Talk:IERS Reference Meridian

Requested move

 * 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: Not moved. Jafeluv (talk) 06:17, 24 April 2012 (UTC)

IERS Reference Meridian → Prime Meridian – Prime Meridian is the WP:COMMONNAME for this meridian. It is highly likely that most people searching for "prime meridian" are actually interested in the IERS Reference Meridian - this is the commonly used meridian on Earth. But the IERS name is not commonly used, except in very technical contexts. The existing article prime meridian contains generic details of what a prime meridian is, on Earth and on other planetary bodies, listing different ones that are, or have been, used. I am not proposing that this article be moved or renamed. Hatnotes or a dab page should link the two together. As an alternative to moving this article, it could be merged into prime meridian. Perhaps Greenwich meridian should also be merged. Bazonka (talk) 17:17, 16 April 2012 (UTC)


 * Oppose – this "common name" is far too ambiguous to use for a specific prime meridian. A hatnote link from Prime meridian is in order, though. Dicklyon (talk) 05:45, 17 April 2012 (UTC)
 * Oppose - "prime meridian" is a name for a general concept. Hatnote added. HTML2011 (talk) 03:05, 20 April 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.

Edit Request
A new paper REFUTES the INCORRECT claim, made in the "Location" section that:"The 5.3-arcsecond shift is a legacy of the first satellite navigation system, the Doppler based TRANSIT system." This paper is freely available - for abstract see http://link.springer.com/article/10.1007/s00190-015-0844-y. I will not repeat the conclusions of that paper other than to state that the shift is a result of the Deflection of the Vertical (DoV) (which I don't really understand). The authors of that (peer reviewed) paper explicitly refute the above claim; clear and strong evidence that it is WRONG. This article required correction.173.189.72.141 (talk) 15:52, 11 August 2015 (UTC)


 * Thanks for pointing out this article; I've made the edit. Jc3s5h 23:59, 17 August 2015 (UTC)


 * Thanks indeed. Other media have reported on this, making things easier for non-scientific editors ;-) Sander1453 (talk) 11:10, 22 August 2015 (UTC)

IRM Definition
The article is currently lacking a clear-complete-exact definition of the location of the IRM. Because the IRM is now rather virtual-technical (instead of being referenced to any current real spot on the earth surface), it may be too complicated etc to give an exact definition? Still, it would be good if knowledgeable folk would try...

The article states "IRM is the weighted average of the reference meridians of the hundreds of ground stations" but that seems over-simplified -- at the least, the IRM seems offset by some amount from this average? Offset by how much? When/how was this determined? Does the offset vary -- due to what? It goes on to say "stations' coordinates are adjusted annually". We are left with the clear-as-mud impression that all kinds of fudging are involved in these calculations, and we are left with no clear understanding of the basic concept at the root of defining an IRM in the context of the whole surface of the planet shifting around. I'm afraid we need a worked example of each tectonic plate shifting and rotation of specific amounts from one year to the next, and how the IRM location would then be determined.

Perhaps the whole technical discussion is only concerned with describing how the IRM location shifts over time, as opposed to where it was located to begin with. Leaving us wondering when in time and where in space the reference beginning was. Since there is an offset-error from Airy transit circle, that does not seem to be the exact origin -- yet the origin seems to somehow be connected/derived from that exact location, in some complicated way?

