detail.
If you are simply looking to convert a Hebrew date to Gregorian or Gregorian to Hebrew online without the API, try the JewishGen calendar conversion tools.

FAQ: Why Some Zmanim Never Occur (Developers Beware)

Question:

Why do some zmanim never occur in some locations? Developers Beware!

Answer:

While most people realize that the sun may not rise or set in the Arctic and Antarctic Circles (see the Rabbi Dovid Heber’s article When Does One Pray When There Is No Day in the Star-K’s Kashrus Kurrents), many are not aware that some twilight dips will not occur during part of the year as far south of the Arctic Circle as London. For example around the summer solstice in London (on the zmanim map) the sun will never dip far enough below the horizon to reach alos 16°. This happens in London from June 4th through July 8th. The image seen on the top right (original at timeanddate.com) shows various civil twilights centered on London on Midnight June 21st. Look carefully to see the various bands of twilight. Gateshead will not have alos 16° from May 16th through July 28th, while Anchorage, Alaska (yes there is a Frum Shul in Anchorage with an interesting davening direction issue that is discussed in the Davening Direction from Alaska post ) will not have alos 16.1° from April 25th to August 20th. Zmanim based on sunrise such as alos 72 that is a 72 minute offset of sunrise can be calculated as long as sunrise can be calculated, something that will happen as long as you are not in the Arctic or Antarctic Circles.
For this reason, the Zmanim API will return a null when a zman will not happen. A Long.MIN_VALUE will be returned when a long is expected such as in the case of a shaah zmanis. While an inconvenience to developers who have to code for this, the alternative of a default date would mean that developers unaware of this would return incorrect zmanim, something far worse than a program error from a NullPointerException.
In recent weeks two publicly available programs using the Zmanim API ran into issues due to nulls returned for early alos times. Being something not anticipated by the developers, the nulls generated errors in the programs that quickly led to fixes. For this reason, Yitzchok updated the Zmanim .NET project to return the nullable DateTime? instead of the regular DateTime that it had previously been returning. While the Zmanim API documentation always made the possibility of a null being returned possible, I modified the documentation to make this clear on the return value documentation for every zman. Code with the modified documentation was part of the recently released Zmanim API 1.2.1.

Zmanim API 1.2.1 Released

The Zmanim API 1.2.1 was released today. Changed in this release were the addition of a few very early Tzais zmanim, and the removal of references to the GregorianCalendar in favor of the base Calendar class to ease Noah Blumenthal’s use of the Zmanim API in a zmanim application for the BlackBerry. This change has no impact on functionality as tested using Yitzchok’s new JUnit tests. Additionally, the JavaDoc Zmanim API documentation was modified to clearly indicate that zmanim can return nulls. A followup post will have details on this.
The main download is the Zmanim 1.2.1 release zip file that includes source files and JavaDoc documentation. Also available for download (included in the above zip file) is the main zmanim-1.2.1.jar and the zmanimAstronomical-1.2.1.jar that only includes the AstronomicalCalendar. The removal of the GregorianCalendar was in this class. Additional detail on the downloads can be seen on the Zmanim Download page

Zmanim API Ported to .NET (C#)

Yitzchok ported the Zmanim API from Java to a .NET API using C#. The Zmanim .NET project was released under the LGPL 2.1. This is a change from the GPL used by the Java API, something that may change shortly. Also part of the project was the creation of a C# version of the Zmanim CLI, matching Moshe Wagner’s Java Zmanim CLI. When developing the project, Yitzchok created the ZmanimTest JUnit test case class to confirm that the C# port output matched the Java API. I will likely add this to the core Zmanim API in the near future. The port currently relies on IKVM assemblies as can be seen in the Java references in the code sample below, mostly because of the lack of a native .NET equivalent of the Java TimeZone class. Yitzchok also created some examples of the use of the Zmanim .NET API that will be of help to developers. Below are two of the simpler examples in C# and VB.NET demonstrating a very simple use of the API to output zmanim from the console.

