Diane Dyer, age 10, of Omaha, Nebraska, for her question:

Are knots the same as miles?

Both knots and miles are measures of distance. But knots are tied to the clock, just as miles are related to time on a speedometer. On land the speed of a car is rated in miles per hour. At sea and in the air, pilots estimate their rate of speed in knots, which are also miles per hour. However the so called statute mile used to measure distances on land is about 796 feet shorter than the mile used to estimate knots in the air and on the sea. The land mile, after many changes through its long history, is now taken to be 5,280 feet.

Pilots and seamen use a mile based on the size of the earth. Imagine a complete circle around the globe. Divide it into 360 equal degrees and then divide a degree into 60 equal second units. This is how experts figure the value of the geographical mile, alias the nautical mile. We take it to be 6,076 feet. A ship traveling at one knot goes one nautical mile per hour; at ten miles per hour its speed is ten knots. True sailors give the speed of a ship in knots    and never, never say knots per hour.