Talk:Prime Meridian

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So why did San Domingo vote against the siting of the Prime Meridian in Greenwich? Anybody know what their alternative was? Lisiate 01:23 24 Jul 2003 (UTC)

We need a public-domain map on this page, showing where this line is.

Last text version of Prime Meridian version: "The meridian (line of longitude) passing through Royal Greenwich Observatory, Greenwich, England is the prime meridian (longitude = 0 degrees).

The meridian was agreed upon in October 1884. At the behest of the President of the United States of America, 41 delegates from 25 nations met in Washington, DC, USA for the International Meridian Conference.

At the conference the following important principles were established:

1) It was desirable to adopt a single world meridian to replace the numerous ones already in existence. 2) The Meridian passing through the principal Transit Instrument at the Observatory at Greenwich was to be the 'initial meridian'. 3) That all longitude would be calculated both east and west from this meridian up to 180°. 4) All countries would adopt a universal day. 5) The universal day would be a Mean Solar Day, beginning at the mean midnight at Greenwich and counted on a 24-hour clock. 6) That nautical and astronomical days everywhere would begin at mean midnight. 7) All technical studies to regulate and extend the application of the decimal system to the division of time and space would be supported.

Resolution 2, fixing the meridian at Greenwich, was passed 22-1 (San Domingo voted against), France and Brazil abstained."

---

The previous version declared that Rome meridian corresponds to 1° 30' 28" east of Greenwich, which is obviously nonsense. I have corrected it to 12° 27' 08.04", which is what I have in my sources, but I do not have any authoritative reference; if someone does and it contains some other value, please make a correction. --Mormegil 19:16, 11 Oct 2004 (UTC)

I've just thought of something. What if plate tectonics aren't entirely equal with every plate respective to every other.. wouldn't england move a bit, screwing up the prime meridian's placement??

You are correct. The prime meridian was defined to be where Airy's transit instrument was in 1884, but a different system is now used. Furthermore, the Royal Greenwich Observatory is now a museum, with no working instruments. The prime meridian is now defined relative to the International Terrestrial Reference System, which uses extragalactic radio and visible sources to which the rotating Earth is referenced via Very Long Baseline Interferometry and other methods. In particular, it is defined to have no net rotation regarding horizontal tectonic motions over the whole earth. — Joe Kress 19:12, Mar 17, 2005 (UTC)

Come on, Britain hasn't moved 100 metres since 1884!!! Lee M

The writer was correct when noting that "England moved a bit", a few centimeters, not 100 meters. Nevertheless, the Prime Meridian has apparently moved about 100 meters because it is no longer tied to the Royal Observatory at Greenwich nor any specific point on land—it is now tied to a geometric figure, an ellipsoid. The Prime Meridian used to be defined via the observatory's transit circle which was mounted in a vertical plane (via a plumb bob), which is perpendicular to sea level around the island of Great Britain. But sea level undulates by ±100 meters world-wide, meaning that the longitudes of other observatories were not referred to Greenwich, even though that was their intent. To correct this mess, a single ellipsoid was selected to coincide with the average world-wide sea level. A perpendicular to this world-wide ellipsoid at its own Prime Meridian now appears to intersect land about 100 meters east of the old transit circle. — Joe Kress 07:31, 16 January 2006 (UTC)

I still don't see why the new Prime Meridian couldn't have been adjusted to coincide with the old one. Lee M 11:27, 24 January 2006 (UTC)

You have a point. According to the official explanation, they tried to adjust it to match, but could not because there no working instruments at Greenwich when the single reference ellipsoid was selected. — Joe Kress 09:09, 25 January 2006 (UTC)

Which is the real prime meridian? The one marked in Greenwich or the one according to GPS recievers/Google earth?(AndrewAnorak (talk) 09:22, 12 December 2007 (UTC))

Changed Oslo to Kristiania. That was the name of the city when the local meridian was in use. Ulflarsen 18:42, 17 Mar 2005 (UTC)

I have copies from Norwegian maps (from U.S. Library of Congress) which say "Oslo meridian". As the stub at Kristiania says, that name applied from 1878-1924; as this article says, Greenwich was agreed on as the universal prime meridian in 1884. So it would only have been Kristiania for about a six-year period; most of the time when this was used, it would have been Oslo. BTW, I did find the coordinates and will add them too. Gene Nygaard 19:31, 17 Mar 2005 (UTC)

