🔍 Key Concepts
• Mercator sailing relationships between difference of longitude, difference of latitude, meridional parts, and course
• How to determine the quadrant of the course from the starting and ending latitudes and longitudes
• Using the mid-latitude or meridional parts to estimate distance and check if the result is reasonable for an Atlantic crossing
💭 Think About
• From 49°45' N, 6°35' W to 25°50' N, 77°00' W, is your longitude increasing east or west, and is your latitude increasing or decreasing? What general direction (NE, SE, SW, NW) does that imply?
• In Mercator sailing, how do you use the difference in meridional parts (dMP) and difference of longitude (DLo) to find the course? Which trigonometric function relates them?
• Once you compute the course, how do you use the difference of latitude (DLat) and the course to find the distance, and does that distance seem reasonable for the region of the North Atlantic involved?
✅ Before You Answer
• Confirm the correct signs for DLat and DLo (north/south, east/west) and therefore the correct course quadrant
• Make sure you use meridional parts for both latitudes and take their difference before using the trig function
• After computing distance, check whether a back-of-the-envelope great-circle estimate gives a similar order of magnitude (around a few thousand miles), so you can eliminate clearly unreasonable options