🔍 Key Concepts

• Great-circle sailing vs. rhumb-line (Mercator) sailing • Using the spherical trigonometry formula for initial course: involving difference in longitude and the pole-to-position triangles • Interpreting the quadrant of the initial course from relative positions (N/S and E/W) of departure and arrival

💭 Think About

• Look at the starting and ending latitudes: are you generally moving more northward or southward as you proceed from the departure to the destination? How does that affect whether the initial course must be in the NE, NW, SE, or SW quadrant? • Compare longitudes: you begin in the western hemisphere and end in the eastern hemisphere. Thinking in terms of great circle, what general direction (eastward or westward) must you steer initially? • When you compute or estimate the initial great-circle course, is it closer to a meridional (N–S) direction or zonal (E–W) direction, and which answer choices are consistent with that?

✅ Before You Answer

• Confirm which hemisphere (N/S and E/W) each position is in so you can determine the general direction of travel • Make sure your approximate initial course direction makes sense for a great-circle track (which may start by going somewhat poleward before curving toward the destination) • Eliminate any options whose quadrants (e.g. NE, NW, SE, SW) are inconsistent with the overall change in latitude and longitude between the two points