Talk:Prime meridian

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Order of list of prime meridians[edit]

The list was once ordered by longitude, and recently changed to being lexicographically, by the name of the city etc. I have reverted it to what seems to me the natural order: by longitude.

When a category has an obvious order on its members, it is normal to use that order when listing it. For example, the article "perfect number" lists the first four perfect numbers "6, 28, 496, 8128". It does not list them in lexicographical order "28, 496, 6, 8128". And a list of monarchs of England since 1066 normally begins "William I, William II, Henry I, Stephen, ..."; I have never seen "Anne, Charles I, Charles II, Edward I, ...". Maproom (talk) 11:39, 20 December 2010 (UTC)

Map[edit]

Just double-checking as to why is French Guina colored blue on the map. If it is because the Prime Meridian runs through France, then why are the Falkan Islands and South Georgia and the South Sandwich Islands not also colored-in blue, is is it because they are only territories while French Guina is a region of France? —Preceding unsigned comment added by 216.96.155.229 (talk) 23:32, 25 April 2011 (UTC)

Yes, that's the reason. French Guiana is as much a part of France as Paris is. But the Falkland Islands are a dependency - belonging to, but not part of, the UK. Bazonka (talk) 07:54, 19 July 2011 (UTC)

Which Greenwich Meridian is Prime?[edit]

Until I read this article I did not realize how "off" our time and GPS meridian are from "The Prime Meridian" defined by the 1884 international agreement (not completely arbitrary) as passing through the observatory then in operation at Greenwich. I think that the article would be improved by editing out all the occurrences of "arbitrary" and simply insist that modern GPS and atomic clocks are off because the meridian has been mis-surveyed and the mis-surveys are now grandfathered in because there are too many maps to change. What's the use of an internationally agreed standard if it can be changed by 100 yards or more just because some early GPS system got off by that much? No wonder we end up bombing the wrong targets if our GPS is off by up to 100 yards. Dlw20070716 (talk) 02:55, 19 July 2011 (UTC)

It isn't just a matter of mis-surveying. If the people in charge of the early efforts at space-based geodesy had tried harder, perhaps by building a radio-telescope in Greenwich, the difference might be smaller than it is now. But the current prime meridian is based on an average of several different radio-observatories, all of which are moving with respect to each other due to continental drift. So the idea of basing the prime meridian on the location of a single observatory is obsolete. Jc3s5h (talk) 03:18, 19 July 2011 (UTC)

Dubious - arbitrary vs defined[edit]

The following sentence was tagged "dubious" by HTML2011 during his reorganization and split of the article:

The Prime Meridian is ultimately arbitrary unlike the parallels of latitude, which are defined by the rotational axis of the Earth with the Poles at 90° and the Equator at 0°.[dubious – discuss]

I see nothing dubious about that statement. Which of the two parts of the sentence is dubious? — Joe Kress (talk) 00:17, 29 March 2012 (UTC)

I also see nothing dubious there. The whole sentence is clearly true. Maproom (talk) 09:08, 29 March 2012 (UTC)
Perhaps better wording could be found. "Defined" and "arbitrary" are almost synonyms. The poles are an obvious choice due to the physics of the situation. The Prime Meridian is defined. It is arbitrary from a physics point of view, but not from a social point of view, or in view of the inventory of nautical charts (the original reason for the choice) and other intellectual property. Can anyone thing of a concise word or phrase for "strongly suggested by physics"?
To make the situation more complicated is that there are many kinds of poles, with corresponding meridians, such as ITRS, mean, true pole of date, and position of the pole on the surface of the Earth. Jc3s5h (talk) 12:03, 29 March 2012 (UTC)
I have replaced "defined" by "determined" - dos this help? Maproom (talk) 18:24, 29 March 2012 (UTC)
The lines of latitude are kind-of arbitrary, because there is no geographical or astronomical reason why there are 90 degrees from the equator to each pole. It is human convention that drives this. Bazonka (talk) 10:47, 30 March 2012 (UTC)
Perhaps this paragraph should only refer to the arbitrariness of the Prime Meridian vs. the geographically-defined Equator, removing the references to other lines of latitude. Bazonka (talk) 11:00, 30 March 2012 (UTC)
I have simplified the sentence, removing references to all lines of latitude except the equator. Bazonka (talk) 14:23, 1 April 2012 (UTC)
I still think the current sentence ("A prime meridian is ultimately arbitrary, unlike an equator, which is determined by the axis of rotation ...") is misleading. A prime meridian is a meridian so it must be terminated by the north and south poles, which means that it, too, is determined by the axis of rotation. I think this sentence should just be removed. Alternatively, how about this: "The choice of the 'prime' meridian is ultimately arbitrary, unlike like an equator, which must be at a latitude midway between the poles."? — Preceding unsigned comment added by 74.66.90.14 (talk) 04:16, 14 June 2014 (UTC)
Sounds good to me. --Lasunncty (talk) 00:14, 18 June 2014 (UTC)

