No. Depending on which landmark you picked en route, you would wind up with a different compass direction. Something that bears remembering in this discussion is that, in general, great circle routes are not a constant compass direction. From here in the Bay Area, my qibla is about 19 degrees and change (from true north). If I were to follow that great circle route to Mecca, that heading would change as I traveled. Drastically, in fact.
The “normal” map you can read compass directions from is the Mercator projection. That was the main purpose for its creation. Compass directions come out as straight lines. The so-called “rhumb line” course between two points can be computed from plotting on a Mercator map and following a constant compass heading. It generally comes out as a curve when drawn on the globe.
I said calculator and obviously you can use a spreadsheet to instantly calculate azimuth and distance to any place in the world. It is the simplest thing.
i know we all hate to restrict ourselves to the OP which was:
>> I once saw, in a museum, a compass-like pocket device for finding the Qibla. How do these things work?
The correct answer is that with the information given there is no way to know what the heck he saw and even if the information given with it was correct and interpreted correctly. We would need more precise information about the instrument and about what the text said about it.
It could have just made a very general assertion that meant astronomy was used to determine qibla.
Since the OP never returned to clarify we will be left in the dark
yabob, I understand that. I would obviously have to pick somwhere very close to where I am. If I had an azimuthal map where I could draw a line from here in Troy, NY to Mecca, and it went through, say, Petersburg, NY (less than 30 miles away), I could point myself in the direction of Petersburg. I can get a compass bearing from a normal map (for the distance covered, a conical projection would work as well). Sure, I’d be off by whatever the difference is between a rumb line from here to Petersburg and the great circle direction. For the distance involved, I’d say it’s negligible.
Obviously, Newfoundland is a less precise approximation. The line also seems to go through southern France. That would be wildly innaccurate, of course. OK, it’s a two step process, as opposed to the one step process that an azimuthal map centered on me would be, but it wouldn’t require a collection of azimuthal maps for every possible location.
Actually, if I had a huge version of the map centered on Mecca, and it had latitude and longitude lines (errr, circles or something), couldn’t I get my coordinates and the coordinates of a spot along the line from me to Mecca (again, a nearby spot) and figure out the distance algebraically? I don’t see any reason that that would be impossible. Not that this has anything to do with the OP, as I’m sure that the object in question wasn’t a pocketsized huge azimuthal map of the earth.
waterj2, while I am a bit confused by the way you say it I believe the underlying idea is correct (although maybe not too practical).
If I am in DC and I have an azimutal map centered on Mecca, if I drwa a straight line from Mecca to DC, all the points along that line have the same azimuth from Mecca. If the twown of Goalesville is in the same like I know that if I face in the direction of Goalesville, I am also facing Mecca. The principle is sound.
In practice though you probably would have to get a local map and find the bearing of Goalesville.
In practical terms it seems to me calculating the Azimuth directly is far simpler than any of the other proposed solutions.
No, it wasn’t an astrolabe. What if you had an azimuthal map and knew where you were? Couldn’t you then figure out the direction from mecca to your current location, and face the opposite direction?
>> What if you had an azimuthal map and knew where you were? Couldn’t you then figure out the direction from mecca to your current location, and face the opposite direction?
>> Is there any easy way to generate an azimuthal map for any point on earth?
I already answered this and the answer is still NO. The azimuth from your place to Mecca is not the opposite of the azimuth from mecca to your place. You would need an azimuthal map cetered in your position. An azimuthal map is generated by computing distance and azimuth to thousands of known places. You can have one easily generated at this site. But since you only want the azimuth to Mecca there is no pint in calculating the rest of the map.
Two points on the surface of the Earth (plus the center of the Earth) define a Great Circle. Imagine the great circle defined by Mecca and Washington DC.
Roughly: DC = 39N 77W - - Mecca: 18N 40E
Azimuth from Mecca to DC: 316
Azimuth from DC to Mecca: 59
Note that both have N component and are therefore not opposite. Note that unless two places are on the same meridian, the azimuth from place1 to place2 will have a E component and the azimuth from place2 to place2 will have a W component. This is not true of N and S. The azimuth from DC to Mecca has a N component and the azimuth from Mecca to DC also has a N component.
