At any point on the earth, there is one great circle that is tangent to your latitude circle. That means that at that infinitesimally small point, both circles point in the same direction, i.e due east, but only at that point.
Also note that the plane that cuts the earth at any latitude is perpendicular to the north-south axis of the sphere but is not perpendicular to the surface. The plane that cuts a great circle is perpendicular to the surface. So if you walk along a latitude circle, you are not standing in the plane of the circle but are tilted by the angle of your latitude. > I am having an off list discussion with Dave but I have a photo that you > may find informative. > > I resized them for the list so I hope you can see the latitude lines. > > what you are seeing is my globe oriented on north south axis and correct > angle for latitude. > > I have a ruler close to my location with the zero on a latitude line > > I am pointing the ruler due east, where the sun will rise on the equinox > as it peaks over my horizon. > > As we look straight down you see a deviation from the latitude line of > about 1" at 4" on the ruler. > > Just rough scale 4" = 4,000 miles so 1" equals 1,000 miles = 25% > deviation. > > My horizon is about 50 miles from here so when I look at the sunrise on > the equinox my latitude is > actually about 12.5 miles north of that point on the horizon. > > So it's not an insignificant difference. > > brent > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
