# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: What is a degree of latitude?**

**From:**Nicol�s de Hilster

**Date:**2008 Mar 23, 21:08 +0100

A degree of latitude of course depends on how you define the surface you calculate it on. Suppose you want to know it for the WGS'84 ellipsoid the following applies: semi major axis (a) = 6378137.000 inverse flattening (Finv) = 298.257223563 the formulas you need for the calculation: e2=(1/Finv)*2-(1/Finv)^2 mu = a/SQRT(1-e2*SIN(phi)^2) rho = a*(1-e2)/SQRT((1-e2*SIN(phi)^2)^3) 1" lat = rho*SIN(1/3600) 1" lon = COS(phi)*mu*SIN(1/3600) If we fill those in for 53 degrees north, the semi major axis and inverse flattening we get: e2 = 0.00669437999 mu = 6391797.44772 rho = 6376233.57268 1" lat = 30.913m 1" lon = 18.649m If you need 1 minute you simply multiply with 60, for one degree multiply with 3600. Nicol�s Lu Abel wrote: > This seems quite silly, but I realize that I don't know the "official" > definition of a degree of latitude. > > I'm sure most on this list know that the earth is an oblate spheroid -- > it's fatter than it is tall. This means if I cut the earth in half > through its poles, the resulting cross-section looks like an ellipse, > wider than it is tall, rather than a perfect circle. And this > elliptical cross-section can lead to two possible definitions of a > degree of latitude. > > If take a cross-section of the earth and draw an angle one degree up > from the equator, is the place where this line intersects the surface of > the earth the first (degree) parallel? Or is the first parallel one > ninetieth of the way from the equator to the pole? > > Years ago I took an offshore navigation course that taught the various > "sailings," including use of the Meridional Parts table from Bowditch to > determine a rhumb line course when traversing long distances (especially > those with dramatic north-south differences). (Meridional Parts give > the "stretch" in the latitude scale required at various latitudes to > create a Mercator chart). As I recollect, the meridional parts down > near the equator are actually slightly less than 1.00000, which would > indicate that the first of my two definitions is the correct one. > > I know there are some experts in cartography on the list, I'm sure this > is trivial for them. > > Lu Abel > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavList-unsubscribe@fer3.com -~----------~----~----~----~------~----~------~--~---