I once saw, in a museum, a compass-like pocket device for finding the Qibla. How do these things work?
-Ben
I’ve never seen one, but my guess is that it’s just a compass with an arrow pointing towards, say, north-east. It would only work in a limited area (say, Western U.S.) but that would still be reasonably useful. A universal Qibla indicator would need to know the latitude and longitude.
This looked a bit more complicated than that- IIRC it seemed to have a sundial-like part.
-Ben
Did it also have a clock of some sort on it? If it had a sundial, a clock, and a compass, then in principle, it had everything needed to determine Qibla from anywhere on Earth, but the user would probably still have to do some calculations on his own. With a GPS and a little bit of software, it could do it automatically, but then it probably wouldn’t look like a compass, and you probably wouldn’t have seen it in a museum.
Do you know when this device was made?
Chronos, I don’t get it. Can you expand? If I am at any given point on Earth, the azimuth of Mecca does not change with time. Why would looking at the sun be of any help? (Except at the very specific time of year when the GP of the sun is Mecca AND supposing I can see the sun from my posotion). In any case I cannot see way how a sundial and a magnetic needle can be of any help to determine the Qibla. Maybe you can explain?
It all depends on what information the user already has, and what information the device needs to provide. If we assume that the user knows where he is, all he needs is a map and a compass. With a map he can find out that Qibla is, say, 70 degrees from north. A magnetic compass can tell him which way north is, and hence the Qibla.
If he doesn’t know where he is, then the problem gets a lot more tricky. He would need to find latitude and longitude. The easiest way to find latitude is to measure the altitude of Polaris; this can be done with a sextant. Longitude is more difficult - you need an accurate clock and either a sextant or a sundial to find the exact time of transit (i.e. the time it reaches highest altitude) of a star or the sun. The tricky bit is that the clock must be set to the time of a known position, not local time. So you need to set the clock in Mecca or Greenwich and take it to your destination, and hope that the clock doesn’t drift by more than a few minutes during the trip. One minute offset would cause an error of about one mile.
scr4, your reasoning fails on several accounts. First off, I would say that if the devout muslim does not know where he is and is trying to find his location, then we have substantially redefined the problem to the point where it is an entirely different question. If we are going to accept that then we can say that first he needs to find a drugstore to buy reading glasses so he can see the compass. I do not think it is reasonable to assume the person does not know where he is in the world.
Secondly, a map does not give you the azimuth of Mecca or any other place due to the distortion of the projection. A globe yes, a map no. The only map that will give you the Azimuth to another place from your position is an azimutal map centered at your position and this means you have to know your position.
At any rate, if you are trying to find your position a sundial and a compass are about as useful as a teapot and a pair or scissors.
More useful would be 50 twenty dollar bills to buy a sextant, chronometer etc etc. I am well aware of how celestial navigation works. Check out this thread.
In short: if you know where you are a compass and sundial are pretty much useless to determine qibla and if you don’t know where you are… they are still useless.
Or can someone provide some convincing explanation to the contrary?
>> One minute offset would cause an error of about one mile.
Can you explain how you arrive at this figure? It is quite wrong.
First, a link to an azimuthal map centered on Mecca, for any interested:
http://www.timepalette.com/qiblamap.html
And a link to an article covering qibla indicators:
http://www.mhs.ox.ac.uk/sphaera/index.htm?issue7/articl7
From that link:
OK, did the device look http://www.agmgifts.co.uk/resources/astrolabe.html? That’s an astrolabe. A bunch of web sites (like this one) say that asrolabes were widely used for telling time and finding Qibla, but are vague on exactly how it’s done.
I could spend another half an hour looking for a detailed explanation, but it’s more fun to speculate. An astrolabe is usually disk shaped, and has a sighting device attached to the middle. You hang the astrolabe on a string, sight the sun or star, then read the markings on the disk to find the altitude of the sun or star (like this).
Also, you know those sliding disk things they sell at science museums? You rotate it so it indicates the current date and time, and the window shows what the current night sky looks like. Well, an astrolabe has exactly the same mechanism on it, so if you know the current location and time, it tells you the current position of various stars and the sun. Or if you know the position of the sun, you can calculate the current time.
In addition, I’d guess that on the back side of the astrolabe is written the direction of Qibla for every major city.
So, if the observer knows his current location and date, he can use the astrolabe to find the current time and Qibla.