Well, okay, I caught myself--I should have known better. So it was "Christiania" rather than "Kristiania" from 1624 to 1878. Nonetheless, it is "Oslo" which I have seen on maps. I changed it to Oslo (Kristiania) and am not going to worry about the Chr- spelling, people should be able to figure that much out themselves. Gene Nygaard 19:41, 17 Mar 2005 (UTC)

Simply because the Greenwich meridian was adopted in 1884 does not mean that all local meridians suddenly ceased to exist. The Washington meridian itself was not repealed until 1912 (the borders of several western states were defined relative to it even after 1884). It was actually used for astronomical purposes until 1950 alongside the Greenwich meridian (see the American Ephemeris and Nautical Almanac). The Paris meridian has a very long history -- it was retained until 1911, and then Greenwich mean time was defined as Paris Mean Time retarded by 9 min 21 sec. Many small countries did not repeal their local meridians until much later, and some may still exist. Nepal used that of Katmandu until the 1990s and may still use it. — Joe Kress 02:42, Mar 18, 2005 (UTC)

If days start at midnight at the International Dateline, the very first hour of each day should start at the same International Dateline, not at the Prime Meridian. Even in Britain, when we consider train and airplane schedules, we should refer to a 24 hour day, starting at the first time zone of the world, located within the International Dateline (180 degrees longitude) and the 165 degrees East Meridian. To consider another way to measure 24 hour days is useless and nonsense. Even more, the Prime Meridian should not be used to divide Earth's surface into an Eastern and a Western Hemispheres. Longitude meridians should start at the International Dateline and progress westerly 360 degrees around the Equator. This way nobody should need to calculate progression of Easter Longitude backwards from the Prime Meridian, since movement of "apparent" Sun is always from East to West. Besides this, Time Zones is a mathematical concept, but English language lacks the use of another concept: Legal Time, which is in spanish-speaking countries, the time fixed by governments to rule national activities in the whole country. And these "Legal Time Zones" maybe, or maybe not, coincident with mathematical Time Zones, according to the reasons each country has to base its own decision. --Fev 17:42, 22 January 2006 (UTC)fev. And the International Dateline, or 180 degrees longitude meridian, should be included as another reference meridian since it is the line where every solar day starts. --Fev 18:53, 31 January 2006 (UTC)

Contents 1 International Dateline 2 Vandalism 3 Distance corresponding to degree of longitude 4 Queen Maud Land 5 Mecca?

[edit] International Dateline

I think Franey's contribution on reverting "gibberish" is a very poor one and lacks scientific support. My own contribution was made to improve this article, not to erase "gibberish" (and this article is full of it). At least, Franey should discuss my contribution before reverting it, in the same way I did in the page of discussion. --Fev 06:34, 19 February 2006 (UTC)

• The International Date Line is not a meridian. It is a wiggly line that follows the 180° line of longitude for maybe 60% of its length; the rest of it swings roughly between 170° E and 170° W. (Calling this "a few exceptions" is an interesting choice of words.)
• No time zone starts at the Greenwich Meridian; nor is any time zone bound by the IDL and the 165° E line of longitude. The Greenwich Meridian marks the theoretical centre of the GMT zone, which nominally lies between 7° 30' W and 7° 30' E; similarly, the +/-12 zone extends in theory from 172° 30' E to 172° 30' W.
• "the first hour of each day must start at the International Dateline": please explain how a measure of time can be said to start at a particular place.
• "Train and airplane schedules (even in Britain) follow a 24 hour a day system": what has this got to do with anything?
• "the reference meridian can not be considered at the Greenwich Meridian, but the 180° longitude": are you suggesting that cartographers, mariners, aviators, armed forces, GPS satellites, and everyone and everything else that uses geographic co-ordinates should drop a system established internationally for over a hundred years and start measuring longitude from somewhere else?

— Franey 17:07, 20 February 2006 (UTC)

This was my reference to the International Date Line considered by Franey as gibberish and, therefore, reverted:

“After the International Dateline was fixed to the 180° longitude (with a few exceptions) to start every day at midnight, there is no longer need to use the Greenwich Meridian as a starting line for identifying Time Zones, since the first Time Zone must be the one lying between the International Dateline and the 165° degree meridian E of Greenwich. Of course, none of the above reference meridians has as much importance as the International Dateline and that is why this line should be considered as the most important reference meridian now: since each day starts at midnight at the 180° longitude, also the first hour of each day must start at the International Dateline. Train and airplane schedules (even in Britain) follow a 24 hour a day system, and the reference meridian can not be considered at the Greenwich Meridian, but the 180° longitude”.

