Kotel Compass

Software & tools Android Apps
1

Not new, and found in most siddurim apps, however I created a Kotel Compass as a first experience to publishing something on the Play Store. Kotel Compass by ShomerDNS.com

100% free and ad free

2

What position (:rofl:) do you take in the great “rhumb line vs. great circle” debate?

Your Google Play listing says:

A gold needle always points along the shortest path to the Kotel

That should have us in the US facing up to Canada…

3

The app calculates a true great-circle (spherical) initial bearing from your GPS location to the Kotel’s fixed coordinates (31.7767° N, 35.2345° E) — not a “flat map” straight line.

From the US, the needle would point northeast, not due east as a flat-map intuition might suggest. That’s because the shortest path over a sphere from most US locations to Jerusalem curves poleward, the same reason a NYC →Tel Aviv flight arcs up over the North Atlantic rather than flying a constant-longitude line.

Concretely, using the app’s exact formula:

  • New York City (40.71° N, 74.01° W) → bearing ≈ 54°, roughly NE (leaning toward ENE)
  • Los Angeles (34.05° N, 118.24° W) → bearing ≈ 24°, closer to NNE

So the farther west/north you are in the US, the more the needle swings toward true north; the farther east/south, the closer it swings toward due east. But it will land somewhere in the NE quadrant for virtually any continental US location, never due south or west.

4

Neither “rhumb line” nor “great circle” are a “flat map” straight line. They both follow the curvature of the planet, which we now know to be spherical. The difference between a “great circle” and “rhumb line” would be the difference between cutting the earth into two even halves, with the cut going through the current location and Jerusalem, while the “Great Circle” would slice the Earth in half unevenly. From NY, the rhumb line would head almost due north, while the great circle would be NE. The great circle maintains a constant compass heading - I.E. point a compass at jerusalem and head in that direction. Your compass is always pointing in the same direction the whole journey. Following a rhumb line is shorter, less miles than great circle, but compass head shifts. It looks like you describe great circle above, not rhumb line. If you read the article linked from myzmanim it will explain the difference - and maybe we in the US should really be facing Tzafon and not Mizrach. We’d get there quicker that way.

5

  1. Rhumb lines are straight lines on a flat map. That’s the entire reason the Mercator projection exists, it was invented specifically so a navigator could draw a straight line on paper and get a constant compass heading to steer the whole way. A great circle is the one that draws as a curve on a Mercator map (except along a meridian or the equator). So it’s backwards to say neither is a flat-map straight line, the rhumb line is exactly that.

  2. Great circles always bisect the sphere evenly, that’s their definition, not a special case. A great circle is any circle whose plane passes through the Earth’s center, so by construction it always splits the globe into two equal hemispheres (the equator, any meridian pair, the terminator all great circles, all even splits). A rhumb line (other than a meridian or the equator) isn’t even a closed circle, it’s a loxodrome, a spiral that winds toward the pole without ever closing up or symmetrically dividing anything. So the “even vs. uneven” distinction is reversed.

  3. The great circle is, by definition, the shortest path between two points on a sphere. The rhumb line is equal or longer, never shorter. That’s not an empirical claim, it’s what “great circle” means, it’s the geodesic. A rhumb line trades distance for convenience (constant heading, no need to keep adjusting your compass), which is exactly why ships and planes plan great-circle routes to save fuel/time and only historically preferred rhumb lines for ease of steering.

So “facing Tzafon to get there quicker” doesn’t work either way: the rhumb line isn’t due north from NYC (it’s due east), and even if it were, it would be a longer path than the great circle, not a shortcut the great circle already is the shortcut, by definition.

6

Here is the link again.

Although the truth is, I mixed up rhumb and great circle - got them backwards. However, neither of them is a flat map line. A flat map line would point SEE. The question here is if we head constantly in one direction, not turning right or left, and maintaining a constant heading (imagine traveling AROUND the Earth along a line of latitude) as opposed to travelling over the top which would be quicker, but on a constantly changing heading. (For the 1st half of the journey, we’d be travelling NNE, then SSW after passing the pole. This is the route airplanes take, flying up to Quebec, over Greenland, back down over turkey.

