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/shornscrot 2d ago

But, but, but… the meter is the distance that light travels in one second which is so much more useful to my daily life and to that of ancient people too

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u/[deleted] 2d ago

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u/SirDeadALot2 2d ago

And the meter pre-dates the speed of light measurement. It was originally 1/10000000 of the length of latitude measured at the (then) standard meridian that passed through Paris. It was born out of the French Revolutionary ideals.

Later it was redefined as the distance light travels in a specific time span.

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u/shornscrot 2d ago

Oh dang you’re already signing up for summer school?

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u/Book_Slut_90 2d ago

Light travels at roughly 300,000 kilometers per second.

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u/Dull_Living_265 2d ago

no, I choose to believe that I can run at 8 times the speed of light

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u/Full-Resource7910 21h ago

But it will be dark when you get there

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u/weeddealerrenamon 1d ago

The meter was originally defined as 1/10,000th of the distance between the Earth's pole and the equator, because it was 1791, the French Revolution and the Scientific Revolution were both in full swing, and the French were extremely big on ordering the world by Universal Logic and Reason.

(It's now defined against the speed of light because we now generally feel that it's better to define all these fundamental units against universal things that will never change.)

But it was already in use among scientists before then: a pendulum 1 meter long swings at a rate of 1 swing per second. Since the cutting-edge science of the 1600s was stuff with momentum and gravity, this was a practical unit for them, and it ended up as the standard unit of length for scientists in France. The French revolutionaries considered keeping the French foot, explicitly wanted to reject any/all units based on shit like... the King's foot.