Think about this also: All the places located along this great (semi)circle have the same azimuth from Mecca and yet there are NO two places on this great circle for which the azimuth of Mecca is the same. The Azimuth of Mecca keeps changing as you travel along the great circle.
Corollary: ANY Great circle that passes through Mecca has a point where the azimuth of Mecca is 90 (E) and another point where it is 270 (W)
The distance from DC to Mecca is greater tha 90 degrees and, therefore, when the Sun is over Mecca it will not be visible from DC. It could be seen from Newfoundland though.
That’s the link I posted and referred to several times in this thread.
And another tidbit to add is that both the azimuth from A to B and the azimuth from B to A will have north components if A and B are both north of the equator. Another is that the points you referred to in your corollary will be the northernmost and southernmost points on the great circle. Also, the great circle containing Mecca and the directly opposite it on the world will not contain any points where the azimuth is 90 or 270.
OK, that first tidbit I mentioned is obviously wrong, now that I think about it. However, the converse is true, I think: if the azimuths both have a North component, both points must north of the equator. As for the second tidbit, I wasn’t nearly specific enough, as both points fall on all great circles from Mecca. There are two such great circles, the one that goes through the north and south poles, and the one perpendicular to that one.
However, I have come up with an idea for a mechanical device that could derive a qibla azimuth from a location on earth. I’ll try to describe it as simply as possible. Imagine a globe of the earth. Now imagine that there is a ring around it which is attached at the poles and can move freely east and west to lie over any meridian.
Next, imagine a similar ring, except that the points where it is attached are Mecca and anti-Mecca. It would not be hard to place a disc on the north-south ring in such a way that it was always placed over the intersection of the rings. And then, it would not be hard to place a needle on that disc that always points along the direction of the other ring. This would from a dial showing the direction of qibla at the point over which the rings intersect.
Obviously, this is not the indicator in question, but it does show that it is possible to mechanically derive quibla at a given point. It should be possible to condense this method into a 2-dimensional indicator.
waterj2, of course a model of the globe would work, but this is hardly convenient (or ingenious). Not to mention that for it to have any degree of accuracy it would have to be huge.
I have a better idea. I have made a spreadsheet with about ten cells. You plug in your coordinates and it instantly gives you the qibla. :-))
Note that with a model globe you could also do celestial navigation. If you see star A with a cenital distance C (complement of H above horizon) then you are located on a circumference with center at the geographical position of A and radius C. Just take a globe and do it. Unfortunately, for this to be of any practical use, the globe would have to be larger than your ship… which detracts from the practicality.
sailor, an azimuthal map centered on Mecca would, indeed, work. The key is thay you’re not looking at the line where it crosses Mecca, but where it crosses your current position. Radial lines from the center of an azimuthal map are the great circles, so the radial line from Mecca to your position on such a map would be the Great Circle path between you. Once you know the direction of that Great Circle at your point, you know the direction of Mecca. If you doubt this, get out a globe, some string, and an azimuthal map to Mecca (there’ve been a couple linked in this thread, I believe), and check it for a few locations.
Chronos, either you are mistaken or I am not understanding you. Can you explain further?
As I have explained, the great circle defined by your position and your destination (Mecca) changes azimuth continously and no two points have the same azimuth. An azimuthal map centered in Mecca gives you the azimuth from Mecca but from nowhere else.
OK, so you’ve got an Americanist who wants to pray towards Washington, and he’s in Mecca with this map. Right?
OK, you look at the green line you have on your map there-- That’s the Great Circle connecting the two cities. If you look along the Great Circle, you’re looking in the right direction. Cairo is also on that same Circle, so if you’re looking towards Cairo, you’re looking towards DC. The problem is now to find out how to find the direction to Cairo. Fortunately, though, Cairo is relatively close to Mecca, so you can get the direction to Cairo fairly easily from a standard projection, without too much distortion due to curvature.