Click on 3d map here, you will see great circle route:

This is an argument in semantics. (explain that to your AI). Rhumb line is NOT flat map. It LOOKS FLAT when written on a mercator because mercator is a distortion. Looking at a globe, and drawing a straight heading line to JLM you will see the it is also curved, and more miles than great circle, but not flat. - just keeping a constant heading, so LOOKS flat on the mercator. (It can’t be flat because the Earth isn’t flat)…

Whatever

The key problem is that you’re applying the modern mathematical/navigation definition of “straight” to a question that MyZmanim explicitly says is about two different definitions of straightness.

MyZmanim actually agrees with several of your mathematical statements. The part you’re missing is what the rhumb-line position means in the halachic discussion.

1. Yes, a rhumb line is straight on a Mercator map — but that’s not the relevant distinction

MyZmanim defines the two routes this way:

“The term rhumb line is used to describe a route that is straight in the sense that it maintains constant compass direction.”

And:

“The term great circle path is used to describe a route that is straight in the sense that it is neither bearing right nor left.”

So you are correct that a rhumb line is the line that appears straight on a Mercator projection and maintains a constant compass bearing.

But MyZmanim isn’t saying otherwise.

The disagreement is over what “straight” means on the curved Earth:

  • Rhumb-line definition: “I keep my compass pointed at the same bearing.”
  • Great-circle definition: “I don’t turn/bear left or right.”

Those are different concepts on a sphere.

2. The important example is New York → Israel

This is where your argument actually gets reversed.

MyZmanim specifically says that from New York, the rhumb-line route to Israel starts at approximately 96° — essentially due east. You maintain that compass heading all the way.

But here’s the crucial point:

You are NOT traveling along a great circle.

You’re traveling along a small circle/loxodrome, and as you proceed eastward you are continuously bearing left relative to the Earth’s surface.

MyZmanim explicitly describes this:

“although he has been maintaining a constant heading throughout his journey, in doing so he was also continuously bearing left.”

So when MyZmanim says the rhumb-line route is “straight,” it means straight according to the constant-bearing definition, not “a geodesic.”

That’s precisely the distinction the article is making.

3. Your statement that the rhumb line is “due east” actually supports MyZmanim

You said:

“the rhumb line isn’t due north from NYC (it’s due east)”

Correct.

And MyZmanim says exactly that:

Rhumb line from New York → Israel: 96°, approximately East.

The disagreement isn’t about whether it’s east.

It’s about whether “facing east” constitutes facing toward the Beis Hamikdash.

According to the rhumb-line approach discussed by MyZmanim: yes.

According to the great-circle approach: no — you initially face approximately 54° (northeast).

4. And here’s the part that directly defeats the “great circle is always the shortcut, therefore rhumb is wrong” argument

You’re absolutely correct mathematically:

A great circle is the shortest route between two points on a sphere.

But that doesn’t establish that the great-circle route is the halachically intended meaning of “straight.”

MyZmanim explicitly presents this as a machlokes among Rabbonim:

“Whether the Torah definition of ‘straight’ follows the rhumb line model or the great circle model, is a subject of disagreement among Rabbonim.”

And it deliberately gives both calculations.

In fact, its example demonstrates the distinction beautifully:

Rhumb line:

  • Start NYC at 96°.
  • Keep the compass at 96°.
  • Arrive in Israel.
  • Distance: about 6,100 miles.
  • You have continuously borne left.

Great circle:

  • Start NYC at 54°.
  • Follow the geodesic without bearing left or right.
  • Arrive in Israel.
  • Distance: about 5,670 miles.
  • Your compass heading continuously changes along the journey.

So yes: the great-circle route is shorter.

That’s not in dispute.

The question is whether shortest/geodesic is what the Torah means by derech yesharah / a straight path for purposes of determining the direction to face.

5. Your “rhumb line isn’t a straight line” argument is therefore arguing past the article

You are essentially saying:

“A rhumb line isn’t actually straight because it’s not a geodesic.”

MyZmanim’s answer is:

That’s one definition of straight.

The article deliberately gives another:

constant compass bearing = straight in the rhumb-line sense.

That’s why the article starts by saying that on a curved Earth, a “straight path” can mean two different things.

And it gives an excellent thought experiment: stand 30 feet from the North Pole and walk east while maintaining the same compass heading. You eventually return to your starting point. Clearly that isn’t “straight” in the geometric/geodesic sense — but it is straight in the constant-bearing sense.

