In the navy, you’re not a true sailor until you’ve crossed the equator. So whenever a ship makes the crossing, it holds a ceremony in which a sailor representing “King Neptune” challenges “pollywogs” for invading his domain, and there follow two days of general hazing from which the newbies emerge “shellbacks.”

In the centuries since this started, there has emerged a kind of graduate school of advanced crossings. Cross the equator at the international date line and you become a golden shellback; cross it at the prime meridian, near West Africa, and you’re an emerald shellback.

This becomes an exercise in spherical geometry. Presumably a member of the Order of Magellan (a sailor who has circled the globe) automatically joins the Order of the Golden Dragon (for crossing the international date line) unless he’s also joined the Orders of the Blue Nose and the Red Nose (for crossing the Arctic and Antarctic Circles). There must be a chart somewhere.