If you’re still worried about that curvature distortion, choose some other landmark closer than Cairo for your bearing.
Chronos, if you read the previous posts you will see we have already discussed this. While, strictly speaking, the reasoning is sound, I do not consider that a solution to the problem for the following reasons:
You have merely changed the problem from “What is the azimuth from here to point X” to “What is the azimuth from here to a point that is closer than X”. The answer is that you still need to determine it and that it is not trivial. If a musmlim here in DC comes and says to me: “I need to say my prayers, would you kindly indicate to me the direction of Mecca?” and I answer “Oh, that is easy, it is the same direction as New York!” would you consider his question answered? I wouldn’t. He still has to find the azimuth of NY and, on top of that, I have introduced a certain error in the process.
I would not consider this to be a valid answer to the problem. You are just telling him another (inferior) way of resolving the problem. You are not resolving the problem.
You are saying “I can give you the azimuth of Mecca from DC by using an azimuthal map centered in Mecca (if I have another map of the DC area)” which is like the old saying: “If we had some eggs we could have some eggs and ham (if we had some ham)”.
The way I see it, the map centered on Mecca is a useful tool to bring with you if you don’t always know where you’re going to be. It’s not as accurate, and it requires additional maps, but it’s better than nothing. Were I a Muslem world traveller before the dawn of computers and such, I’d probably bring such a map with me. I could always pick up local maps as needed.
This would not be as good as having a map centered on my location, but would be several steps up from completely guessing. From what I recall, most Muslems don’t consder the prayers invalid if they happen to miss Mecca, so I’d imagine that this gives an accurate enough indicator for that. It may not be a valid solution to the problem, but it would be a tool that concievably Muslim travellers would have used.
Well, we are in agreement on how it would work. What we disagree is whether this can be considered a valid answer to the problem of determining qibla. I would say the reasonable answer is NO.
Suppose I am a muslim getting ready to travel to Caracas and want to know the azimuth of Mecca from Caracas.
My solution: Get an azimuthal map of the world centered in Caracas. End of problem.
Your solution: carry an azimuthal map centered in Mecca. This does not answer the question, it only translates it into another question (and may introduce a very large error in the process unless your map is of a huge scale). So, using the azimuthal map centered in Mecca I find another landmark which is much closer to where I am and is located on the same great circle (I insist this can introduce a substantial error). Now, It could happen that there are no landmarks on that line (sea or unmarked area) but let us further assume I find a convenient landmark… Now, all I have to do is go out and buy … an azimuthal map centered in my location but of a smaller scale! (A small scale map would serve as it preserves azimuth for all practical purposes). I have NOT resolved the problem, I have merely changed the scale of the problem and introduced an unacceptable error in the process.
I do not think it is reasonable to accept this as a valid answer/solution. If you ask me my age and I respond “I am 6 or 7 or 8 years older than my brother” I do not think I have answered your question, I have merely translated the problem to determining the same question about another person and introduced some error in the process.
To answer “what is the azimuth of Mecca?” with “the same as Pukeville” is not really answering the question at all. IMHO, of course.
Not to mention that anyone with a calculator with trig functions or a spreadsheet or a slide rule or a globe can determine qibla in a matter of seconds.
Since we seem to be through qibla’ing about map projections, I thought I’d interject a note on this. I have a little hand-held GPS unit used for hiking, which, of course, has a “goto landmark” function. Since I’m not in the habit of hiking to Mecca, or indeed, anyplace distant enough for question of whether the thing was computing a rhumb line or an azimuth to come up, I had to check this out. It computes an azimuth (based on either magnetic or true compass direction), and the correct great circle distance. I also now have a landmark in the thing for Mecca. Oddly enough, it comes with a fairly large number of prepackaged cities, and the list does not include Mecca.
I’m willing to bet that Magellan and Garmin have considered putting in a “qibla calculator” as a special function in some of their units, if they haven’t already.