New Scientist magazine has a feature called "The last word", in which readers' questions are answered by other readers.

Recently one reader's question asked what point on earth was farthest from the nearest sea, meaning farthest from any inlet of the world ocean. Rivers don't count, just seas, connected to the world ocean and subject to tides of the whole sea, not just seiches.

A reply was published, calling this point the "continental pole of inaccessibility (CPI)", that said the question was raised in the 1960's when builders of submarine-mounted nuclear missiles wanted to tout an ability to target any point on land from a body of water accessible to the sub fleet.

The reply stated that the point is at 46°17'N, 86°40'E, in northwest China near the Russian border, and went on to say that the nearest arm of the sea was 2848 km away at Tianjin on the Yellow Sea. It stated further, that the sub proponents neglected to mention in promotional literature that as the rockets had barely enough range to cover this distance, that "to strike the pole [of inaccessibility] a large nuclear-powered submarine would practically have to visit Tianjin docks."

What's wrong with that reply to the reader's question?

I admit I do not follow Brianjn's and Charlie's remarks.

One possibility is that Charlie is challenging us to clarify whether there may be a more ociean remote location than Xinjiang. However, even after repeated readings of the problem, it is hard for me to find support for this interpretation.

Another thought that comes to mind (triggered, improbably, by an inclusive interpretation of Charlie's suggestion to think topologically) would be to criticise the notion of point to point distance on a sphere: The distance quoted in my earlier comment was the distance along a great circle connecting Chorowika with the CPI (i.e., a portion of the earth's circumference). An alternative notion would be to take a straight line measurement beneath the earth's surface. This would change the distances, but leaves question of which nautical point closer to the CPI unchanged.

Finally, one last thought: throughout the duration of the missiles trajectory the earth will be rotating. For the purpose of missile targetting, we would have to consider the differential rotational speeds of the launch point and the target. This is especially relevant for the Chorowika site, as the large difference in latitude makes for a more differential than would be the case with Tianjin.

Posted by FrankM on 2008-05-15 07:23:07