Fortunately, Franey introduced some comments on the text included above and I am trying to explain now my viewpoint:

• Franey: The International Date Line is not a meridian. It is a wiggly line that follows the 180° line of longitude for maybe 60% of its length; the rest of it swings roughly between 170° E and 170° W. (Calling this "a few exceptions" is an interesting choice of words.)

My commentary: “The 180th meridian …., conveniently passes almost entirely through ocean” (read article, please) must be another “interesting choice of words”. And “this line (180th meridian) is used as the basis for the International Date Line”, “with some modifications” (see article again) must be another “interesting choice of words”. Even more, the International Date Line “is” at the 180th Meridian, since these “modifications” were made by governments from several islands and countries to avoid having different dates within their territories. Remember what the article says: “conveniently passes almost entirely through ocean”. Why to use the word “conveniently”?. Because if there were no land along the 180th Meridian, both lines (180th Meridian and the International Date Line) would be the same line.

• Franey: No time zone starts at the Greenwich Meridian; nor is any time zone bound by the IDL and the 165° E line of longitude. The Greenwich Meridian marks the theoretical centre of the GMT zone, which nominally lies between 7° 30' W and 7° 30' E; similarly, the +/-12 zone extends in theory from 172° 30' E to 172° 30' W.

My commentary: You are right in this, except that the error is in the way of considering Time Zones both sides of the meridian of reference of every one of them, and this is not your error. Let see: the +/-12 zone extends in theory from 172° 30' E to 172° 30' W. Why to say “in theory”?. This is what actually happens. And the very problem is in naming this Time Zone “+/-12 zone”, because it is the same thing that saying: “this zone has 7 and a half degrees of longitude both in the western and Eastern hemispheres”. So, the eastern part of this zone (at the western hemisphere) would have a certain date and the western part (at the Eastern Hemisphere, which is a kind of paradox) would be the following day. What I proposed is that measure of time must follow the apparent Sun because there is no way in thinking another way to consider time. This means that when is 12 noon at a given meridian (say, the Prime Meridian) starts the first hour in the afternoon towards the west and this very first afternoon hour will end, obviously, when the Sun reaches the 15th degree west of the Prime Meridian, just at the very same moment when it is 1 o’clock p.m. at the Prime Meridian. But the way it is wrongly established looks like if the Sun, after reaching the Prime Meridian, “goes back” to the East 7 and a half degrees longitude. Or, the other way around, if every meridian is at the very centre of the Time Zone where it is located, there would not be a Time Zone between two contiguous time zone meridians, but two halves of two different time zones and, consequently, would be the same thing as if every meridian would indicate noon at 12:30 in the afternoon.

The article says: Universal Time is notionally based on the WGS84 meridian. However, the standard international time UTC can be discrepant from the observed time on the meridian by up to about one second, because of changes in the earth's rotation. This corresponds to a variation in longitude of roughly 300 metres either way at Greenwich.

My commentary: It is not “variation in longitude of roughly 300 metres” but variation in time. To say it the opposite way, is nonsense. This is almost the same error in saying that “a minor earthquake in Greenwich could change longitudes throughout the world” (a short text fortunately reverted) since meridians of longitude are virtual lines and consequences of a minor earthquake in Greenwich would not be virtual, but real. So, an earthquake in Greenwich would not change longitudes throughout the world even the sophisticated apparatus used to determine longitudes in Greenwich (or wherever would be sited) went crazy.

Franey states: "the first hour of each day must start at the International Dateline": please explain how a measure of time can be said to start at a particular place.

My commentary: “Universal Time is notionally based on the WGS84 meridian” (see article). I could not say it better.

• Franey said: "Train and airplane schedules (even in Britain) follow a 24 hour a day system": what has this got to do with anything?

Elementary, my dear Franey: a 24 hour a day system is equivalent to a daily system. This means that if Universal Time is based on the WGS84 meridian (as the article says), when is Saturday midnight at this meridian, starts a new day (Sunday) throughout the world. Right?. Completely wrong, since Sunday (the very same Sunday) started 12 hours ago at the International Date Line.

My commentary: “the reference meridian can not be considered at the Greenwich Meridian, but the 180° longitude”

Of course, especially to measure Time, both UTC, GMT and Time Zones.

• Franey's: “are you suggesting that cartographers, mariners, aviators, armed forces, GPS satellites, and everyone and everything else that uses geographic co-ordinates should drop a system established internationally for over a hundred years and start measuring longitude from somewhere else?”.

