🔍 Key Concepts

• Great circle vs rhumb line behavior on a Mercator projection in mid-North Atlantic latitudes • How to locate and think about the vertex of a great circle in the Northern Hemisphere • Correct method for measuring great-circle distance using a gnomonic plotting chart and a Mercator chart

💭 Think About

• On a Mercator chart in the North Atlantic, if you draw the great-circle between Iceland and the Azores, which side of that curve would the British Isles be on? Visualize or roughly sketch it. • For a great-circle between two northern latitudes, will the Northern Hemisphere vertex usually be north or south of the higher-latitude departure point? Think about how aircraft tracks behave on long-haul polar routes. • Compare the great-circle distance to a rhumb line for a several-hundred-mile passage at these latitudes: is the difference normally significant or negligible?

✅ Before You Answer

• Verify which way a great-circle track curves relative to mid-Atlantic landmasses (Greenland, Iceland, British Isles, Azores) on a Mercator chart. • Confirm the definition of the vertex: the point of maximum latitude on a great circle between two points in the Northern Hemisphere. • Review the standard procedure for measuring great-circle distance from a gnomonic chart: how do you transfer and measure it on a Mercator chart—by short segments at what reference latitude?