🔍 Key Concepts

• Parallel sailing keeps the same latitude; only longitude changes • Difference of longitude (DLo) must be converted to minutes of arc along that parallel using the cosine of the latitude • 1 minute of arc of longitude at a given latitude = cos(latitude) nautical miles

💭 Think About

• First, determine whether you are going east or west in longitude between the two positions, and think about what that means for the true course (090°T vs 270°T) • Compute the total difference of longitude in degrees and minutes between 152°49'E and 176°12'E, staying on the same side of the 180° meridian; then think about how to turn that DLo into distance at 49°38'N • Ask yourself: if you sailed due east or due west along a parallel at higher latitude, is one degree of longitude more than, less than, or equal to 60 NM?

✅ Before You Answer

• Be sure you calculate the difference of longitude correctly in degrees and minutes • Use the correct formula: ( \text{Distance (NM)} = \text{DLo (minutes)} \times \cos(\text{Lat}) ) • Confirm that your final distance is reasonable for crossing that many degrees of longitude at about 50°N (not as large as at the equator, where it would be 60 NM per degree)