History UsefulNotes / TheLongitudeProblem

* The drama/documentary ''Longitude'' (see Literature above) is all about this problem; it mentions the "sympathetic magic" thing, together with other crackpot schemes like having dozens of ships anchored at fixed longitudes to provide reference points. Even after John Harrison builds several accurate chronometers, he finds himself opposed by {{Obstructive Bureaucrat}}s who prefer the lunar method.

* When you have two clocks or watches it's very easy to figure out your longitude when one is set to a reference time and the other is set to the local time.

For more details, see Wiki/TheOtherWiki, [[http://en.wikipedia.org/wiki/History_of_longitude here]].

* In the ''Franchise/{{Tintin}}'' album ''[[Recap/TintinRedRackhamsTreasure Red Rackham's Treasure]]'', the protagonists originally thought that the coordinates on Francis Haddock's parchments had the Greenwich meridian as the prime meridian. Tintin correctly figures that the French naval officers under UsefulNotes/LouisXIV were using the Paris meridian as their reference point. [[spoiler:Although they do find the shipwreck, the treasure was actually taken by Haddoque.]]

# Have a very accurate clock. If you carry around a clock set to some fixed time, you can compare local time to time at that fixed location, and thereby determine how different your longitude is from its longitude. On the other hand, constructing a clock that keeps good time while on a moving ship is itself a very difficult problem. The first chronometer capable of keeping sufficiently accurate time while on a ship was made by John Harrison in 1761; for quite some [[IncrediblyLamePun time]], nobody actually believed that a mere [[ItWillNeverCatchOn clock]] could solve the problem astronomers had struggled with for centuries[[note]]mainly because nobody believed that the clock ''that'' accurate could be made capable of withstanding the rough conditions of the ship[[/note]] - and even once people did listen, they were prohibitively expensive for years - but eventually they became cheap enough to be the standard method of determining longitude.

[[Real Life]]

* In the ''Franchise/{{Tintin}}'' album ''[[Recap/TintinRedRackhamsTreasure Red Rackham's Treasure]]'', the protagonists originally thought that the coordinates on Francis Haddock's parchments had the Greenwich meridian as the prime meridian. Tintin correctly figures that the French naval officers under UsefulNotes/LouisXIV were using the Paris meridian as their reference point.

* ''The Island of the Day Before'' by Creator/UmbertoEco contains a number of different attempts to solve the longitude problem, including one that uses SympatheticMagic. The theory is that a wounded dog is taken on the ship; the sympathetic magic is performed on the dog every night at midnight in Paris; by watching the dog's reaction and noting the local time, you can figure out your longitude much as with the "clock" method.

For more details, see TheOtherWiki, [[http://en.wikipedia.org/wiki/History_of_longitude here]].

* In ''Mutiny on the Bounty'', Roger Byam gets a posting as a midshipman on the ''Bounty'' despite having no sailing experience thanks to his father's work on determining longitude.

* In ''Film/TheBounty'', Fletcher Christian's inability to determine how far away Pitcairn Island is (because he can't get a fix on longitude) nearly causes his crew to mutiny for a second time before they finally reach the island.

* In ''[[Literature/TheBountyTrilogy Mutiny on the Bounty]]'', Roger Byam gets a posting as a midshipman on the ''Bounty'' despite having no sailing experience thanks to his father's work on determining longitude.

* ''The Medici Emerald'' by Martin Woodhouse and Robert Ross has LeonardoDaVinci investigate the death of a friend of his, a merchant captain renowned for getting where he wanted to go at unheard-of speed. The captain had done a favor for an Arab mathematician who built a very accurate clock ... in the 1460s or '70s.

* ''Literature/GulliversTravels'': When he's in Laputa fantasizing about what he could do if he were immortal, one of the problems he imagines being able to solve is "the discovery of the longitude". He meant, of course, the ''quick'' discovery. Discovering longitude on land wasn't a major problem in hos time — sure, it required several careful astronomic observations and complicated calculations, but with some time it could be done very precisely. Sailors simply hadn't the time to do so, because their ship would certainly change its place between observations, and they needed a quick, even if somewhat less precise, way of figuring the longitude, instead of a very precise one that took a week to complete.