Now, was such a device useful? I think it was. This is before the days of transatlantic voyages, so any traveller would know which city he’s closest to. No need for celestial navigation. I don’t think they had magnetic compasses or portable clocks though, so they would use the astrolabe to find the time and direction. The astrolabe is the equivalent of a combined map/compass/watch.
By the way, it’s easy to make a map which indicates Qibla for each location. You could play with various projection methods, or just draw arrows all over the map indicating Qibla for each location.
Sorry, forgot to preview… the first sentence was supposed to read “Did the device look like this?”
Sorry, that was a mistake - I had a feeling that didn’t sound right. One minute of arc (1/60 of a degree) on earth is one nautical mile, but of course the earth rotates much more than one minute of arc in a minute of time. Um, so the correct figure is 15 nautical miles, I think?
I would expect that by now there are electronic Qibla-finders available that incorporate GPS receivers, magnetic compasses, and charts of magnetic declination. If not, there’s a market awaiting.
scr4, I hope you enjoyed your speculating because it is all mostly mistaken. I won’t even bother going into details as you admit it is just speculation
You can take my word for it. If you know your location (if you are trying to find out your location that’s a different problem) all those items are pretty worthless. An azimutal map centered in Mecca is no good either. You need one centered at your position. A globe of the Earth would allow you to find Qibla easily. A flat map in general would not.
Asssuming you know your geographical coordinates and those of Mecca, the problem is simply resolving a trigonometric equation. It is basically the same problem navigators resolve to determine the computed azimuth of a celestial body.
given 3 numbers: latitude1, latitude2, Local Hour Angle (Longitude1 - Longitude 2), compute Azimuth and distance.
Two trig equations resolve this easily with a calculator. If anyone has any interest I’ll post the equations. I do not know if an astrolabe can resolve this graphically but I doubt it. I am familiar with the astrolabe and some of its uses but I cannot say I know everything about it.
I really don’t want to argue, but I would appreciate it if you could tell me what you find fault with my reasoning. I said it is speculation, but I provided a viable solution, and am convinced it is the only one. I haven’t seen you provide any viable theories.
If you followed the links I provided, they specifically said that astrolabes were used to find the time and direction for a prayer, often by travellers. The only possible interpretation is that the astrolabe was used to find the direction of north based on the direction of the sun or a star, and the current time based on the altitude of the sun or star.
Maybe I didn’t make it clear. As you said, you need trigonometric formulas to find Qibla for any given location. But the results can be tabulated and published, and even engraved on the back of an astrolabe - just a simple “In Constantinople, Qibla is 200 degrees from north”, etc. The astrolabe maker needs to make the calculation, not the user.
With such a table and the knowledge of where he is, the observer needs two additional pieces of information before he can do a proper prayer: current time, and direction of north. Both can be easily provided by an astrolabe. In fact, an astrolabe is the only way to measure those parameters, because there were no mechanical clocks or magnetic compasses back then.
[QOOTE]If anyone has any interest I’ll post the equations. I do not know if an astrolabe can resolve this graphically but I doubt it. I am familiar with the astrolabe and some of its uses but I cannot say I know everything about it.
[/QUOTE]
Then you should know that an astrolabe can calculate the position of a star given the date and time. Which means it can calculate the time given the position of a star. The astrolabe is just a replacement for a watch and a compass.
scr4, you are redefining the problem. It is one thing to say “I know where I am, where is north, what the time is and I want to find out the azimuth of Mecca” and a very different thing to say “I already know the azimuth of Mecca from my position but I do not know where North is”. I would not consider the latter as determining Qibla but as determining North.
I could also say that a pair of shoes would allow me to determine Qibla because they would allow me to walk to the mosque where it is marked. While the assertion is true it is misleading. Yes, you need a pair of shoes to determine qibla or to buy a hamburger.
The sites that you mention do not explain anything concrete and so it may be just a general assertion that the astrolabe and the astronomical information it provided were useful in a general way.
Anyway, it is not worth speculating about this. We keep redefining the problem to see if we can fit the solution into it. The Sundial and magnetic compass are useless in any case. A layman could not determine Qibla if given a magnetic compass, a sundial, an astrolabe etc. Better give him a pair of shoes so he can walk and find someone who can tell him.
As i have said, the problem is: Given Lat1, Lat2 and LHA determine azimuth. I would like to see a concrete explanation of how this could be done with an astrolabe. I am not saying it cannot be done, just that I’d like to see it. The sundial and compass would only be useful, like the shoes, in that you could sell them and buy a calculator.
