Talk:Longitude

message: I am curious, however about all the fuss with clocks.  Yes, clocks are great and solve the longitude problem. I have taught that.  But the motion of the Moon in relation to the Sun and to the stars can be used to tell time, too.  Just occurred to me that though it's a bit complicated and not quite so accurate, it might work to low accuracy, but good enough for simple navigation, say within a few degrees longitude.
Pdn 05:19, 25 Feb 2005 (UTC)
replies: text: If you're not using clocks and only using astronomical objects to find your location, you're doing astronomy instead of navigation.  After measuring angles to the Sun, Moon, and stars, you then have to go solve simultaneous equations to find at what time all those objects are at those locations (unless you have astronomical location-time tables) and at what location all the angles match your readings.  Moon rise alone doesn't tell you where you are if you don't know the time.  If you know what time moonrise was at Greenwich and you know your time you can compare the two times.  If you don't know the time then you have to measure at least one other thing which varies on a useful time scale (the movement of Venus is fast enough that you might be able to figure out within several days what the difference is between you and a standard, while the rise time of Rigel changes slowly enough that you might have to watch it for months in order to have enough data to compare it to moonrise and find your location).  If you have a chronometer with only a minute and second hand then you'd be able to compare times between events and get better data than only comparing relative angles.  -- SEWilco (talk) 15:19, 25 February 2008 (UTC)
replies: text:  Navigation is navigation regardless of how it's done; it doesn't become astronomy just because you are measuring the positions of celestial objects.  As far as solely using celestial objects for navigation, see Lunar distance method. --Michael Daly (talk) 17:38, 25 February 2008 (UTC)
replies: text:  You're right.  I was actually referring to the amount and type of work needed rather than the purpose.  With no timekeeping instrument the task of locating one's position is much more difficult.  I've considered astronomical navigation methods on the past, and although they can be used in some situations (primary requirements are suitable measuring tools and being able to wait while getting enough data), a clock and accurate astronomical info greatly reduce the location effort.  Having only astronomical info generally requires using that to solve for the local time/position of the Earth.  The Lunar distance method depends upon an astronomer having earlier calculated all the necessary tables based upon the astronomer's clock.  I was referring to the mentioned problem of calculations from the motion of astronomical objects.  -- SEWilco (talk) 17:54, 25 February 2008 (UTC)
replies: text:  A clock is not dependant on good weather and visibility a thousand miles out at sea. Try shooting a star in a howling gale and pouring rain with the ship rising and falling in time with your stomach. Add to that the possibility that your estimated position may be off by several tens of miles and that you risk running onto rocks, with the loss of your ship and yourself. Then see which method you prefer. Finding your longitude at sea is a serious business when your life literally depends on it. Second best won't do. See here: Scilly naval disaster of 1707  — Preceding unsigned comment added by 80.7.147.13 (talk) 18:32, 18 November 2013 (UTC)
thread_title:  Fuss with clocks 

message: Moon/Mars picture/text problem: While the diagram of the moon and Mars shows how they would not appear to be lined up from a position to the west, it shows the Moon appearing to the east of Mars, while the text describes Mars as being to the east.  Where's the error, and should this be explained?Piledhigheranddeeper (talk) 19:04, 9 December 2008 (UTC)
thread_title:  History 

message: Latitude says that they are not "exactly" equal to 1 nautical mile whereas this article says that Latitude is "exactly" equal to 1 nortical mile! This seems to be to be something that needs clearing up. —Preceding unsigned comment added by 58.105.29.26 (talk • contribs) 
: The latitude statement that one minute of latitude is very close to one nautical mile is correct for the reasons it states. Nevertheless, a minute of latitude was indeed originally exactly one nautical mile at the time it was defined, when it was thought that the Earth was a perfect sphere (rather than an oblate spheroid with an undulating geoid). — Joe Kress 01:17, 16 June 2006 (UTC)
replies: text: The same thing happened with the original definition of the meter; when they discovered that the Earth wasn't a perfect sphere after all, adjustments had to be made. Piledhigheranddeeper (talk) 19:11, 9 December 2008 (UTC)
thread_title:  Discrepancy between this and Latitude 

