I spend an inordinate amount of my spare cycles thinking about latitude and longitude. Today I went looking for some ballpark figure to use that would let me approximate measurement in degrees, minutes and seconds of latitude in miles. I was intrigued to find that:

The nautical mile was historically defined as a minute of arc along a great circle of the Earth.

An extremely helpful forum post tells more of the story.

Special bonus revelation: speed measured in *knots* is really just speed measured in *nautical miles per hour*.

Stay tuned for picas, points and agate lines.

## Comments

“Extremely helpful post” indeed….it really gets down to the Long and Lat of it.

nautical mile: A nautical mile is a unit of distance that is used on the water; it is equal to 1.15 miles or one minute (1/60 of a degree) of longitude.

One thing to remember. Since the earth is a spehere, the distance between lines of lingitude will decrease to zero at the north and south poles. Because of this, I think, the actual distance is measured at 45 degrees latitude (half way between the pole and the equator).

Time is in the mix too, because Earth turns 15 degrees longitude per hour (24 hours/day X 15 degrees/hour = 360 degrees/day). I think 2000 regular miles is 15 degrees at the equator, so Earth is 24,000 miles around the equator. If I recall rightly. Anyway, point is, this is the one way metric sucks by comparison. The explanations for metric units are so boring and unmystical.

Everybody read Dava Sobel’s book

Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time? Was a best seller I think. I highly recommend it.