Requested move[edit]

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: Move. Jafeluv (talk) 12:26, 9 April 2012 (UTC)


Prime MeridianPrime meridian – We don't capitalize generic terms. Dicklyon (talk) 05:23, 31 March 2012 (UTC)

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Merge IERS Reference Meridian into this article[edit]

Whilst this Prime Meridian article covers prime meridians on all planetary bodies, and alternative prime meridians on Earth, it is primarily about the most widely-used Prime Meridian on Earth, 0° longitude, running through Greenwich. This is what most people will expect to find when reading the article. The WP:COMMONNAME of the IERS Reference Meridian is "Prime Meridian" (particularly for non-specialists, i.e. the vast majority of readers of Wikipedia), and I can see no good reason why it has its own separate article. Its content would be much better held in the main Prime Meridian article, in particular the non-technical List of Places section. Bazonka (talk) 07:18, 6 April 2012 (UTC)

  • OPPOSE. Per Wikipedia:DAB#Broad-concept articles. The article is primarily about the concept named "prime meridian". The article has recently been moved from "Prime Meridian" to the generic name "Prime meridian". There are even several meridians at Greenwich. The common name of any prime meridian is prime meridian. That's why there are disambiguation pages in WP, because common names often are ambiguous. HTML2011 (talk) 02:26, 16 April 2012 (UTC)

Amended proposal - move[edit]

When I originally proposed this merge, this article was entitled "Prime Meridian". I agree that "prime meridian" is not the same thing as IERS Reference Meridian, but "Prime Meridian" is the common name for it. I now suggest moving IERS Reference Meridian to "Prime Meridian" (rather than it being a redirect to "prime meridian"), and place hatnotes into the two articles to link them together. (Maybe have a Prime meridian (disambiguation) article too.) See the discussion at Talk:IERS Reference Meridian. Bazonka (talk) 17:18, 16 April 2012 (UTC)

  • Oppose. The IERS reference meridian is not the only current prime meridian, and historically other meridians were the most important meridian of their eras. Jc3s5h (talk) 17:25, 16 April 2012 (UTC)
  • Oppose. Per Wikipedia:DAB#Broad-concept articles. Prime meridian is a broad concept. HTML2011 (talk) 05:11, 17 April 2012 (UTC)
  • Prime Meridian is ambiguous, even if you try to use the upper-case M to break that ambiguity; it doesn't really help. Leave it where it is, and make sure it's well linked from a hatnote in Prime meridian (where it's not, presently) and a disambig page, too, perhaps. Dicklyon (talk) 05:44, 17 April 2012 (UTC)
    • Hatnot may be fine. I am not a fan of these, but they do less harm than to have a topic under an ambiguous title. HTML2011 (talk) 17:47, 17 April 2012 (UTC)
    • I added a hatnote. HTML2011 (talk) 03:03, 20 April 2012 (UTC)
  • Even when referring to "the" Greenwich meridian, dictionaries use "prime meridian". The IERS uses "Reference Meridian" for the one(s) they define, and dictionaries don't mention that meridian. In the absence of any other sources commenting on whether to capitalize the one(s) defined by IERS, I would follow their usage. Jc3s5h (talk) 17:49, 14 June 2012 (UTC)

