Return of the Sextants: Guest Post

Today we’re featuring a guest post from Sarah Pickman, a PhD student in the History Dept. at Yale. Sarah works on the history of exploration, field collecting, and natural history museums, and anthropology in nineteenth and twentieth centuries. Her past work has focused on the material culture of expeditions, from field provisions to Polar gear. Sarah comes to Yale from New York, where she earned an M.A. in Decorative Arts, Design History and Material Culture at Bard College.

Any casual observer can see that there’s a certain vogue for retro technology in the air. So dust off your home canning system, pull out your vinyl records, and break out your…sextant?


Double-bridge sextant, c. 1798. Collection of National Maritime Museum, Greenwich, UK, NAV1107

Don’t laugh. For centuries, this humble-looking triangle helped sailors of all stripes, giving them a reliable way use the location of celestial bodies above them to pinpoint their own location on the globe. In the days before GPS, sextants were a critical part of any seafarer’s kit, and could mean the difference between navigating a ship safely home or becoming hopelessly lost, left to the mercy of the ocean. In a strange twist of technological fate, this instrument is enjoying a revival of sorts.

According to an article in the Annapolis, Maryland-based Capital Gazette, the U.S. Naval Academy has reintroduced a class on celestial navigation as part of its curriculum almost two decades after the class was eliminated as outdated. Limited training in the techniques of celestial navigation, including the use of sextants, was reinstated for officers in 2011. The Academy is currently reorganizing a class for all enlisted ranks, which is expected to begin next fall. The Navy has also introduced celestial navigation to its Reserve Officers’ Training Corps (ROTC) programs on a handful of college campuses.

The Navy’s recent change-of-heart isn’t motivated by trendy nostalgia for older technology, though. It’s prompted by fears that the satellite-based Global Positioning System, used since 1995 to pinpoint ships’ locations might be vulnerable to cyberattacks. The Capital Gazette article quotes the Academy’s Lieutenant Commander Ryan Rogers, who holds the excellent title of Deputy Chairman of Seamanship and Navigation, as saying “We went away from celestial navigation because computers are great. The problem is, there’s no backup…We know there are cyber vulnerabilities [with GPS].” The Navy fears that it might be possible for someone or some group to hack into the Navy’s GPS-reliant navigation programs, potentially stranding Naval vessels all over the world.

The sextant, by contrast, isn’t vulnerable to hacking. And using one is fairly straightforward. Put simply, sextants measure the angle between two visible objects. This measurement, along with the time of day that the reading was taken, can be located on tables in premade nautical charts or almanacs to help fix the ship’s position. Measuring the angle between the sun at noon and the horizon can determine latitude, for example, while the angle between the moon and a star or planet can fix a ship’s longitude.

sextant animation

Joaquim Alves Gaspar, Wikimedia Commons

The sextant wasn’t the only way to navigate before satellites–different techniques of celestial navigation have existed in many cultures across time and space. For thousands of years, sailors from the Pacific to the Mediterranean relied on observations of stars’ movements, among other natural phenomena, to help guide them at sea. For example, ancient Polynesians likely navigated to far-flung islands with the help of zenith stars: stars that pass directly overhead at identifiable locations, such as the star known today as Sirius, the zenith star at the latitude of Tahiti. The sextant in its current form emerged only in the eighteenth century (English mathematician John Hadley and Philadelphia-based glazier Thomas Godfrey both laid claim to the invention), and was preceded by other navigational instruments such as the cross staff, mariner’s astrolabe and backstaff. However, the sextant quickly became the sailors’ favored tool: it was precise and unlike earlier navigational aids could be used both day and night.

This instrument has undoubtedly been the salvation of many lost and desperate ships’ crews. One of the most dramatic examples of a sextant in action was the voyage of the James Caird, the twenty-three foot wooden lifeboat that was part of Ernest Shackleton’s doomed Antarctic expedition of 1914-1917. After Shackleton and his twenty-seven man crew were stranded on an island off the Antarctic coast, the explorer and five others sailed the James Caird 800 nautical miles through some of the roughest seas on earth to find help. They carried with them a Heath & Co. “Hezzanith” sextant, today on display at the Scott Polar Research Institute at the University of Cambridge.

The launch of the James Caird from Elephant Island, 1916. Collection of Scott Polar Research Institute, Cambridge, P66/18/16

The launch of the James Caird from Elephant Island, 1916. Collection of Scott Polar Research Institute, Cambridge, P66/18/16

Shackleton's navigational instruments on view at Scott Polar Research Institute. Photo by Mark Brandon, Seb Coulthard Expeditions.

Shackleton’s navigational instruments on view at Scott Polar Research Institute. Photo by Mark Brandon, Seb Coulthard Expeditions.

Even with such an impressive pedigree, it’s easy to understand why satellite-based navigation supplanted the sextant. Since sextants require two visible objects for readings, they’re fairly useless in very foggy conditions common at sea. At its most accurate, the sextant and nautical tables can pinpoint a ship’s location to within a mile and a half, which is impressive, except that GPS can whittle that figure down to a matter of feet. Today, sextants are still manufactured by firms like the Annapolis-based Weems & Plath, but are mostly purchased by private cruising sailors as a backup in case of damage to their boats’ GPS receivers.

Still, if the U.S. Naval Academy is any indication, this piece of analog technology may yet prove its worth in the digital age. At the very least, its reintroduction provides some food for thought as a reminder of what can be gained–as well as lost–with the introduction of new technology. Celestial navigation is one of the oldest wayfinding methods in human history; practiced across centuries and across the globe, yet rendered almost obsolete in a matter of decades. And even more prosaic forms of navigation, like the humble folding road map, have fallen in popularity in the age of satellite navigation. Now faced with possible vulnerabilities in its GPS systems, the U.S. Navy has the additional challenge of trying to rebuild knowledge of another navigation method within its ranks. This dilemma challenges the idea that every technological advancement is a clear step forward. GPS is extremely accurate and easy to use. But perhaps a little independence from it – or at the very least, knowledge of other ways to get around – can be a good thing now and then. As anyone who has relied on Google Maps to find his or her way, only to be stranded by a poor cellular or wifi connection can attest, not having a substitute method for navigating can leave you feeling lost at sea.[1]

[1] The author is guilty as charged.

1 thought on “Return of the Sextants: Guest Post

  1. Evan Hepler-Smith


    Thanks for this post. Fascinating stuff! It makes me wonder – we’ve become familiar with stories of the role of military research and warfare in technological change. But clearly military preparations for catastrophic exigencies can serve to maintain technologies as well. I’m curious – in the field of navigation or elsewhere, have you come across other examples of military-driven maintenance of systems and tools that might otherwise have (or actually had) fallen into obsolescence?




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