SUBCOURSE EDITION - Modern Prepper

Figure 4-1. Determination of latitude and longitude.b. A great circle is an imaginary circle on the earth's surface, the plane of which passes throughthe earth's center. Each meridian is one half a great circle in length, (two opposite meridians make onegreat circle) and all meridians converge at the two polar points. Longitude is reckoned from 0° to 180°east and west from Greenwich, the Zero Meridian.c. Latitudinal measurements are expressed in terms of parallels, each of which is a line whichencircles the earth at a constant distance north or south of the equator. No parallel of latitude, exceptthe Equator, is a great circle; that is, their planes do not intersect the earth's center but cut through theearth parallel to the plane of the Equator. Parallels are numbered from 0° at the Equator north andsouth to 90° at the poles.126