From pole to pole[edit]

I removed this section [1]:

  • it duplicates content found at IERS Reference Meridian
  • it was badly named, since it is a "List of places", called so at IERS Reference Meridian#List of places
  • the content does not belong here, since the page is about the general concept
  • this is meant to be an encyclopedia and not a coloring book where one can plaster any information anywhere

ChemTerm (talk) 21:59, 9 October 2012 (UTC)

I strongly disagree with the removal of this information. To answer your specific points:
  • Duplicate content. So what? The information is held in a template so there cannot be any discrepancy between the different places where it is shown. And if duplicate content is not allowed on Wikipedia, then why have templates at all? Content should be held where it is useful to the reader.
  • Badly named. OK, so rename it then. This is not a reason to delete.
  • The page is about the general concept. Yes, but think of the readers of Wikipedia, most of whom would not be experts in geodesy. What do you think they expect to find in the Prime meridian article? A schoolkid who is doing an assignment on the prime meridian, and is looking for a list of the countries through which it passes would probably look in this article before they went to IERS Reference Meridian, if they even get there at all. IERS is such a technical term that most users aren't going to look in that article, and by hiding useful information there, it does a disservice to Wikipedia. I agree that IERS Reference Meridian is a more precise name than the vague and unspecific "prime meridian" but surely WP:COMMONNAME carries a lot of weight in this regard. There are other prime meridians (including those on other planetary bodies) but the one commonly and currently used on Earth is many orders of magnitude more notable than any of the others. The inclusion of more information about this is not WP:UNDUE.
  • This is meant to be an encyclopedia. Exactly, so let's present information where people would expect to find it. This is relevant to the subject matter so it can hardly be described as just "any information". Bazonka (talk) 22:21, 9 October 2012 (UTC)

Referring to your last bullet point - and what readers expect is defined by User:Bazonka [2]? Please also not that you are engaging in edit warring. Your addition has be contested and removed. But you re-inserted it. ChemTerm (talk) 23:27, 9 October 2012 (UTC)

I don't really know how to respond to that. Your question isn't really a question so I don't understand what you're asking. I am fully aware of what edit warring is, and I know that I am within the limits defined by WP:3RR Bazonka (talk) 23:47, 9 October 2012 (UTC)
What is missing to make "What readers expect is defined by User:Bazonka?" a question? One of the Five Ws is there, a question mark is there, a verb is there, a subject is there. What is missing to make it a question for User:Bazonka? As for editing warring, do you understand WP:3RR "The rule is not an entitlement to revert a page a specific number of times."? ChemTerm (talk) 01:33, 10 October 2012 (UTC)
ChemTerm, it looks to me as though you are the one trying to change a stable article, so it is up to you to get consensus for your changes. Read WP:BRD for how the revision process works. And since it looks like it is actually you who is insisting your changes must stick, as if you have some kind of right to make them, it's quite likely that you will be the first one blocked for edit-warring. Franamax (talk) 02:16, 10 October 2012 (UTC)
@ChemTerm, most of your English seems good, so I'm surprised that you think that your sentence is a proper question. Having a W and a question mark doesn't necessarily make a question - you really just wrote a statement and put a question mark on the end. For example, "What ChemTerm means is unclear?" meets your criteria but it's not a question. I would answer you, but I really don't know what you're asking.
You also added a systemic bias template to the Earth section of the article, with the comment "why is the UK meridian first?". It seems ridiculous to query this as being biased. Why shouldn't the UK meridian be first? It is the one that is currently used (with minor variations, e.g. Greenwich and IERS) throughout the world as the prime meridian. It would seem silly to put text about the Paris Meridian (for example) at the top of the list, but not Greenwich/IERS. If you are suggesting that IERS should come ahead of Greenwich in the section, then just reorder it. Don't tag the section with silly templates. Bazonka (talk) 07:17, 10 October 2012 (UTC)

Zeroes in longitudes[edit]

