Re: [Paddlewise] Latitude distances

Dave Williams asked:

...<snip>...
> 1 degree of latitude equals 60 nautical miles right? And, there are 360
> degrees in a circle right?  How can there be 360 degrees of 60 nautical
> miles each (degree) at both the equator and at latitude 60?  The circle, of
> course, is much much smaller at the 60 degree latitude.
> 
> What's going on here?

Well, what's going on is that Dave is either confused (it happens to all
of us) or is trolling.  :-)  If it's the latter, than I have taken the
bait...

Yes, there are (approximately) 60 nautical miles in a degree of
latitiude.  And yes, the parallel circles become smaller as one moves
away from the equator.  But what this implies is that a degree of
*longitude* (not latitiude) decreases in length as one moves away from
the equator.  

The 360 degrees that you mention along each parallel circle are 360
degrees of *longitude*.  As you travel along a given parallel your
latitude remains constant--it is your longitude that is changing.  Since
the circumference of these parallel circles decreases as you move toward
the poles, it must be the case that length of a degree of longitude
decreases as you move toward the poles.  

On the other hand, the distance *between* two parallel circles (one
degree apart) is the length of a degree of latitude, and this distance
remains (essentially) constant as you move from the equator toward the
poles.  For example, the distance between the parallel at 1 degree of
latitude and the parallel at 2 degrees of latitude is (approximately) 60
nautical miles, and the distance between the 51-degree parallel and the
52-degree parallel is also (approximately) 60 nautical miles.  The
length of a degree of latitude is (approximately) the same, regardless
of the distance from the equator.  

Now for the bonus questions (both of which are irrelevant from the
standpoint of practical navigation).  As I noted above, the length of a
degree of latitude is "approximately" constant.  Why does it vary
ever-so-slightly (that part is easy) and at about what latitude does it
achieve maximum length?   

Dan Hagen
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