Sailor Mouth Saturday: Parallel

Navigation is key not only to the course and ultimate destination of a ship, but to its safety and the safety of its people as well. Whether by dead reckoning or GPS, good navigation gets the job done. Bad navigation can lead to the worst kind of tragedy. For the most part, today's word is all about finding safe harbor at the end of a cruise.

The word in modern form comes from Ancient Greek where parallassein meant to vary according to Webster's. Para meant beyond and allassein meant to change. You have to admit it is a curious mix but, at this stage in the etymology game, all we can do is go with it.

Essentially, whether at sea or on land, parallel is a word for lines that go out and continue at an equal distance from one another. For the purpose of navigation, parallels are imaginary lines that circle the globe in equidistant patterns marching north and south from the equator. There are ninety such lines in each hemisphere. In this sense, parallel was sometimes used in place of or interchangeably with latitude. "We shall proceed on a course parallel of the Azores."

Similarly, but not quite the same, the term parallel of latitude was used to indicate a circle parallel to the equator passing through a specific, known place such as a city or island. Admiral Smyth tells us in The Sailor's Word Book that the Arabic word for this is almucantar, which has a nice ring to it, I think.

A parallelogram is, of course, a kind of quadrilateral figure whose opposites sides are equal and parallel to one another. A parallelopiped - say that three times fast - is a prism made up of six parallelograms. Made of sometimes clear, sometimes colored glass, these were often set in the top decks of large ships to allow refracted light to shine down to lower decks. A lovely replica of this kind of clever prism is available at National Geographic online.

Parallel sailing is navigation which takes a ship as nearly along a parallel as possible. Parallels of declination are secondary circles parallel to the celestial, not the global, equator. These are used in astronomy as well as navigation.

This last definition of the word naturally leads us to a discussion of another navigational term: parallax. I'll leave it to Admiral Smyth to explain:

An apparent change in the position of an object, arising from a change of the observer's station, and which diminishes with the altitude of an object in the vertical circle. Its effect is greatest in the horizon, where it is termed the horizontal parallax, and vanished entirely in the zenith.

It is easy to imagine that aboard a ship in movement, parallax would come into play often. This in particular when navigating by heavenly bodies such as planets, the sun or the moon. As the good Admiral notes in his entry on this word, the stars are at such a distance from the earth that there is no appreciable parallax either with the naked eye or the instruments available before the 20th century. Annual and diurnal parallaxes relating to the observation of a star from various points on our globe are now more easily discerned with modern technology. To a large degree, however, these are once again issues for astronomers, not navigators.

And so enough of parallels and parallaxes for one day. Were you midshipmen or ship's boys, I'd send you below to write a letter to your mothers. But the Brethren are seasoned sailors, and so I'll raise a mug of grog with ye, mates, and bid you a fair Saturday one and all.

Header: A well crafted, piratical weather vane from the Great Lakes region via the Under the Black Flag team (see sidebar)