6 ms·

Did I miss something, why 14.4m between knots? Or why set 1.852 kilometers as the nautical mile?

• jmj42 12y ago
  From Wikipedia: "The nautical mile is a unit of length that is approximately one minute of arc measured along any meridian."
  • deelowe 12y ago
    Still doesn't answer "why." More specifically, why is it more advantageous to measure it this way versus some other way? Why do airplanes measure their speed/distance in knots? Why not cars, trucks, runners, and physicists?
    • jtarrio 12y ago
      It's just a convenient way to define a unit of length. Look up the original definition of the metre and you'll see that it's basically the same except for some constants.
      • Tloewald 12y ago
        The metre was originally defined as 1/10,000 of the distance from the equator to the north pole through Paris. There's a corresponding measure of angle (gradian -- 1/400 of a circle) which has never become widely adopted (although my old casio calculator supported it)
    • andyjohnson0 12y ago
      Ships and airplanes traditionally navigate using latitude/longitude measurements. Since that coordinate system is based on degrees/minutes/seconds of arc, a length unit that uses the same system is more natural.
      • deelowe 12y ago
        ;-) I kind of knew this already, but thanks for confirming. Point being, there's not a good reason "why" today. Truth is that it's convention at this point. People used to use maps and various tools to do navigation by sea and air. The methods they developed assumed certain things (traveling in an arc, usage of maps with lat/long lines, etc..), which meant the knot was more preferable.
        • escherplex 12y ago
          Valid points all but we're using 20/20 hindsight to render judgments on received conventions during a time in which the more logical metric system exists. A quick glance at 'Knot (unit)' in Wikipedia supplies a 'rationalization' for the use of knots involving old Mercator projection navigation maps. But all of these 'knots' and 'mile' measures are based on the English 'foot'; where did the old 'foot' standard come from? Some 10/11 convention imposed by an English King Henry III on an older system. And by extension, why retain 24 hours in a solar day or the Babylonian 360 degrees in a circle? Or more recently, why the Cartesian convention of ordinate-vertical and abscissa-horizontal on graphs rather than the other way around (sundial-clockwise would be positive; back-Kronecker [0 1,1 0] to convert)? After a while these mathematical musings start to resemble idle etymological ramblings in linguistics: eg, 'extreme' conflates 'out of' and 'sewer'; but then why those particular phonemes for the sense of 'out of' or 'sewer'? As my brother the research psychiatrist frequently retorts "You're trying to be logical. People aren't logical"
          • bsder 12y ago
            24 and 360 are really good unit bases for something you have to divide by hand. 24 gets you 2/3/4/6/8/12 while 360 gets you 2/3/4/5/6/8/10/12/15/18/20/24/30/36/45/60/72/90/120/180 And, we don't always adhere to cartesian conventions. Right-hand and left-hand rules abound in engineering. And even computer graphics regularly flips the axis directions depending upon usage (perspective transforms, for example). And, decimal degrees isn't that uncommon either.
        • tomkarlo 12y ago
    • snake_plissken 12y ago
      You don't travel on along a great circle when you driving or running. But when you are flying and sailing long distances, you do.
• jtarrio 12y ago
  The nautical mile is the length of a minute of arc along a great circle on the surface of Earth. I think the 14.4m figure is wrong; that should be 15.4m, which is the distance covered in 30 seconds by a vessel going at 1 nautical mile per hour.
  • maxerickson 12y ago
    I'm randomly reading some of the links here. The Wikipedia article on the Chip log associates the 14.4 meters with a 28 second sandglass.
• gpvos 12y ago
  It was originally 7 fathoms. Later the value was refined a bit because of newer measurements and updated definition of the nautical mile. Why 7, I don't know. Wikipedia seems to indicate that the definition of a knot was derived from that of a nautical mile, but I wonder if it wasn't the other way around originally. https://en.wikipedia.org/wiki/Chip_log#Origins https://en.wikipedia.org/wiki/Chip_log#Origins
• protomyth 12y ago
  Because the article insists on using metric when using other units would have made for a much better explanation since it would show the evolution and not be confusing like 14.4m. rdl and other explain the reason for a nautical mile above: https://news.ycombinator.com/item?id=7559252 https://news.ycombinator.com/item?id=7559252
• logfromblammo 12y ago
  There are approximately 40000 km in a great circle passing through both poles and Paris. 40000 km / 360 degree * 1 degree / 60 arcminute = 1.851... km / polar arcminute if 1 knot is 1 arcminute / hour, then to get the distance in meters per knot, you use the following factors: 1.851... km / hour * 1000 m / 1 km * 1 hour / 60 minutes * 1 minute / 60 seconds * 30 seconds / knot = 15.432 m / knot