Talk:Prime meridian

Changed column heading from "GPS longitude" to "Modern longitude"

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.

what is the east to west meridian ?

what is the east to west meridian ?

The lines on a globe that run east to west are called parallels of latitude. The 0° parallel is the equator. Jc3s5h (talk) 03:04, 11 August 2018 (UTC)

Longitude of Cadiz

The longitude of Cadiz depends on the part of the city it passes through. Cadiz is an island in the Bay of Cadiz about one mile from the mainland that trends NNW-SSE. The modern city occupies the entire island, about 3.5 miles long. The old city occupied only the westernmost mile of it. The longitude of the nearest observatory is 6°12'19", the Real Instituto y Observatorio de la Armada in San Fernando on the Isla de León, essentially part of the mainland, about six miles southeast of the old city. The central longitude of the modern city is near 6°17', near the most recent longitude in the article, 6°17'15". The previous stable longitude was 6°17'40", passing through the eastern half of the old city. The central longitude of the old city is near 6°18'. The longitude of the Universidad de Cadiz near the western shore of the old city is near 6°18'13". The Castillo de Santa Catalina is an old fort on the western or Atlantic shore of the old city with a longitude of 6°18'29". Another old fort is Castillo de San Sebastian on a tiny island near 6°18'49" only 2000 feet southwest of the old city. Which is the better longitude? — Joe Kress (talk) 04:05, 9 November 2018 (UTC)

The original longitude of Cadiz was added 12:58, 23 December 2016‎ by 83.43.241.182 stating that it was used by the "Spanish Army and other countries during a century", at first calling it the "Cadiz (Spain) Meridian" then calling it the "San Fernando Meridian (Cádiz, Spain)" in successive edit summaries. His source was the Spanish version (cited in the article) of this English source, "In search of the lost meridian of Cadiz", El País, 2016-12-23. The referenced study is by Miguel Ramos, who said the meridian was used from 1753 to 1850. In 1753 the Navy’s Astronomical Observatory was established inside the city’s Castillo de la Villa, no longer in existence, whose longitude became this lost Cadiz meridian. It was located on the south coast of the old city, described in both cited articles in terms of landmarks. Without more research, the original editor's longitude of 6°17'40" is good enough to keep it in the article. I have no idea why he called it the San Fernando Meridian which is far to the east, 6°12'19" as stated above. — Joe Kress (talk) 15:09, 9 November 2018 (UTC)

The Castillo de la Villa (long since replaced by another building) was located north of Av. Campo del Sur (built on landfill south of the original south shore), just west of Calle San Juan de Dios, just south of Calle Meson, and just east of Calle Silencio. All of these streets are described as its former borders in the Spanish Wikipedia Castillo de la Villa. Its central latitude was 36° 17' 42", and its central longitude was 6° 17' 35". I am replacing the article's 6° 17' 40" with the latter. — Joe Kress (talk) 17:13, 9 November 2018 (UTC)

The latitude is wrong, and tenths of an arcsecond need to be added to both to properly position where they cross in the center of the building. Thus 36° 31' 42.2" N, 6° 17' 35.5" W. The northern and southern facades of the original fort had 25-meter long walls between towers, and the eastern facade's wall was 53 meters between towers. Although the western facade was the longest, no dimension is given. — Joe Kress (talk)

Incomplete citation

The section "Prime meridian at Greenwich" contains the following citation: "Greenwich Observatory ... the story of Britain's oldest scientific institution, the Royal Observatory at Greenwich and Herstmonceux, 1675–1975 p.10. Taylor & Francis, 1975" This is incomplete. The work is in fact in three volumes by separate authors: Greenwich Observatory. The Royal Observatory at Greenwich and Herstmonceux, I675-1975. Volume i: Origins and Early History (I675-1835). By Eric G. Forbes. Volume ii: Recent History (1836-1975). By A. J. Meadows. Volume iii: The Buildings and Instruments. By Derek Howse. London: Taylor & Francis, I975. It looks as though the relevant volume is ii, but it would be good to check. Does anyone have access to this work? It's not in any of the libraries I use. If not, I can find an alternative source for this. Kognos (talk) 20:11, 27 September 2020 (UTC)

List of prime meridians: can there be more than one?

The table lists many meridians but I thought that by definition there can only be one 'Prime' meridian, the one established by international convention – that's what makes it prime. So what makes the others 'prime'? Are they not just 'reference' meridians? The table needs an intro and the comments column needs some text in every row as well as a citation, surely? --John Maynard Friedman (talk) 17:53, 4 December 2020 (UTC)

The first definition at lexico.com is

A planet's meridian adopted as the zero of longitude.

Before the international conference in Washington, each nation tended to adopt its own. Even today, there are different ones for different purposes, although all the modern ones tend to be within a few hundred meters of each other. Jc3s5h (talk) 17:58, 4 December 2020 (UTC)

Yes, I knew about the Meridian of Paris, which was the main competitor to Greenwich. I guess what I am really saying is that the information in the table is so sparse that I can't tell whether these meridians are genuinely historic or more recent (and possibly OR/spoof additions. If the table had an intro to say something like "prior to the wossname International Conference in which the Greenwich meridian was formally adopted as the worldwide standard prime meridian, many countries defined their own prime meridian as given in the table below." or something like that. I didn't realise how little I know! --John Maynard Friedman (talk) 01:16, 5 December 2020 (UTC)

Era naming consistency

The history section uses both CE (common era) and AD (anno domini). There doesn't appear to be any contextual case for using the different naming conventions. One or the other should be used. Lanceleasure (talk) 14:10, 30 July 2021 (UTC)

@Lanceleasure: Per MOS:ERA, the one first used must be retained. You raised the question, which means you have to fix it. :-D

It looks like the first use was diff=532860633&oldid=532838638 on 13 January 2013 by Chris55, who used the religious notation. --John Maynard Friedman (talk) 16:47, 30 July 2021 (UTC)

In fact, when I put that there, there was a single use of the CE notation in the table of meridians, which was the main content of the article at the time, under Ujjain, which I probably didn't notice. The current first paragraph of the history, the only other use of the CE notation, was inserted on 21 Oct 2020 by an IP with this edit diff=984595645&oldid=979745129.

MOS:ERA actually states "An article's established era style should not be changed without reasons specific to its content" and it's certainly arguable that the 7 uses of the religious notation have set the established style, quite apart from the fact that the current first paragraph in the History section is out of chronological order and would be more appropriate after Eratosthenes and Ptolemy.

I'm open to consensus on this issue. The first paragraph should probably be moved anyway. Chris55 (talk) 17:44, 30 July 2021 (UTC)

Further on the Hindu calculation in the first paragraph: I've read the reference by Schmidt and it says nothing about the calculation or significance of longitude, only the use of latitude. I don't know more of the Surya Siddhanta than in the Wiki article but that article also doesn't refer to longitude. Chris55 (talk) 16:46, 31 July 2021 (UTC)

Sorry but sauce for the goose etc. The first use was CE, there is no reason intrinsic to the topic to say why we should use one rather than the other, so your edits (however inadvertent) changed the established era style and it is they that must be changed to use CE. I'm afraid your argument reduces to WP:ILIKEIT. The Manual of Style policy exists because this is an issue where consensus is impossible: the perspectives are irreconcilable. --John Maynard Friedman (talk) 18:57, 31 July 2021 (UTC)