The Sexy Sextant

A sextant on display at Oddyssea in Half Moon Bay, California.

Recently we had some visitors who asked “How does a sextant work? They look so cool!”

Well, if you know anything about Mike, this is a tantalizing question that he was prepared to expound upon until our guests begged for mercy (ok, until they decided to leave with a sextant 😉 )

Fundamentally, a sextant (name derived from six as the measurement arc is 1/6th of a circle) is a device used to measure angles. In the years before Global Positioning Systems, it was a favored tool for navigation on the high seas. The device itself is pretty simple, it consists of an eye piece which may or may not have magnification, a reflecting mirror, and a pivoting arm calibrated to an arc measurement scale.

To use a sextant, one sites a horizon, real or artificial, through the view finder and then adjusts the pivot arm so that the object one is interested in is level with the horizon. It’s a split view to facilitate this. Then one looks at where the pivot arm is positioned against the arc measurement to get the angle in degrees. You can use this to measure horizontally, it’s also possible to use vertically for angle measurement.

Fundamentally, that’s how to use the tool. Now, if you’re navigating, you use the angle, the time, and a chart to plot your position and Bob’s your Uncle as they say.

If you’d like to play with a sextant, come on down to the shop; we have several models in our Nautical Necessities case.