tag:blogger.com,1999:blog-4228590560998272503.post4543834373844188908..comments2024-03-10T08:20:29.607+00:00Comments on GEOBLOGY: Something’s happening to Magnetic North in Great Britain in 2014 by Susan MacmillanAnonymoushttp://www.blogger.com/profile/05297797356322244437noreply@blogger.comBlogger12125tag:blogger.com,1999:blog-4228590560998272503.post-78947659233622494512014-05-01T05:44:02.876+01:002014-05-01T05:44:02.876+01:00This comment has been removed by a blog administrator.21cssIndiahttps://www.blogger.com/profile/10783846365727856945noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-864495044075783682014-02-12T13:08:20.955+00:002014-02-12T13:08:20.955+00:00Hill-walkers are using maps with grid north lines ...Hill-walkers are using maps with grid north lines so yes, what matters is whether grid magnetic angle, rather than declination, is easterly or westerly. Declination is important for mariners using sea charts, where the north lines are true north lines i.e. lines of equal longitude. <br /><br />For topographic mapping in Great Britain using the transverse Mercator projection (the basis of the British National Grid), along 2 degree W longitude, true north and grid north are in the same direction. West of this, true north is east of grid north and east of this, true north is to the west of grid north. There's a useful, though rather detailed, document available from the Ordnance Survey at http://www.ordnancesurvey.co.uk/docs/support/guide-coordinate-systems-great-britain.pdf describing the coordinate systems in Great Britain and I find Figure 8 handy for visualizing the relationship between grid north and true north. The angle between grid north and true north is called grid convergence and, if you're really keen, can be computed using a spreadsheet available at http://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-net/coordinate-spreadsheet.html. <br /><br />Till now magnetic north has been west of both for the whole country but over the next few years will slowly become east of grid north and west of true north for the area west of 2 degrees W. After about 2018 and for the area east of 2 degrees W, magnetic north will slowly become east of true north but remain west of grid north for a while, and eventually for the whole country, will be east of both. But for hill-walkers using compasses it is the relationship between grid north and magnetic north that is important. True north can generally be ignored, unless doing very accurate night navigation using the pole star!<br /><br />Thank you for your interest.BGS Geomagnetismhttps://www.blogger.com/profile/00582120463256218907noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-84443680002747830532014-02-11T17:58:15.210+00:002014-02-11T17:58:15.210+00:00So, actually for the hill walkers of the country w...So, actually for the hill walkers of the country what counts is if you have easterly or westerly grid magnetic angle and not easterly or westerly declination (east or west from true north, where true north coincides with the line of longitude 2oW). Meaning that if the magnetic north is west of grid north but still east of true north, we need to change the old mnemonics in order to navigate with map and compass. <br /><br />Is that true?<br /><br />thank you for your timeAnonymoushttps://www.blogger.com/profile/14073963724476846380noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-25960354805719890962014-02-11T17:23:00.864+00:002014-02-11T17:23:00.864+00:00This comment has been removed by the author.Anonymoushttps://www.blogger.com/profile/14073963724476846380noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-32116649295311161372014-02-07T16:16:23.856+00:002014-02-07T16:16:23.856+00:00Declination is the angle between true north and ma...Declination is the angle between true north and magnetic north. Grid magnetic angle is the angle between grid north and magnetic north. In the UK we are not expecting to see easterly declination till about 2018. However, because of the relatively large convergence angles in the UK (the angle between true north and grid north), the arrival of easterly grid magnetic angle precedes that of easterly declination. It starts in 2014 in the SW and will take about 20 years for the whole country to be affected. Easterly grid magnetic angle is likely to be around in the UK for more than a century, but it's hard to say exactly how long.BGS Geomagnetismhttps://www.blogger.com/profile/00582120463256218907noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-40669576775345463822014-02-06T17:14:28.402+00:002014-02-06T17:14:28.402+00:00When the time arrives to have Easterly Declination...When the time arrives to have Easterly Declination, another mnemonic could be:<br />Map to Field = Get Rid<br />Field to Map = should Add<br /><br />when are we expecting these changes? (mid 2014 means?) are they gonna cover the whole UK? when these changes are here, are they gonna stay for 350 years?<br /><br />thank you for your timeAnonymoushttps://www.blogger.com/profile/14073963724476846380noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-19636047922704004872014-02-03T13:02:58.172+00:002014-02-03T13:02:58.172+00:00Thanks for your comments. CADET is a popular one b...Thanks for your comments. CADET is a popular one but is strictly speaking only applicable for maps and charts where the north lines are true north lines and not grid north lines. And as one is normally going from "True" to "Compass", you have to remember to apply it in reverse, i.e. subtract easterly magnetic variation/declination. Perhaps additional information that is easy to forget in the heat of the moment. The lack of specificity of the type of north in "East is least, west is best" means that it is applicable for both types of maps.<br /><br />I very much hope the Mountain Rescue Teams will not be busy on this account. Grid magnetic angle is quite small as we go through this transition.<br /><br />SusanBGS Geomagnetismhttps://www.blogger.com/profile/00582120463256218907noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-3141947554363948492014-02-01T23:01:54.980+00:002014-02-01T23:01:54.980+00:00MR Lings is spot on. "Compass to True, Add E...MR Lings is spot on. "Compass to True, Add East" - from my GCE O Level Navigation syllabus in 1974. Will OS and the Hydrographic Office be running a major set of reprints of maps and charts as a precaution ? What about a special NOTAM and NOTMAR to highlight the event ?dyvroethhttps://www.blogger.com/profile/01762209402478368727noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-61608856681607709352014-02-01T14:37:15.645+00:002014-02-01T14:37:15.645+00:00Fascinating. I bet the Mountain Rescue Teams will ...Fascinating. I bet the Mountain Rescue Teams will be busy for a while, until the old die-hard map and compass people adjust.Ronhttps://www.blogger.com/profile/02175808088212630854noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-7894266276983004392014-02-01T02:34:12.477+00:002014-02-01T02:34:12.477+00:00Mmmmm. Not sure how I got to this page - other tha...Mmmmm. Not sure how I got to this page - other than Google which normally gets me to where I want to go. It failed in this instance, so maybe it is not aware of your findings and observations!!! (But I rather enjoyed getting lost this once!,,) :-)Gardendatahttps://www.blogger.com/profile/15127678404849257358noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-80172620120738531522014-01-31T19:51:12.678+00:002014-01-31T19:51:12.678+00:00How will this affect my Feng Shui? Will I need to ...How will this affect my Feng Shui? Will I need to reposition my bed?Trollockillsrandhttps://www.blogger.com/profile/09482310433840393382noreply@blogger.comtag:blogger.com,1999:blog-4228590560998272503.post-12814425330916731392014-01-31T18:56:39.443+00:002014-01-31T18:56:39.443+00:00When I was a navy cadet I was taught CADET, Compas...When I was a navy cadet I was taught CADET, Compass>>>True ADd East. We had to take in to account the magnetic declination, and the deviation due to the ships magnetism which varied with direction.Alastair Lingshttps://www.blogger.com/profile/11028857554065131515noreply@blogger.com