The Mariner’s Astrolabe

Since the inception of the MFMHS, the mariner’s astrolabe has served as its logo. This is an apt symbol for an organization specializing in the study of colonial maritime culture, especially when the 1622 wreck of Nuestra Señora de Atocha has yielded five astrolabes, and the Santa Margarita one, constituting the largest single collection from a specific period. Such a large group, from only two ships, makes it clear that there was a strong reliance on astrolabes by ships of the early 17th century, but how many people really know anything about them? What exactly did they do? How were they used? The answer is really quite simple; with these beautifully crafted instruments, pilots measured the angle of the sun from either the zenith or the horizon; a measurement that could then be used to determine the ship’s latitude, and its position in the vast expanse of the sea. The mariner’s astrolabe was derived from the more complex planispheric astrolabe, which was used by early astronomers to calculate the movements of the heavens. The Portuguese school of navigation, founded in the 15th century to find an eastern route to the Orient, worked to develop simpler instruments, which could be used easily by relatively uneducated seamen. At first, the angle of the northern, Pole star was measured to determine latitude, but in 1471 the equator was reached, where this star could no longer be seen. New methods needed to be developed to successfully negotiate the southern seas