🔍 Key Concepts

• Use the great circle formula on a sphere: relate the two latitudes and the difference of longitude (DLo) to find the central angle (angular distance). • Convert all angles (latitudes and longitudes) to degrees and minutes, and be consistent with east/west longitudes when finding DLo. • Use the formula for initial great circle course at the point of departure, which involves the difference of longitude and the two latitudes (often using spherical trigonometry or Napier’s rules).

💭 Think About

• What is the correct difference of longitude between 18° 23.1' E and 73° 49.4' W, and should you add or subtract them? • After finding the central angle (in degrees) between the two positions, how do you convert that angular distance into nautical miles? • Given your computed initial course (true), which option matches both your distance and course quadrant (NW, NE, etc.) from the starting point in the South Atlantic near South Africa to the U.S. East Coast?

✅ Before You Answer

• Make sure you have the correct DLo (remember E to W often means adding the magnitudes). • Check that your distance in nautical miles is approximately the central angle (in degrees) × 60; if it’s very different, recheck your math. • Verify the initial course’s general direction: from 33° S, 18° E to 40° N, 73° W, should the track start heading generally northwest, southwest, northeast, or southeast? Eliminate answers whose course doesn’t fit this.