Astronomical tent observatories: relics of a bygone era

Between the mid-eighteenth and mid-nineteenth centuries, long-haul oceanic voyages of exploration and discovery routinely carried astronomical tent observatories to support land-based longitude determinations using heavy and cumbersome astronomical regulators and transit telescopes. Following James Cook's deployment of a pilot tent observatory on his first voyage to the Pacific in 1768-1771, the tent design was altered by William Bayly for more convenient use on Cook's second and third voyages to the Pacific. Bayly's design became the standard structure of tent observatories assigned to shipboard astronomers during the Age of Sail. By the middle of the nineteenth century, a subtle shift in focus had occurred, with tent observatories now being deployed to observe specific celestial events (such as the 1882 Venus transit or a variety of eclipses), while longitude determinations increasingly relied on the novel, compact and improved box chronometers of the day. A further shift in the application of tent observatories occurred towards the end of the nineteenth century, when astronomical applications largely gave way to a renewed focus on meteorological measurements.