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At the Equator, the circumference of the Earth is about 25,000 miles; so one degree of longitude is about 25000 / 360 = 69.4 miles, and one minute is 69.4/60 = 1.15 miles. Originally, a ''nautical mile'' was intended to be one minute of longitude at the equator. (The nautical mile is now ''defined'' to be exactly 1852 meters, so a minute of longitude is actually 1.0018 nautical miles). A second of longitude is only about a hundred feet; before GPS, it was difficult to measure longitude to an accuracy of a second.
At the Equator, the circumference of the Earth is about 25,000 miles; so one degree of longitude is about 25000 / 360 = 69.4 miles, and one minute is 69.4/60 = 1.15 miles. Originally, a ''nautical mile'' was intended to be one minute of longitude at the equator. (The nautical mile is now ''defined'' to be exactly 1852 meters, so a minute of longitude is actually 1.0018 nautical miles). A second of longitude is only about a hundred feet; before GPS, it was difficult to measure longitude to an accuracy of a second.
In 1995, a book entitled simply ''Longitude,'' by Dava Sobel, made the nonfiction bestseller list. It tells the story of John Harrison's development, in the 1700s, of the first marine chronometer accurate enough to determine longitude at sea.
Although lines of longitude may be imaginary, they are very important to navigators; [[Lewis Carroll]] joked about this in his long nonsense poem [[The Hunting of the Snark]]:
Although lines of longitude may be imaginary, they are very important to navigators; [[Lewis Carroll]] joked about this in his long nonsense poem [[The Hunting of the Snark]]: