🔍 Key Concepts

• Parallel sailing: using departure and difference of longitude to find distance on the same latitude • Difference of longitude (DLo) between two meridians and converting degrees to minutes of arc • Using cosine of the latitude to relate DLo to distance along the parallel

💭 Think About

• First, compute the numerical difference in longitude between 14°00'W and 03°20'W. Is the longitude increasing or decreasing as you move east? • Convert that difference in longitude from degrees and minutes to total minutes of arc, then think about how many nautical miles that would be at the equator. • Remember that on a parallel of latitude, the actual distance is less than at the equator. How does multiplying by the cosine of the latitude change your answer?

✅ Before You Answer

• Be sure you have the correct DLo (in degrees and minutes) before you convert to minutes of arc. • Use the given latitude (59°12'N) in your cosine term; don’t use the equator or any other latitude. • Check that your final distance is reasonable: it should be less than the distance you’d get if you assumed 1° of longitude = 60 NM without the cosine.