🔍 Key Concepts

• Great circle sailing formulas for distance and initial course on a sphere • Converting longitudes correctly when one is East and the other is West to get difference of longitude (DLo) • Using the relationship between latitude, difference of longitude, and initial course at departure

💭 Think About

• First, compute the total difference in longitude between 140°20.5’E and 122°51.0’W and be careful about the 180° meridian. Is the shortest path across the Pacific or via Europe? • Think about what kind of initial course (northeasterly, northwesterly, etc.) you would expect when going from 35°N, 140°E to 47°N, 123°W on a great circle. • Use the great circle distance formula to get a central angle in degrees, then convert that angle to nautical miles. Which option is closest to that result?

✅ Before You Answer

• Verify the difference of longitude (DLo), remembering that East to West is found by adding longitudes and comparing to 180°. • Confirm that you’re using nautical miles = degrees × 60 after finding the great circle central angle in degrees (or converting from radians properly). • Check whether the initial course should be in the 030–050°T range or about 070–080°T based on the geometry of the route on a globe.