The moons of Jupiter eclipse behind their primary very regularly and very frequently, making this method fairly easy to use; it was used to find the longitudes of places on land more or less from the time Galileo discovered them and the pattern of their eclipses, which helped greatly in the development of accurate maps of landmasses (including coasts). Unfortunately, finding the moons on the deck of a moving ship proved to incredibly impractical.\\

# Have a very accurate clock. If you carry around a clock set to some fixed time, you can compare local time to time at that fixed location, and thereby determine how different your longitude is from its longitude. On the other hand, constructing a clock that keeps good time while on a moving ship is itself a very difficult problem. The first chronometer capable of keeping sufficiently accurate time while on a ship was made by John Harrison in 1761; for quite some [[IncrediblyLamePun time]], nobody actually believed that a mere [[ItWillNeverCatchOn clock]] could solve the problem astronomers had struggled with for centuries[[note]]mainly because nobody believed that the clock ''that'' accurate could be made capable of withstanding the rough conditions of the ship[[/note]], and even once people did listen they were prohibitively expensive for years, but eventually they became cheap enough to be the standard method of determining longitude.

Measuring the angular distances of the Moon to the fixed stars--or the Sun, when they're both up--was much easier to do, requiring only equipment that all seamen already had (i.e. a sextant and a compass), particularly when using the Sun (big giant thing in the sky that it is, seamen preferred to use it). However, this measurement was completely useless on its own. The method relies on the fact that the Moon's path across the sky moves very regularly (half a degree per hour), and that the Moon's position relative to the fixed stars is the same no matter where you're looking from. Thus, you can tell what time it is in a fixed location (e.g. in London)...if an astronomer has already done the maths and published a table predicting the position of the Moon as observed from London for each hour of each day of that year. A daunting task. And then the navigator would have to do a bit more maths to actually use the tables properly. Despite all the work it took, this method was standard from the late 18th through the early 19th century, and for the early period of chronometers (see below), this method was often used to make slight corrections to the clock.

# Observe celestial phenomena which vary rapidly and are visible simultaneously worldwide, and compare local time when you see it to the predicted time of occurrence at a fixed location. There were two ways of doing this: observing the eclipses of the moons of Jupiter or observing the angular distance from the Moon to some particular star: \\

The moons of Jupiter eclipse behind their primary very regularly and very frequently, making this method fairly easy to use; it was used to find the longitudes of places on land more or less from the time Galileo discovered them and the pattern of their eclipses. Unfortunately, finding the moons on the deck of a moving ship proved to incredibly impractical.\\

On the other hand, figuring out how far east or west you are is considerably more difficult, because of the rotation of the earth. If you want to determine your longitude, you have to contend with the fact that, if you're observing something in the sky now, someone several hundred miles to your east could have observed almost precisely the same thing an hour ago. On the other hand, the rotation does have an advantage: if you know what time it is in some fixed location, and know what time it is locally, you can tell how far you are east or west of that fixed location. Prior to a genuine solution, the general practice was to sail to the correct latitude then go East or West until you hit land, but that has certain drawbacks: not only is it remarkably inefficient, it makes it difficult to avoid any nautical hazards that are at the same latitude as your desired destination.

Neither of these methods were viable until the middle of the 18th century; thus, any ships out of sight of land before that time would have had no good way of knowing where they were, leading to many navigational mishaps as well as wasted time at sea. For the British, this problem became intolerable and led to a massive 20,000 pound reward (on the order of ten million of today's dollars). The money was enough for an entire generation of bright minds to seek a solution.

Another kind of "longitude problem" that may show up as a plot device in works of fiction (as in the {{Tintin}} example below) is the fact that, for centuries, there was no universally accepted prime meridian (a meridian arbitrarily defined as the zero longitude meridian). Various conventions have been used or advocated in different regions and throughout history. Therefore, longitude coordinates that you find in old texts can be tricky if there is no mention of the prime meridian used. You could be mistaken if you infer that it was the Greenwich meridian.

* ''The Island of the Day Before'' by Creator/UmbertoEco contains a number of different attempts to solve the longitude problem, including one that uses SympatheticMagic (the theory is that a wounded dog is taken on the ship; the sympathetic magic is performed on the dog every night at midnight in Paris; by watching the dog's reaction and noting the local time, you can figure out your longitude much as with the "clock" method).

** Adapted into a television mini-series staring Michael Gambon as Harrison, shown on A&E in North America, and Channel 4 in the UK.

* In ''Ut mine Stromtid'', a 19th-century novel set in a small town in Mecklenburg and written in a mix of High and Low German by Fritz Reuter, there is a sequence during the Revolution of 1848 where a man enjoys himself by pretending to read out "new" (which he in fact made up) to the simple townfolk. One of the stories he regales them with is that of a rebellion breaking out the Canary island of Ferro (El Hierro) because of the threatened abolition of the [[https://en.wikipedia.org/wiki/Ferro_Meridian Ferro Meridian]] (which was the meridian most commonly used in continental Europe until the late 19th century).