I see that an editor has gone through the article removing zreoes from the longitudes, converting, for example,

Washington, D.C. 77°00′32.6″ W 

to

Washington, D.C. 77°32.6″W 

and

Greenwich 0° 00′ 05.33″ W 

to

Greenwich 5.33″W 

I find that this makes them harder to understand, so I have reverted the whole edit. Maproom (talk) 07:39, 1 February 2014 (UTC)

I agree that it's more readable with the zeroes. Also, on Prime meridian (Greenwich) (for example) the zeroes are still used: in the article but also in the gps coordinates. We should have one system for noting coordinates, not two. So I reverted the change again. Sander1453 (talk) 11:42, 1 February 2014 (UTC)

Lunar vs. Solar eclipses[edit]

The shadow cast on the moon would be seen at the same time in all places on earth. What must be meant is solar eclipses, since at different points on the earth the moon occludes sight of the sun at different times.AtomAnt (talk) 02:15, 5 January 2015 (UTC)

Yes, the shadow cast on the moon would be seen at the same time in all places on earth. So if one observed and recorded a full lunar eclipse at 1 AM in one country, and someone else recorded the same eclipse at 3 AM in another country, one would know the countries were separated by two hours, or 30 degrees of longitude. Jc3s5h (talk) 04:40, 5 January 2015 (UTC)
Actually, what the two astronomers/observers conclude first is that their clocks differ by two hours. Only if their clocks agree with their respective (true or mean) local times, measured using sun observations, they can then further conclude that they are separated by 30° of longitude. (BTW, to measure “times of lunar eclipses”, astronomers often agreed on a specific moon crater and measured the time when that crater disappeared in the shadow. This gives more exact results than measuring the time of a point of contact. Similarly, the true local time is best measured based on sunrise and sunset rather than on culmination of the sun.) -- David N. Jansen (talk) 23:16, 29 May 2016 (UTC)

New source[edit]

New to me, that is. Read German? See: Forstner, G. (2004); Längenfehler und Ausgangsmeridiane in alten Landkarten und Positionstabelle (dissertation), München, mainly p. 21-29. Online here. Sander1453 (talk) 08:46, 27 January 2015 (UTC)

Meridian of Bern[edit]

The value given (7° 26′ 22.5″ E) is the easting of the former astronomical observatory in Bern. This meridian was used in the Swiss coordinate system to link the projection and the coordinate system of national Swiss topographic maps (and data derived from them, e.g. cadastre entries in some cantons) with coordinates based on the Greenwich meridian. I do not know of any other use; so including this in the list of meridians is actually overstating, as the meridian of Bern was never used on maps with coordinates in something like “degrees east of Bern”. Eastings in degrees are given using the meridian of Greenwich (or, on the 1840 Dufour map, of Paris). It is a principal meridian for Switzerland, not a prime meridian.

I found this exact easting (and northing) on page 5 of the document linked as “Reference System CH” on this page of the Swiss Federal Office of Topography. (Note that in the meantime, the definitions have changed slightly; this is why the article “Swiss coordinate system” cites a slightly different meridian.)

No trace of the former observatory remains. On its site, in the 1960s the building for exact sciences (Exakte Wissenschaften, abbreviated ExWi) was erected. In one of its daylight courtyards, visible from my former office, was stona and a plaque indicating the centre of the former observatory. See e.g. [3] for an image (not suitable for inclusion in Wikipedia – written permission required). -- David N. Jansen (talk) 23:01, 29 May 2016 (UTC)

Changed column heading from "GPS longitude" to "Modern longitude"[edit]

I changed column heading in the table that lists historical prime meridians from "GPS longitude" to "Modern longitude". The edit that introduced the term "GPS longitude" is not accompanied by anything that would suggest that the editor researched each meridian and established that each and every one of them was a "GPS longitude". For some of these meridians it is probably impossible to determine where the meridian was with enough precision to distinguish any of the modern flavors of longitude.

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The documents.wolfram.com link is now at reference.wolfram.com. --Lasunncty (talk) 01:30, 25 May 2017 (UTC)