🔍 Key Concepts

• Great-circle sailing vs. Mercator sailing and when each gives the minimum distance • How a gnomonic chart represents great circles (as straight lines) and how to transfer that to a Mercator chart or plotting sheet • The effect of a latitude restriction (51° N limit) on a great-circle track and when you must use parallel sailing

💭 Think About

• On the gnomonic chart, what happens to the great-circle track between the two positions—does it ever go north of 51° N? If so, between roughly which longitudes? • If a great-circle would exceed 51° N, what is the shortest way to modify the route: change the whole track to Mercator, or only replace the part that violates the limit with a segment along a parallel? • Look carefully at options that mention 51° N: which ones keep the great-circle portions where they are shortest, and only ‘flatten’ the part that would otherwise exceed the latitude limit?

✅ Before You Answer

• Verify on the gnomonic chart whether the unrestricted great-circle crosses 51° N and identify the entry/exit longitudes where it touches/crosses that parallel. • Check which options use great-circle segments where allowed (south of 51° N) and parallel sailing along 51° N only where necessary, instead of using Mercator for large portions of the route. • Confirm that the proposed intermediate positions (lat/long given in the answers) actually lie on or very near the plotted great-circle and/or the 51° N parallel as stated.