6. One thing you said that is particularly misleading

You wrote:

“A rhumb line … is a loxodrome, a spiral that winds toward the pole without ever closing up or symmetrically dividing anything.”

That’s mathematically reasonable as a general description of a non-special-case rhumb line, but it’s irrelevant to the question being discussed.

The question isn’t:

“Is a rhumb line a great circle?”

It obviously isn’t.

The question is:

“When the halachic instruction is to face toward the Beis Hamikdash along a ‘straight’ path, does ‘straight’ mean constant compass bearing or a non-bearing/geodesic path?”

MyZmanim says there are Rabbinic authorities on both sides, and therefore provides both directions.

So the strongest correction to your original three points is:

You’re mathematically correct about what a rhumb line and great circle are. But you’re using those definitions to answer a question that MyZmanim explicitly frames as a dispute over two different meanings of “straight.” The fact that the great circle is shorter does not prove that it is the halachically relevant definition of straightness.

And, importantly, MyZmanim itself gives the rhumb-line position as the position of HaRav Yisroel Belsky and others, while giving the great-circle position as that of HaRav Yechiel A. Zilber and others. For example, its current Woodmere calculation gives 96° (east) for the rhumb line and 54° (northeast) for the great circle.

So if the guy’s argument is “MyZmanim’s rhumb-line explanation is geometrically wrong,” he’s wrong about that. If his argument is “the great-circle approach is mathematically the geodesic/shortest route,” he’s right — but that doesn’t settle the halachic question MyZmanim is addressing.

Point is - if you adopt a great circle approach, (even if more intuitive) you are going against the levush and classic poskim that relied on mercator projection and promoted mizrach. By adopting great circle over rhumb, you are choosing tzafon. So you are taking a position in the debate… Eliyahu Hershfeld’s map shows both.

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The planes fly the great circle route NNE. Rhumb is almost due E.

As you can see, in this projection (not mercator) the rhumb is not straight.

7

This is a great debate.

Chabad.org is one voice, not the last word but a view I follow that lean towards, the “Great Circle Approach” They have an article at, https://www.chabad.org/library/article_cdo/aid/3502321/jewish/Why-Do-We-Face-East-Weight-Praying-Or-Do-We.htm

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8

The compass shows the same direction; it is better for it to constantly point toward North and the direction of prayer.

9

Line up the white arrow on the dial with the gold line at the top, when these are aligned you will see a Magen Dovid, then the direction of the white arrow is the direction you face.

Did i get this right or did you mean something else?

10

i don’t pray to a rock.

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Either way, I usually just face the front of the shul, whatever it faces, rhumb, great circle, (or in your case, eastern parkway).

12

(Just to add to the confusion)

There is significant evidence that the world is FLAT (or a dome) and not a sphere. In which case…

13

K if we’re getting specific, 770 faces Kingston avenue :melting_face:

14

Pray do share.

Then nothing changes, if the dome corresponds to the northern hemisphere. (I wonder where all the people in southern hemisphere would go in this dimension of logic?) Even if the dome extends to include the southern hemisphere, (Which anyway couldn’t accurately be called a hemisphere in this scenario), the calculations for the northern hemisphere, which encompasses both Jerusalem and New York, would remain the same. So big difference between a dome and flat.

Then we must be discussing which way to face inside the tunnel.

15

I’ve seen the sphere shape of the earth on a very high transcontinental flight.

16

I pray toward Mizrach because the Shechinah is there. It has nothing to do with some wall that people cry to and a country decided is somehow holy. And let’s not forget: without it, the country basically has no cool monument to drag bribed world leaders to.

But yes — praying to a rock is no different to me than praying toward the black box in Mecca. They also don’t say, “the box is God.” They say it’s holy, special, has some spiritual significance, etc. Same idea.

The Western Wall is a historical wall according to some sources. And today the place is full of filth and has been turned into a label and symbol of a movement that is against the Torah.

So no, people should not go there. For sure not specifically to pray there. For sure not kiss the wall. And for sure not stick notes into cracks as if the wall can read them.

Mizrach? Yes. Because of the Shechinah.

The wall itself? It’s a wall.

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מעולם לא זזה שכינה מכותל מערבי (שמות רבה פרשה ב’, סימן ב’)

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Don’t forget the cosmic turtle

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Orach Chayim 2, 113

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There are many things that changed. Al-Aqsa used that wall - would you still say so?