The Mariners’ Museum has a large collection of very old—to ancient navigation instruments. These include astrolabes in the Age of Exploration gallery, quadrants, cross staffs, back staffs, octants & sextants in several galleries. A reproduction of the even more primitive Kama’l can be found in the Age of Exploration Gallery, and it was one of the earliest devices to estimate the elevation of a heavenly body above the horizon. That observation put the ancients on the same track that we “modern” navigators used—until satellites, computers, and GPS made the satisfying and elegant art of celestial navigation obsolete.
The earliest astronomers through painstaking and detailed observations and record-keeping recognized that the stars seemed to rotate about a single star in the heavens, Polaris, in the constellation Ursa Minor. The ancients eventually realized that the angular elevation (altitude) of Polaris above the horizon corresponded almost exactly with the latitude on the earth from which the altitude measurement was made. From the altitude of Polaris, and a few corrections the Latitude can be easily calculated. (Corrections are necessary since Polaris is not exactly due north, in fact, because of precession of the earth’s axis, Polaris was not always and will not always be the North Star. Around 14,000 CE, the star Vega will be in that position for 500 or 1000 years.)