We’re starting a brand-new chapter now: Earth Magnetism — Page 49, Lesson 50

We’re starting a brand-new chapter now: Earth Magnetism. This is one of the most practical chapters in your General Navigation syllabus, because it explains why your compass doesn’t always point where you think it should, and how we correct for that. Let me give you the roadmap of what this chapter covers, because the structure itself tells you a lot about how the subject hangs together. We begin with True Direction, then Magnetic Direction, then Magnetic North. Those three are the foundation — they define the reference lines we measure everything against. After that we get into Variation, which is the angular difference between true north and magnetic north. Then we look at how variation changes depending on where the observer is on the Earth, and there’s a special section on the situation at the poles, because things behave very differently up there. Then we move to the Real Variation Map — that’s the actual chart of variation across the globe, not the simplified model. We look at real variation at the poles, then how variation changes over time, and how we update isogonals — those are the lines on a map joining points of equal variation. After that comes Magnetic Dip Angle, which is a completely different effect, then Deviation, which is the error caused by the aircraft’s own magnetic fields. Finally we bring it all together in the Application of Variation and Deviation, and the chapter closes with a set of Definitions, then Questions and Answers. So the whole chapter is really a progression: establish the true reference, introduce the magnetic reference, then layer on the two corrections — variation, which is Earth-related, and deviation, which is aircraft-related. Let’s start at the very beginning with True Direction, because everything else is defined relative to it.