Hey, if I had a really detailed azimuthal map centered on Mecca, I could use it to find qibla. I’d just mark off my spot, draw a line to the center (Mecca) and see the closest landmark that line intersected. From the map I posted, I can estimate that from where I am (upstate New York), qibla is approximately the same direction as Nova Scotia. With a normal map, I could then get the compass direction.
Here’s what Britannica has to say about the astrolabe, which is pretty thorough, but not entirely relevant. From what I can tell, mainly from the previous link I posted, the qibla indicator was a device used that simplified the calculation of the trigonometric function. I’m guessing that this would be possible to do in this manner. The astrolabe, on the other hand, seems to have been used for determining the time of day.
And another quote.
>> if I had a really detailed azimuthal map centered on Mecca, I could use it to find qibla
Nope, wrong answer. An azimthal map centered on Mecca gives the azimuth from Mecca to other places. It is no good for determining the azimuth from other places to Mecca. Think about it.
As I said, we have redifined the problem so many times any answer is good including this one: “The chicken”
But while we are at it we can chat about astrolabes. It is a shame my page about navigation instruments is not half baked yet. If I had not procrastinated so much I could just link to it. I cover all different navigation instruments in it, including the astrolabe.
Initially the astrolabe was just intended to observe and measure the height of a celestial body above the horizon. later it was combined with what we can call a circular slide rule or computer but this function is totally separate from the other and they could be separate instruments.
Resolving the spherical triangle using an astrolabe would be a PITA anyway
http://www.saundersandcooke.com/history.html
http://astrolabes.org
http://home.sunrise.ch/dbruno1/astrolabes/index.html
http://www.millersv.edu/~english/homepage/duncan/medfem/ast.html
shoot! I hit submit by mistake when I wasn’t half done. And I do know how to spell “redefined”.
Anyway, as you can see, doing any kind of calculation with the astrolabe is pretty complex and requires using different tympan for each latitude so the solutions are only very approximate. A $10 calculator will give you the solution with extrem precission and much easier. It is just that they didn’t have them 500 years ago.
I will post here a similar problem taken from the notes I gave my students when I taught great circle sailing:
Great Circle Nav. Practice problems:
Calculate great circle distance in NM and initial course
from Charleston SC (32°40'N, 79°55'W) to San Juan Puerto
Rico (18°24'N, 66° 5'W).
cos(D)= Sin(lat1) * Sin(lat2) + cos(lat1) * cos(lat2) * cos(lon2 - lon1)
Sin(lat1) = 0.539751
Sin(lat2) = 0.315649
cos(lat1) = 0.841825
cos(lat2) = 0.948876
cos(lon2 - lon1) = 0.970995
cos(D)= 0.539751 * 0.315649 + 0.841825 * 0.948876 * 0.970995 = 0.9459904
D = arc cos (0.9459904) = 18° 55'0 = 1135 NM
Sin(lon2-lon1)
Tan(Z) = --------------------------------------------------
sin(lat1) * cos(lon2-lon1) - cos(lat1) * tan(lat2)
Sin(lon2-lon1) = -0.239098
sin(lat1) = 0.539751
cos(lon2-lon1) = 0.970996
cos(lat1) = 0.841825
tan(lat2) = 0.332656
Tan(Z) = -0.979956 and Z = -44.4
Sign(sin(-44.4)) = minus Sign(Sin(lon2-lon1)) = minus
Zn= 180 + Z = 180 - 44.4 = 135.6
Similar problems with their solutions:
LAT.LAT. LON.LON. DIST. Init.Course
DEG.MIN. DEG.MIN. NM Z Zn
CHARLESTON SC 32° 40'N 79° 55'W
SAN JUAN PR 18° 24'N 66° 5'W 1135.0 -44.4 135.6
LISBON 38° 30'N 9° 22'W 3170.5 55.2 55.2
ST. JOHNS 47° 0'N 52° 0'W 1920.6 -60.6 299.4
CAPE TOWN 33° 30'S 20° 35'E 6210.0 -54.9 125.1
HONG KONG 22° 0'N 113° 0'E 6230.9 72.6 72.6
NEW DELHI 28° 0'N 77° 0'E 1983.1 -72.1 287.9
SINGAPORE 0° 51'N 103° 44'E 2238.1 -47.9 132.1
You can use the same formulas to resolve any similar problem between any two places. That is what a computer does to generate an azimuthal map: it calculates distance and direction for thousands of places.