C#

using Zmanim.TimeZone;
using Zmanim.TzDatebase; //in Zmanim.TzDatebase.dll assembly
using Zmanim.Utilities;

namespace Zmanim.Samples.Console
{
    class Program
    {
        static void Main(string[] args)
        {
            string locationName = "Lakewood, NJ";
            double latitude = 40.09596; //Lakewood, NJ
            double longitude = -74.22213; //Lakewood, NJ
            double elevation = 0; //optional elevation
            ITimeZone timeZone = new OlsonTimeZone("America/New_York");
            GeoLocation location = new GeoLocation(locationName, latitude, longitude, elevation, timeZone);
            ComplexZmanimCalendar zc = new ComplexZmanimCalendar(location);
            //optionally set it to a specific date with a year, month and day
            //ComplexZmanimCalendar zc = new ComplexZmanimCalendar(new DateTime(1969, 2, 8), location);

            System.Console.WriteLine("Today's Zmanim for " + locationName);
            System.Console.WriteLine("Sunrise: " + zc.GetSunrise()); //output sunrise
            System.Console.WriteLine("Sof Zman Shema MGA: " + zc.GetSofZmanShmaMGA()); //output Sof Zman Shema MGA
            System.Console.WriteLine("Sof Zman Shema GRA: " + zc.GetSofZmanShmaGRA()); //output Sof Zman Shema GRA
            System.Console.WriteLine("Sunset: " + zc.GetSunset()); //output sunset

            System.Console.WriteLine("Press enter to exit.");
            System.Console.ReadLine();
        }
    }
}

VB.NET

mports Zmanim.TzDatebase 'in Zmanim.TzDatebase.dll assembly
Imports Zmanim.Utilities
Imports Zmanim.TimeZone

Module Module1

    Sub Main()
        Dim locationName As String = "Lakewood, NJ"
        Dim latitude As Double = 40.09596 'Lakewood, NJ
        Dim longitude As Double = -74.22213 'Lakewood, NJ
        Dim elevation As Double = 0 'optional elevation
        Dim timeZone As ITimeZone = New OlsonTimeZone("America/New_York")
        Dim location As New GeoLocation(locationName, latitude, longitude, elevation, timeZone)
        Dim zc As New ComplexZmanimCalendar(location)
        'optionally set it to a specific date with a year, month and day
        'Dim zc As New ComplexZmanimCalendar(New DateTime(1969, 2, 8), location)
        System.Console.WriteLine("Today's Zmanim for " & locationName)
        System.Console.WriteLine("Sunrise: " & zc.GetSunrise().ToString)
        'output sunrise
        System.Console.WriteLine("Sof Zman Shema MGA: " & zc.GetSofZmanShmaMGA().ToString)
        'output Sof Zman Shema MGA
        System.Console.WriteLine("Sof Zman Shema GRA: " & zc.GetSofZmanShmaGRA().ToString)
        'output Sof Zman Shema GRA
        System.Console.WriteLine("Sunset: " & zc.GetSunset().ToString)
        'output sunset
        System.Console.WriteLine("Press enter to exit.")
        System.Console.ReadLine()

    End Sub

End Module

The current Zmanim .NET TODO list for the project includes:

  • Remove dependency to Java (IKVM assemblies)
  • The API should follow the .NET guidelines
  • Make it Linq friendly
  • Add examples how to use this project in a ASP.NET MVC site and WPF Application
  • Try to get it to work on Silverlight

Android Zmanim Using the KosherJava Zmanim API

Android Logo
Android ZmanimThere are various software projects using the KosherJava Zmanim API. One of the active ones is Jay Gindin’s open source Android Zmanim app for the Android platform. Activity in the project is constant. The upcoming version allows the selection of a specific calculation for zmanim you want such as the zman Talis/Tefilin pictured here. There are plans to add direction to Yerushalayim functionality using the Zmanim API. (For more information on calculating bearing using the API, see Calculating the Bearing/Direction to Har Habayis Using the Zmanim API article.) A large part of Jay’s motivations for developing the code was lezecher nishmas his nephew Shemuel Reuven ben Yehudit Rachel who, lost his battle with cancer on October 21, 2009. The one very minor issue Jay had with the API (and documentation) was the Ashkenazi spelling of the zmanim names, something that as an Ashekenazi I do not plan to change :), but as you can see his Android Zmanim front end used Sephardi labeling. Asked how he found the project, he answered with the typical answer to this question

I Googled around, and found your project.

One of my goals with the API was to make it easy for developers to use and port. This was confirmed by Jay

I found it to be very easy to pull into my app, even on Android…no changes necessary, not even a recompile