I am left disappointed, to not be able to find the exact story of how the reference-zero meridian for all world locations came to be located exactly wherever it is today. -71.174.190.122 (talk) 19:59, 22 December 2016 (UTC)
 * It would also be nice to understand why it is not going through the observatory in Greenwich? OK, the new one is a plane that goes through the center of mass of the earth (which is a mathematical point), possibly also defined by the axis of rotation? Would make sense, because otherwise the longitude+latitude north and south poles would rotate around the real poles. I assume the center of mass is exactly on this axis. It simply has to. So what defines this IRM plane? Only a line (north to south through the center of mass). But this in fact doesn't define anything. Because you could still make the plane go through any point on the surface of the earth. Be it Greenwich, Greenland, a sandwich in Paris or the most important city on the planet. So why is it 100+odd meters away from Greenwich?--TeakHoken213.150.228.38 (talk) 13:37, 15 June 2020 (UTC)
 * See https://www.iers.org/IERS/EN/Science/ITRS/ITRS.html
 * There are a variety of observation stations spread around the world which constitute the International Terrestrial Reference Frame. Each site may be equipped with sophisticated instruments, such as a radio telescope. These are assigned positions which are periodically updated so there is no net rotation. That is, the reference meridian, on average, stays in the same position with respect to all the stations. But since the tectonic plate that carries the Royal Greenwich Observatory is moving, and only some of the ITRF stations are located on that plate, on average, the position of the Royal Greenwich Observatory in the ITRF system moves.
 * The current position of the ITRF reference meridian came about through many decisions over many decades about how to move from various older systems to a succession of newer systems. In each case, the choice was to make the improved system match the immediate predecessor. These decisions accumulated to yield the present difference. Jc3s5h (talk) 14:39, 15 June 2020 (UTC)
 * It's my opinion that you are meant to be disappointed.
 * The entire object of the miserable exercise was to remove the perfectly good terms like GMT and Greenwich Prime Meridian in favor of long, hard to remember acronyms as a form of the relentless assault on history. The truth is that the FAGS changed this, probably because the French were never happy that the Prime Meridian went through Greenwich and not Paris. And the FAGS were mostly French.  Remember, going all the way back - they were the only one of 41 nations not voting for Greenwich as the international standard in 1884, instead abstaining.
 * The clear tone of the authors of the article is that somehow the original specification got it wrong. But, obviously, for an arbitrary thing like the prime meridian there is not right or wrong.  It could just as easily been anywhere else. Here's what the article says:
 * "The predominant factor for the 5.3 arcsecond offset between the Prime meridian (IERS Reference Meridian, shortly called IRM) and the Prime meridian (Greenwich) is that the former takes local gravity into account, so it is slightly out of step with the system validated by star observation (including but not limited to the sun). In the IRM Prime Meridian system, precisely timed "clock star" observations are used, such as the Prime Meridian vertical, a local vertical, which for decades entailed a fine spider's web thread scale within the optical assembly.[3]
 * This is clearly nonsense. It's like saying Zero has to be redefined as 0.00001 or something.  More precise ways of measuring something do not require moving the origin of the system.  So why was it really moved?  It wasn't moved due to failing to take "local gravity into account".   One could just as easily have taken local gravity into account and kept the prime meridian right where it was.
 * International Earth Rotation and Reference Systems Service is the body responsible for maintaining Time Standards. For some reason they had to put their imprint on location, and what better way than to capture the Prime Meridian away from its historic name and rename it after their bureaucratic organization.  Oh, yeah, and move it just enough to justify the change, about 100 meters. Clearly they could not come up with enough mumbo-jumbo to drive it all the way to Paris, but making Greenwhich obsolete was enough of a victory for the FAGS.
 * IERS, we learn, was established in 1987, and replaced the Bureau International de l'Heure, abbreviated BIH. We also learn that "From 1956 until 1987 the BIH was part of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS)". The switch from the historic location of Greenwich to new one a football field over happened in 1984. "This was officially accepted by the Bureau International de l'Heure (BIH) in 1984 via its BTS84 (BIH Terrestrial System) that later became WGS84 (World Geodetic System 1984) and the various ITRFs (International Terrestrial Reference Systems)."
 * The hated "Greenwich Prime" was moved an arbitrary amount to the Left, the name replaced with a ugly acronym, the history of the overwhelming Royal British contribution to navigation blunted. The year gives us the final clue: Greenwich adopted over French objections by 40 of 41 nations attending a conference in 1884, Greenwich meridian moved a little (they got it wrong! It should have been over here the whole time!) and renamed to a meaningless acronym: 1984. It took 100 years, but eventually the prime was wrestled away from those overbearing Brits. Toasts with the good champagne at all the French academies on that occassion!
 * (But no, I'm just kidding and being cynical. Politics has NOTHING to do with science.  This was all done for legitimate scientific reasons. just like the article kinda/sorta explains.) ZeroXero (talk) 20:17, 2 January 2022 (UTC)

The map should be updated.
When one tries to click on the map to see more precisely where the Prime Meridian is, the larger map does not contain it. This is weird if you look at the article for the 180th meridian the map has the meridian nicely drawn on it. I have no idea how what is done here was even done, but the "blow up" lacks the meridian, which is the topic of the article, and the reason one would like to see the larger map. In other words: total fail. 2601:1C2:4C00:E7F:611B:2646:F190:3301 (talk) 19:13, 2 January 2022 (UTC)

Contested capitalization
Changes to capitalization by are contested at Wikipedia talk:Manual of Style/Capital letters. Jc3s5h (talk) 18:45, 28 December 2022 (UTC)