A real navigation brain teaser!!

[SnaxMuppet]

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The nautical mile wasn't conceived until AFTER the realisation that the earth was a sphere with meridians. I believe that this discovery was attributed to Pythagoras

So you and matnoo have events the wrong way round

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I don't think that this is quite true... did you read the article that I posted the link to?

If that article is correct then there it shows that the distance was defined back as far as the ancient egyptians... OK, it might not have been called a "nautical mile" but it was a defined measurement of distance even then so it seems.

 

[tome]

The article you posted suggests exactly the same thing: that the 'royal mile' was derived from astrological observations based on an understanding of the zodiac and presumably the spherical nature of the planet earth

How anyone can interpret this the other way round is beyond me!

 

[barnaclephill]

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because who ever counts Australians anyway?)

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Watch it! Some of us Ozzies are reading this.

 

[Dyflin]

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Wikipedia ... along a Meridien ?? No not as I was taught in Plymouth Nautical College for MN .... the arc is related to a circle of latitude a number of degrees displaced from the equator ... I just can't remember the darn latitude number !!!!

I will try and drag out some of my old cadet stuff I kept for Grandchildren !!

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AFAIK, it's a minute of arc at lat 45deg (i.e. middle for diddle, as the earth is an oblique spheroid)

 

[philfin]

A nautical mile is the arc of the earths circmmference subtended by an angle of of one minute at the center of curvature. It varies slightly because the earth is slightly flattened at the poles. it measures 1860m at the poles and 1841 at the equater. A mean length of 1852 is adopted in Navigation.

How the figured it out is beyond me but thats what it is. All to do with an angle of 1 minuit from the centre of curvature, nothing else.

 

[alienzdive]

The minute of arc as above is a minute of angle from the centre of the earth.

I guess that some clever guy some time ago extended the measurement to the stars. They would not have needed to know how far the stars are away but just the angle of the same star from any two points.

 

[Oldhand]

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Carry on measuring as you are except measure 1 minute and not a degree /forums/images/graemlins/smile.gif

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So you noticed my"deliberate" mistake, thanks for correcting it! Oh dear, what old age does to one...

 

[Oldhand]

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However, and this is the key to understanding what I was explaining, 1 deg of latitude will always be 60NM (or very close to it given the irregular shape of the earth) no matter where on the earth you are but that cannot be said about 1 deg of longitude because that distance then also depends on the latitude.

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Strange, you seem to have reversed the definition of a nautical mile as I always understood it, surely it 60nm will always be 1 degree of latitude and not the other way round? I beleive Lat and Lon came first and the nautical mile followed, mais non?

I don't know what all the fuss is about, as long as it is understood the earth is an oblate spheroid, the definition of a nautical mile as a minute of latitude at the latitude you are at is very simple to understand.

 

[SnaxMuppet]

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Strange, you seem to have reversed the definition of a nautical mile as I always understood it, surely it 60nm will always be 1 degree of latitude and not the other way round?

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Sorry, I do not see what you are saying here... surely if:

1 deg = 60NM
then
60NM = 1 deg

You seem to be disagreeing with me but it isn't clear what you disagree with because you agree with me in your text!!! /forums/images/graemlins/confused.gif