Which Way Is Mizrach? Great Circle, Rhumb Line or Direct East

Image credit: MathWorks

A new version of our iPhone Siddur is now available for download, as a free upgrade. I wanted to share one of the many changes we made to the application.

We added a feature to change how we calculate the Mizrach compass.  Up until now, we've been using a formula known as the Great Circle Method.  This, in my opinion, was the most accurate way to calculate the direction a Jew needs to pray to reach Jerusalem.  Other opinions are to use Rhumb Lines or to point directly East as was done in many European synogogues.

I had a user who would no accept my Great Circle direction because he always felt it was wrong.  He is entitled to his own opinions.  After like 30 emails, he convinced me to add more options to Siddur.  So I did.

In laymans terms, the following are the options:

1. Great Circle (default) - the path which airplanes take.  North-East from NY area.
2. Rhumb Line - the path which mostly ships take.  East from NY area.
3. Directly East - the compass direction of East.

I am not going to go into too many details because there are good links for that:

• MyZmanim, a prominent site for prayer times, has a great overview of all of this.
• KosherJava, the place where we ported our Zmanim code from, has a very technical blog post and seemed happy we added the options to Siddur.

  Great to see that @iSiddur now has a great circle compass option. Was the uber accurate Vincenty formula used? http://bit.ly/bu0uPyless than a minute ago via TweetDeckKosher Java
  KosherJava

• To answer Kosher Java, all of our formulas were adapted from: http://www.movable-type.co.uk/scripts/latlong.html

As always with this stuff, please don't rely on technology.  If a gps tells you to jump off a bridge, don't.  Be smart.  If the compass is pointing to the South Pole, you know there has to be some interference.  Ask a Rabbi if you are unsure of your custom.  Whenever with a Minyan or at a Shul or Synagogue, always follow the crowd.  My Shul davens on the South wall due to problems placing the Aron Kodesh on the East wall.

Don't be afraid to ask.  That is why I added these options in the first place.  There is no right or wrong formula!

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