Sextant: data and historical old ship GPS navigation

Continuing from our last post on models of historic civilizations and data, we’re drawing a line from Carl Sagan to the Conquistadors (and modern TV documentaries’ theories about them). This historic photo is an antique sextant from 1890. This historical navigation device worked by measuring the angle between the sun (or stars) and horizon using two mirrors. It was the GPS (or Apple Maps) of its day. And, as we learned from Apple Map’s initial glitches, then as now, successful navigation required a lot of information (or data) to work correctly! Since the Internet didn’t exist, this data had to arrive by some other means, which we’ll talk about in a future post.

(So we’re also continuing on our earlier mirror theme.) The use of two mirrors’ reflection to align the image of the object with the horizon (when the sextant was set at the correct angle) enabled accurate measurements when on a moving platform, such as by a sailor on a boat at sea. The concept of a two-mirror navigational aid was invented by none other than Issac Newton. (This makes it a little late for our conquistadors, however…. More on that in the future.)

It’s complicated getting a position from the device. It generally requires having an accurate time, using mathematical tables, or taking multiple measurements over time (or some combination of these together).

Now you know why they no longer use these much now that GPS is here! It’s the latter — mathematical tables and following complex recipes — that are interesting in our continuing story of data science and civilization.

A version of this article originally appeared as a photo post on our Instagram feed.

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