The upcoming total solar eclipse prompted me to look into the grand history of scientific expeditions, specifically expeditions to observe rare astronomical events.

Captain Cook’s observatory on Tahiti. Note the carefully mounted long-case clock.

One of the first voyages of discovery was to the newly discovered island of Tahiti (well, at least new to Europeans, the Tahitians obviously already knew it existed) on a ship called HMS Endeavour captained by a young Royal Navy Lieutenant by the name of James Cook.  The purpose of the voyage (at least publicly…) was to observe the Transit of Venus of 1769, that is, to watch and accurately time the planet Venus crossing in front of the sun. The ship’s company also included Joseph Banks, the famed botanist who brought along with him several assistants, two artists, and two servants.  Charles Green was appointed by the Royal Society to by one of the ship’s astronomers, the other being Cook himself who was a skilled observer.

And why all this expense to travel to the other side of the globe to observe one arcane astronomical event? The public reason was to improve navigation, specifically determination of longitude.  While the latitude of a ship at sea was easily determined with a sextant and a sunny noon-time, longitude was more difficult.  By comparing the times of the Transit of Venus at various places across the globe–some of whose positions were already accurately known, the longitudes of the observing sites could be determined with greater precision. (The longitude problem was eventually solved by John Harrison and his marine chronometers.)

So the Endeavour reached Tahiti, they timed the Transit, and then Cook opened his second set of sealed orders which essentially said, “Go look for this Terra Australis we keep hearing about, and if you find it, claim it for Britain.” After completely mapping the coast of New Zealand, Cook sailed a bit further west and found Australia.

Later astronomical expeditions were somewhat less imperialistic.

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