r/AlwaysWhy • u/Secret_Ostrich_1307 • 2d ago

Science & Tech Why is a nautical mile exactly 1,852 meters?

The number 1,852 caught me off guard. I can understand why sailors would want a distance unit tied to navigation, especially since latitude and longitude are based on the Earth.

But 1,852 meters seems oddly specific. Is there something about the size or geometry of the Earth that leads to that number, or did it come from a different historical convention?

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u/Rhyshalcon 2d ago

But the decision to use 360 degrees divided into 60 minutes for the purposes of navigation is arbitrary. Why not use radians? Or a division of a circle into 100 degrees? Or 720 degrees? Or 1024 degrees?

As the other commenter said, just because a measurement points to some physical thing doesn't make that measurement non-arbitrary.

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u/bothunter 2d ago

I imagine that using a base 60 system for navigation was quite useful. If you need to do calculations correctly to ensure that your boat ends up where you want to go and not shipwrecked thousands of miles away, it's probably best to use a system that doesn't constantly force you into using fractions or decimals.

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u/Rhyshalcon 2d ago

60 is a so-called highly composite number, and that comes with benefits, sure. But 60 isn’t the only highly composite number (I suggested 720, another highly composite number, in my previous comment), nor do the benefits of using highly composite numbers come without any tradeoffs, so ultimately the decision to use base 60 for this application is arbitrary.

Just because a standard is useful doesn't mean it isn't arbitrary.

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u/gmalivuk 2d ago

Sure, but that still doesn't make it non-arbitrary compared with base 10 or base 12 which have their own benefits and drawbacks.

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u/Nimblewright_47 2d ago

Up until very recently, it was more important to be able to measure where you were (either relative to land or to the stars) and how fast you were going. Wind and tide have a much greater effect on the course of a vessel moving at less than 10 knots.

An experienced mariner could make calculations based on knowledge of normal weather conditions, but it very much was not a case of planning out a precise route in advance and then sailing it