# Any navigators? Error on Jeopardy tonight? **URL:** \ **Category:** Factual Questions\ **Created:** [October 8, 2004, 12:14am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122 "2004-10-08T00:14:12Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [October 8, 2004, 12:14am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/1 "2004-10-08T00:14:12Z")
On _Jeopardy!_ tonight there was a clue in a category “Long” Jump (i.e. the question has to include “long”), something like, “You use a sextant to determine this.” The “correct” response was “longitude.” But was it correct? I’m no navigator, but I’ve read Dava Sobel’s “Longitude” and other books about the longitude problem, and it was my understanding that a sextant measures the angle of an object above the horizon. With this you can determine latitude. (This is verified by [this site.](http://www.wordiq.com/definition/Sextant)) But to measure longitude you need to compare local time with the time at a known location, e.g. Greenwich. I don’t think a sextant will help you do that. Am I missing something? Can you use a sextant to determine longitude, or was _Jeopardy!_ wrong tonight? ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [October 8, 2004, 12:32am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/2 "2004-10-08T00:32:26Z")
IIRC, you need to measure the angle of the sun to determine local noon, so a sextant is used for both longitude _and_ latitude. ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [October 8, 2004, 12:32am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/3 "2004-10-08T00:32:56Z")
You use the sextant to shoot the sun and determine exactly when local noon occurs. You compare the moment of local noon with the time at Greenwich, and thus determine longitude. The trick was building a clock to carry Greenwich time with you accurately. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [October 8, 2004, 12:53am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/4 "2004-10-08T00:53:33Z")
Okay, but it’s the clock that tells you the longitude, not the sextant, right? I mean, you could just as easily say you use a pencil to determine longitude. Necessary, but not sufficient. I suppose a lot would depend on how they worded the clue, but I think the spirit of the thing is mistaken. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [October 8, 2004, 1:09am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/5 "2004-10-08T01:09:12Z")
I think you are right in the sense that a sextant is pretty much sufficient to measure latitude, but the clock is also needed for longitude. Yet because an observation with the sextant is necessary to calculate latitude (the chronometer alone won’t do it), and because they gave the “long” clue, I think we can give Jeopardy! a pass on this one. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [October 8, 2004, 3:18am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/6 "2004-10-08T03:18:25Z")
> [@commasense](#): > > Okay, but it’s the clock that tells you the longitude, not the sextant, right? I mean, you could just as easily say you use a pencil to determine longitude. Necessary, but not sufficient. How would you determine local noon without a sextant? Eyeballing it? For every minute you’re off, that’s a 15 mile error. I’m not sure I could eyeball local noon to better than 20 minutes. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [October 8, 2004, 5:01am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/7 "2004-10-08T05:01:46Z")
Use your GPS? The point being that with a sextant _only_, you can only measure latitude. In that sense, the clue is misleading at best, and wrong at worst. I think they were just looking for another “long” clue, and got sloppy. I only comment on it because it’s so rare for them to make mistakes like this. ---
**Author:** ![squeegee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squeegee/32/14537_2.png) [@squeegee](https://boards.straightdope.com/u/squeegee)\ **Post date:** [October 8, 2004, 5:42am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/8 "2004-10-08T05:42:43Z")
> [@CurtC](#): > > How would you determine local noon without a sextant? Eyeballing it? For every minute you’re off, that’s a 15 mile error. I’m not sure I could eyeball local noon to better than 20 minutes. Stand on a steady (non-moving) surface, draw a line northward using a compass. Place a stick at the base of the line. When the sun’s shadow on the stick intersects that line, it’s noon local. Of course, this requires a magnetic compass – is this allowed? If not, here’s a method that doesn’t require a compass: Site the position of the sun at sunrise and sunset. The halfway point between those two positions is due south (in the northern hemisphere). Mark off a line of any distance towards that vector, and your starting point is due north. Follow directions above to determine local noon. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [October 8, 2004, 6:54am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/9 "2004-10-08T06:54:26Z")
> [@commasense](#): > > Use your GPS? > > The point being that with a sextant _only_, you can only measure latitude. In that sense, the clue is misleading at best, and wrong at worst. I think they were just looking for another “long” clue, and got sloppy. > > I only comment on it because it’s so rare for them to make mistakes like this. Actually the sextant is used to measures angles above the horizon. If you use the angle of the North Star above the horizon to get latitude you need tables of the angle from the north pole of Polaris at the time of day you make the measurement. The actual north pole is about one degree away from Polaris and a one degree difference in latitude is 60 nautical miles. I’m not a navigator but I’m pretty sure that with the proper ephemris for the sun you can also get latitude from the sun angle above the horizon at noon. It was a poor question. The sextant alone will get neither an acurate latitude nor longitude. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [October 8, 2004, 6:55am UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/10 "2004-10-08T06:55:37Z")
In addition to not being acurate it won’t be accurate either. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [October 8, 2004, 3:50pm UTC](https://boards.straightdope.com/t/any-navigators-error-on-jeopardy-tonight/268122/11 "2004-10-08T15:50:40Z")
> [@commasense](#): > > Okay, but it’s the clock that tells you the longitude, not the sextant, right? I mean, you could just as easily say you use a pencil to determine longitude. Necessary, but not sufficient. > > I suppose a lot would depend on how they worded the clue, but I think the spirit of the thing is mistaken. If it was worded the way you say, in the OP, then I don’t think the spirit of the thing is mistaken. Nor was it sloppy. Jeopardy clues are clues, not definitions. Your analogy is flawed too. A pencil is obviously not necessary in your example.