# What is a Nautical Mile?

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

Peter on March 24, 2006 - 18:09

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

gm on March 27, 2006 - 01:01

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).

oliver on March 27, 2006 - 04:40

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.

oliver on March 27, 2006 - 04:44

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.