Tag: Zmanim

Updated Zmanim Jar Released – Please Download the Latest

In December when developing the Zmanim / Bearing to Yerushalayim map (blog post), I noticed a problem with the code used to generate zmanim. The API returns a Java Date object. Usually only the time is of interest, and the date is ignored, but in some cases (when a timezone offset is specified without using the Olson DB name (such as America/New_York) or if the GMT timezone is used for other locations, and the local standard time is calculated as an offset of GMT), the date of the sunset returned was earlier than the sunrise date. This caused zmanim such as sof zman Shema for some locations to be incorrect, since the math used was comparing sunrise to a sunset on the incorrect date, causing some very odd behavior. Updated files that correct this issue were uploaded to the site on Dec 26th. I was notified today by a developer using the jar, that not all the download links were pointing to the updated versions, and this caused issues for his program (a post about his project will be posted in the near future). All the links have now been updated. Since the old code can sometimes generate incorrect zmanim, it is highly suggested that you replace your current jar with the latest version of zmanim.jar (or zmanim.zip).

Along with the fix mentioned above, a number of other small fixes were done. These include among other minor issues, fixed, better and simplified XML output from the toString method, better error handling for expected error conditions, that had previously caused errors in the generations of zmanim for areas in the arctic circle such as Thule, Greenland. In case you are curious, someone did actually try this, and the error logs lead me to find the issue. The IP address used for the request mapped back to the Thule Air Base.

Bearing to Yerushalayim and Zmanim Map



Did you ever find yourself unsure of the correct bearing (direction) to Yerushalayim (Jerusalem)? The new Zmanim/Bearing to Yerushalayim map will help you find it very easily. The map draws two lines from your location to Yerushalayim. The blue line uses the commonly used (לבוש Levush and others) rhumb line (a straight line on a Mercator projection map), while the green line shows the great circle route (Rabbi Aviad Sar Shalom Basilea הרב אביעד שר שלום באזילה in his אמונת חכמים Emunas Chachamim and others) on a map. While it appears that the circle line is not a straight line, on a globe, the shortest (and straightest) line between two points follows the great circle route. Future posts will detail the technical aspects of the work involved. For additional information of the correct bearing for tefila, see Rabbi Yehuda Herskowitz’s article in Yeshurun volume III page 586 and Rabbi Gavriel Goetz comprehensive pamphlet Gevuras Moishe on the subject.

How to Use

Find your exact location on the map by dragging the marker to your exact location or by clicking anywhere on the map. You can also click on the search button and enter your location (such as “Lakewood, NJ” (the default), “Vilnius, Lithuania”) or just enter a zip code (Canadian or British postal codes work as well) to zoom in on your location. Changing to satellite view and zooming in farther will make the job easier (assuming that you can identify your roof). Once the red marker is centered on your location, click the red marker to show your exact latitude, longitude and bearing to Yerushalayim in an info window. There are two additional tabs that show today’s zmanim. You can click on the “Link” button to refresh the page with the URL that contains coordinates to the currently displayed map with its zoom level so that it can be bookmarked or emailed.
I would like to thank Rabbi Yehuda Herskowitz for his excellent article and additional information that he provided.

Known Issues

Google Maps API Bugs (All Fixed by Google)

  1. Zmanim data sometimes fails to show in Firefox. This seems to be a bug in the Google Maps API when dealing with synchronous AJAX calls.
  2. Locations close to 180° from Yerushalayim (Alaska is a good test case) sometimes shows an incorrect rhumb line bearing (though the circle route shows correctly). The information in the info widow is correct. This is a known issue with the Google Maps API.
  3. Related to the above issue, sometimes the lines are drawn a “world away” and horizontal scrolling of the map is required to see the lines. Again this is a known Google Maps issue.

To Do (related to Zmanim)

  1. Support Daylight savings time (supported by the timezone webservice used, but not yet implemented in the map).
  2. Link to a yearly calendar.
  3. Elevation lookup (already available in the yearly calendar).
  4. Allow changing of the date.

Note that it is not clear that the Levush was of the opinion that the rhumb line should be used.

Zmanim Clock Applet Alpha Release

Java Logo Sepia
Note: Java Applets are obsolete, and the applet is no longer available
A while ago, Dr. Irv Bromberg mentioned to me, that my Zmanim API was in use in the Astronomical Clock Applet created by Ali Adams. The applet was a modification to Antony Pranata’s clock applet that displayed Islamic prayer times. Apparently the Zmanim API was so flexible that without any modification it was able to be used for generating “zmanim” well beyond anything I had envisioned. At Dr. Bromberg’s suggestion I modified the clock applet to display zmanim. Using the same Google Map API used in the Calendar Generator, I created the Zmanim Clock page (no longer available). The clock on the Clock page is very configurable, and allows selection of the location, zmanim etc. I contacted Antony Pranata, the original author of the clock who allowed my to release it under the GPL. An easy to use downloadable version will be made available in the near future. For those who think that the clock is upside down, there are more than enough configuration options to tweak the clock to your heart’s content.

Zmanim Calendar Generator Back Up (With Proper DST Rules)

Sunrise CalendarThe Zmanim Calendar Generator has been back up for about 2 weeks, but due to a downgrade in the Java version used, the DST issue that was as mentioned as fixed in a previous post returned. This has now been fixed using the Timezone Updater Tool. Please let me know if you run into any issues.