Perigee and Apogee: The point of closest approach of the satellite with to the earth' s center of mass is called perigee and the most distant position is the apogee. Nodes: The intersection between the equatorial and the orbital plane with the unit sphere is termed the nodes, where the ascending node defines the northward crossing of the equator. ae E apogee geocenter perigee 電 Principles of the Global Positioning System 2005-3-11(3 Introduction Principles of the Global Positioning System 2005-3-11(42 Principles of the Global Positioning System 2005-3-11 3 Principles of the Global Positioning System 2005-3-11 4 Introduction