A Knot is the speed of Nautical Mile per hour. The name for a Knot is derived from the 17th Century practice of measuring speed using a "chip log", this was a wooden wedge attached to a piece of rope with knots tied every 47'3". The wood was thrown overboard, and over the course of 30 seconds the amount of knots that passed out were counted, thus the ships speed could be calculated. The Nautical mile itself is equivalent to that of 1.15 survey miles (or Land miles), thus a knot is equivalent to 1.15 land miles per hour.
The length of a nautical mile is defined as the angular distance of one minuet of arc on the Earth's surface. That is to say, if you were to break up the equator in to 360 equal sections (or degrees), and then broke each of those up in to a further 60 sections (or minuets), a nautical mile is the distance of one of these minuets. Of course the earth is not completely spherical, so in truth arc minuet distances vary from pole to pole.
The length of a nautical mile is defined as the angular distance of one minuet of arc on the Earth's surface. That is to say, if you were to break up the equator in to 360 equal sections (or degrees), and then broke each of those up in to a further 60 sections (or minuets), a nautical mile is the distance of one of these minuets. Of course the earth is not completely spherical, so in truth arc minuet distances vary from pole to pole.
