31–40 of 51 posts
> A kilometer is also defined using the planet Earth as a standard of distance. Wrong. It used to be that way, but not anymore.
Which is why it says: ... you would have the traditional unit for the kilometer as defined in 1791 by the French Academy of Sciences.
The article doesn't mention that it's not the current definition.
At what elevation are they measuring these arcs / circumference of the earth? At sea level? Feel like that needs to be explicit if we are trying to be technical. Because you can't "travel around the Earth at the equator" in "21,600 nautical miles, 24,857 miles or 40,003 kilometers" without going underneath a mountain or two.
It’s a surface describing constant (magnitude of) the acceleration of gravity.
At what elevation are they measuring these arcs / circumference of the earth? At sea level? Feel like that needs to be explicit if we are trying to be technical. Because you can't "travel around the Earth at the equator" in "21,600 nautical miles, 24,857 miles or 40,003 kilometers" without going underneath a mountain or two.
P.S.: Supply Corps, so never needed to know it.
It's the only mile that metric people approve of :-)
No, the nautical mile is hated by proponents of the metric system. As with all customary units, it favors a specific use-case at the cost of errors and conversions, has limited accuracy and doesn't handle orders of magnitude.
As I'm typing this, I'm looking at the power extension cord for my computer, which has a thickness 1.10 Micro Nautical Mile, ie. AWG 12, ie. 2.05mm…
Earlier quoted context omitted.
I can believe that it's true that lines of longitude are not great circles, but I can't picture why in my head. Isn't a great circle formed by extending the shortest distance between two points on the surface of a sphere?
An arc along a line of longitude is a deviation in the latitude scale. Lines of longitude lie on great circles since they converge on the poles, but when you move a degree of longitude you are moving west or east along a line of latitude, and the only line of latitude which is a great circle is the equator. The reason you use the latitude scale is that lines of latitude are equidistant between one another - it is the…
I don't believe that is correct. The latitude scale of a Mercator projection chart will not be constant because the projection introduces some distortion. So 1NM at the top of the chart will not be the same distance as 1NM at the bottom of the chart. For this reason, you should always place your dividers roughly in the area you are going to be sailing in.
As I recall from my Yachtmaster course, the difference is not usually that great for day to day stuff, but for planning long passages on small scale charts it could be a significant error.
Its interesting that the nautical mile is based on a more abstract number that would define when looking at maps and charts, rather then something more immediate and physical like the distance to the horizon when out on the ocean. Most imperial units seem to be based on simple laymen measurements.
This makes measuring distance in nautical miles using a chart a lot more practical.
Its interesting that the nautical mile is based on a more abstract number that would define when looking at maps and charts, rather then something more immediate and physical like the distance to the horizon when out on the ocean. Most imperial units seem to be based on simple laymen measurements.
Distance to the horizon is variable. Sea state, height of deck over water, visibility etc will all affect it. Whereas, with a sextant and a decent maritime chronometer it is very easy (*) to determine longitude and latitude.
> A minute of arc on the planet Earth is 1 nautical mile. Only if that minute of arc lies on a great circle route. As an interesting addendum, when measuring distance made good on a nautical chart, you will use a divider to measure the straight line distance, then lay this onto the latitude scale to convert it to nautical miles. If you were to use the longitude scale, you would be off by approximately the cosine of y…
I'm pretty sure to derive a nautical mile you have to use the equator, not just any great circle, because the earth isn't a sphere.