Re: Wobbly Prime Meridian
From: Peter Fogg
Date: 2010 Nov 23, 13:39 +1100
My understanding, which may be subject to correction, is that 1,852 metres was adopted by international consensus as being a good average suitable for navigational purposes over moderate extents of latitude - which is where most navigation happens.
Have a look at what Wiki has to say on the subject, including:
"The international nautical mile was defined by the First International Extraordinary Hydrographic Conference, Monaco (1929) as exactly 1852 metres. ... It varies from approximately 1842.9 m at the Equator to approximately 1861.7 m at the Poles, with a mean value of 1852.3 m. The international nautical mile was chosen as the integer number of metres closest to the mean sea mile.
Gary LaPook wrote:
One minute of longitude is 1852 meters at the equator but progressively smaller as you approach the poles, it varies with the cosine of the latitude. The cosine of 51� 28.674' is .6228 so the error is 1852 meters times .088 times .6228 which comes to 101.50 meters.