message: I think the article should emphasize the primary purpose of longitude: that together with the latitude it uniquely identifies any point on the surface of Earth (or other celestial body).  This is mentioned only in the third paragraph, saying
: A specific longitude may then be combined with a specific latitude to give a precise position on the Earth's surface.
and in the link to Geographic coordinate system in the See also section.  I am not sure yet how to change the article to emphasize this more, so I did not edit it.  – b_jonas 21:08, 19 June 2006 (UTC)
thread_title:  Coordinate system 

message: How many miles is 15 degrees (1 timezone) of longitude? --HomfrogTell me a story! 00:41, 30 December 2006 (UTC)
replies: text: A time zone is similar the section of an orange—it is fat at the equator and slims down to a point at either pole, so its width varies from 1670 km (1037 statute miles) at the equator to 0 km at the poles. Mathematically, 15° of longitude = (1669.800 + 5.595sin²φ)cosφ km, where φ is the latitude, varying from 0° to 90°. Multiply by 0.621 for statute (land) miles, and by 0.540 for nautical miles. Technically, each time zone is a gore, 24 of which can be combined to form a flat world map which can be cut so that it can be glued onto a sphere to create a globe, covering the entire sphere without any gaps or overlaps. The fattest part of a gore touches both neighbors at the equator even when lying flat, but their points all touch at the poles when glued onto a sphere. An example of such a world map/globe with only twelve gores (rather than 24) is here. — Joe Kress 21:19, 31 December 2006 (UTC)
replies: text:  You might want to work that explanation into globe, and link to it from gore. Andy Mabbett 00:45, 17 March 2007 (UTC)
thread_title:  Mile conversion 

message: There are very few dates given in this section. I wanted to know when Harrison built his various chronometers, when the Longitude Prize was offered, when the voyages occurred, etc. Could someone with access to reference materials please provide them? --Sapphire Wyvern 01:50, 9 August 2007 (UTC)
replies: text: All such info was moved to History of longitude and the details on Harrison's chronometers remain in John Harrison.  --Michael Daly 19:15, 5 November 2007 (UTC)
thread_title:  Lack of dates in the "Longitude Act and Harrison's chronometer" 

message: Could someone add information on why degrees are divided into "minutes" and "seconds"?  Is there some relation to time that I am missing or is 60 simply a useful number to divide from hence a clock analogy?  —Preceding unsigned comment added by 142.179.217.154 (talk) 00:13, 8 September 2007 (UTC)
replies: text: Degrees were (and are) the basic division of a circle.  Each degree was then divided into 60 minute portions.  Then each minute was divided a second time to yield seconds.  At least that's what my geometry teacher taught us. Piledhigheranddeeper (talk) 19:19, 9 December 2008 (UTC)
thread_title:  Minutes and Seconds? 

message: As per previous comments above, I've split out the history section and merged it with similar history sections in several other articles.  This is now a single article History of longitude.  --Michael Daly 19:07, 30 October 2007 (UTC)
thread_title:  History of longitude created - history section removed. 

message: IPA would be helpful.  —Preceding unsigned comment added by 81.140.57.113 (talk) 16:38, 27 February 2008 (UTC)
replies: text: Done and thanks, because I found I have always pronounced it wrong. I said  instead of . −Woodstone (talk) 20:11, 27 February 2008 (UTC)
replies: text:  You weren't wrong. The OED gives both, but I've never heard the dʒ version. I think it's an americanism. Algebraist 23:59, 27 March 2008 (UTC)
replies: text:  Not really.  The /g/ pronunciation is a relatively recent British innovation; the /dʒ/ was the original pronunciation and is still the only one found in the US, while it appears to be losing ground in the UK.  — Preceding unsigned comment added by 82.61.82.166 (talk) 21:28, 22 September 2014 (UTC)
thread_title:  pronunciation 