I am not suggesting it: I am saying the whole world already dropped that system since everybody uses now a 24 hour (or daily) system, which starts at the 180th meridian towards the west at 12 midnight everyday. --Fev 03:59, 22 February 2006 (UTC)

[edit] Vandalism

I deleted the word 'weenie' from "The Greenwich weenie". I presume this is mindless vandalism - I could not see any other meaning... MacAuslan 06:43, 3 October 2006 (UTC)

That vandalism was by 69.123.109.138. Immediately before it, the entire first paragraph and all images were deleted by Terry wonghk. If you monitor an article ("Watch this page") on a regular basis, then you can identify such vandalism via "Compare selected versions" in "Page history" by comparing the last version you know to be good with the latest version. See Wikipedia:Vandalism. — Joe Kress 05:03, 4 October 2006 (UTC)

[edit] Distance corresponding to degree of longitude

I added the word "approximately" to this. The expression given is actually a good approximation to WGS-84, with a maximum relative error of 8.8e-6. The exact expression is a*cos(phi)/sqr(1-e^2*sin(phi)^2), where a is the equatorial radius, 6378137 m; e^2 is the square of the eccentricity; sqr() is the square-root; the caret denotes exponentiation; and (1-e^2) = (1-f)^2, where f is the flattening, 1/298.257223563.

[edit] Queen Maud Land

The article currently says that the prime meridian runs through the Norwegian part of Antarctica, called Queen Maud Land. I see two issues:

• It appears that Norway's claim is not officially recognized except by a few countries. Wikipedia should not list the land as part of Norway, except perhaps with an explicit note that this is a disputed claim.
• Do people call that region Queen Maud Land, even if they deny Norway's claim to it? If so, then we can use the name without mentioning Norway.

And of course we should back up whatever we do with reliable sources. Joshua R. Davis (talk) 15:42, 2 March 2008 (UTC)

Who, besides the USA and Russia, does not recognise it? All the countries that have claims in Antarctica recognise it; the non-recognition of those who don't is just sour grapes. The Antarctic Treaty freezes (pun intended) the status quo ante, which was that those who were actually there had claims and those who came late didn't, but were entitled to say they didn't recognise the earlier claims, so long as they didn't actually do anything about that non-recognition. -- Zsero (talk) 16:59, 2 March 2008 (UTC)

The Queen Maud Land article mentions only four countries that have officially recognized Norway's claim, and the Antarctic Treaty System article says that the treaty does not recognize any claims to territory whatsoever (Article 4). Are those articles inaccurate? I'm honestly asking; I'm no expert.

It is obvious that the Prime Meridian runs through Antarctica. For the article to make the more specific claim that it runs through Norway, we need to cite a source, it seems to me. Joshua R. Davis (talk) 17:27, 2 March 2008 (UTC)

Those are the countries that have territories there, so it's their recognition that's important. The treaty simply leaves things as they were; it neither recognises nor negates the pre-existing claims, it just prevents anyone from making new claims or trying to conquer existing claims. -- Zsero (talk) 19:05, 2 March 2008 (UTC)

I don't understand. What about Argentina and Chile? Do they recognize that Norway possesses that part of Antarctica? Would they agree with you that only the opinions of Australia, France, New Zealand and the UK are important?

When it comes to potentially contentious topics, such as biographies of living persons and territorial boundaries between countries, we need to be especially careful, to make sure that Wikipedia contains only verifiable statements.

How about this solution: We take out the flags (which don't serve any serious purpose anyway) and describe the antarctic part of the Prime Meridian as running through Queen Maud Land, which is claimed by Norway? Joshua R. Davis (talk) 20:59, 2 March 2008 (UTC)

Argentina and Chile don't recognise these claims, because nobody at all recognises their claims. But if the line went through a disputed area we'd probably want to stay neutral. In this case, though, the area it goes through isn't disputed. There's only one claimant, and a few countries that came too late to stake claims putting fingers in their ears and singing, while agreeing to do nothing to change the status quo ante.

In any case, you're right that the flags don't add anything, and we could drop them with no loss of information. No need to note that QML is claimed by Norway either. Just put Queen Maud Land, and anyone interested in learning more about it can follow the link. -- Zsero (talk) 21:30, 2 March 2008 (UTC)

[edit] Mecca?

When was Mecca used as a Prime Meridian? Is there a source for this? (We should probably find cites for all the meridians listed, but I'm particularly skeptical about this one, because Maimonides, writing at the height of the Arab dominance of the sciences, used a Prime Meridian 20° east of Mecca. Had Mecca been the standard used by Arab geographers at the time, Maimonides might have been reluctant to follow suit, but it would have made sense for him to substitute Jerusalem, not a neutral spot far to the east.) -- Zsero (talk) 05:28, 28 April 2008 (UTC)