message: As of today there is an article on every whole-numbered line of longitude with the exception of the following (all are West longitude lines): 124, 126, 127, 128, 129, 131, 132, 133, 134, 136, 137, 138, 139, 142, 143, 144, 146, 147, 148, 149, 151, 152, 153, 154, 156, 157, 158, 159, 161, 162, 163, 164, 166, 167, 168, 169, 171, 172, and 173. Backspace (talk) 20:49, 3 February 2009 (UTC)
thread_title:  Currently existing articles 

message: Gavin Menzies' 1421 book is used as a reference for the Chinese initial discovery of a longitude method. I'm not an expert, hence writing this before editing the article, but I know the book is widely discredited by historians (read any account of it other than by Menzies himself) and at any rate is popular historical fiction and not a scholarly work. I cannot find any other reference suggesting the Chinese had discovered a method for locating longitude before the Europeans, I propose the whole paragraph be deleted. 82.1.124.153 (talk) 13:31, 26 August 2012 (UTC)
replies: text: Removed - I agree with your reasoning. Wizzy…☎ 15:02, 26 August 2012 (UTC)
thread_title:  Gavin Menzies reference in 'history of' section 

message: “… it is with the help of these clocks and the following methods that longitude is found. … observe exactly the time at the place from which we are making our journey. … When we have completed a journey … wait until the hand of the clock exactly touches the point of an hour and, at the same moment by means of an astrolabe … find out the time of the place we now find ourselves. … In this way I would be able to find the longitude of places, even if I was dragged off unawares across a thousand miles. … it must be a very finely made clock which does not vary with change of air.” – Regnier Gemma Frisius  1553
In an era where the relationship between the 24 hour system in tandem with the Lat/Long system organized around the Earth's rotational characteristics are disputed,it is no accident that this insight of Frisius is airbrushed out.Orion216 (talk) 07:57, 29 October 2013 (UTC)
thread_title:  Disgraceful omission 

message: In the table, it would appear that the tables for latitude and longitude are transposed? Cinderella157 (talk) 05:37, 10 November 2015 (UTC)
thread_title:  Table 

message: I believe "longitude" is also used for the location of a body on an orbit (e.g. position of a planet at a given moment).
Certainly it is also used in "longitude of the ascending node", one of the constants used to describe an orbit. (Which is using a different frame of reference, afaik, than the above concept.)
The lead should reflect these common generalized uses of the geometrical concept of longitude, instead of limiting the definition to "the east–west position of a point on the Earth's surface", as the article currently does.
--BjKa (talk) 14:20, 7 November 2018 (UTC)
replies: text: Found this: Ecliptic coordinate system#Spherical coordinates --BjKa (talk) 14:33, 7 November 2018 (UTC)
thread_title:  Celestial Mechanics 

message: This section seems somewhat unbalanced. The first sentence states that longitude is important both for cartography and navigation, then what follows talks almost entirely about navigation. Also the time-frame is very limited. There is a long history of ancient work on longitude, from the Greek astronemers throuhgh the Muslim and Hindu worlds and back to mediaeval Europe that is not mentioned, and also much after Harrison, with electric and wireless telegraphic methods. The diagram on lunar distances is misleading - all that can really be seen, in exaggerated form, is parallax - but parallax is a source of error that has to be allowed for in the calculation, not what is primarily being measured. I suggest following the outline of the History of Longitude article, condensing it to about the same length as the current section (about 1,000 words). Comments appreciated. Kognos (talk) 11:50, 21 September 2020 (UTC)
replies: text: I've added the revised section. There are no images yet, I will add these. Kognos (talk) 17:35, 26 September 2020 (UTC)
thread_title:  History