Voyages of Heavenly Discovery: Eclipse Expeditions

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.

Some were positively cooperative.  In 1842, astronomers did not have to travel to observe an eclipse–the eclipse was coming to them, as the path of totality crossed the European continent.  Careful timing of the eclipse would enable more precise determination of the longitudes of cities across Europe, thus uniting the various European countries, at least cartographically. On the astronomical side, British astronomer Francis Baily, observing from Italy, noticed three red prominences inside the usual brilliant white corona of the eclipsed Sun.  What these were, and whether they belonged to the Sun or the Moon were questions that astronomers would eagerly await the next eclipses to answer.


Drawing of prominences during the total solar eclipse of 1842.

The mounting of an eclipse expedition was an exercise in logistics, involving accurate calculation of the path of totality, determining the site along the path with the best odds for clear skies, collecting and sometimes fabricating portable precision optical instruments, and organizing the transportation of men and materiel to the site with sufficient time to set up and calibrate the instruments before the day of the eclipse. Some expeditions brought along prefabricated buildings.  Others operated under more primitive conditions and brought home only their data and the expensive bits of their instrumentation, leaving the rest behind.  No wonder that most expeditions were run under the auspices of major scientific organization such as the Royal Society, the Smithsonian Institute, and the University of California.

Eclipse_01 India

British astronomers in India to observe the eclipse of 1870.

Still, the best laid plans…In 1878, an eclipse was to pass through the Rocky Mountains. An expedition was planned for the summit of Pike’s Peak (14,100 feet, 4300 m) as the idea that mountaintops were ideal sites for observatories was just catching on. After traveling the 18-mile road to the peak, the expedition discovered that the US Signal Service station at the summit had never received orders notifying them of expedition’s arrival.  Consequently, the astronomers and their ton of equipment were relegated to tents which were little protection again the snow, rain, and wind.  In the end, however, the astronomers observed unprecedented detail of the Sun’s corona which showed it to be much larger than previously believed.  Interestingly, a young Thomas Edison was traveling with another expedition in Wyoming to test his new invention to measure changes in heat, the tasimeter. It failed.


Drawing of the eclipsed sun from Caroline Island in the south Pacific in 1883.

Lick Observatory of the University of California (my home town observatory, perched on Mount Hamilton overlooking San Jose) organized a number of expeditions.  Perhaps the most ambitious was the 1883 expedition to Caroline Island, a tiny atoll in what is now the Republic of Kiribati in the South Pacific. Upon reaching the island, it was discovered that the ship could not penetrate the shallow reef, requiring all equipment and supplies to be carried by hand almost a half mile to the camp location. The scientists took advantage of the crew’s hard work hauling though.  Besides eclipse observations, a detailed map of the island was drawn up, meteorological and sea water composition records were kept, and an exhaustive list of the flora and fauna of the island was compiled. The observers also made a diligent search for the planet Vulcan, which was hypothesized to exist within the orbit of Mercury and to exert a gravitational tug on Mercury, displacing it just slightly from where calculations said it should be.  Alas, the report by Professor Edward Holden, the leader of the expeditions stated in his official report, “…I must regard the fact of the non-existence of Vulcan as definitively settled by Dr. Palisa’s observations and my own.”

Yet it was not to be the end of heavenly bodies tending to be not exactly where we expect them to be. One of the predictions of Einstein’s 1915 Theory of General Relativity is that light should be bent by the gravitational force exerted by massive objects.  A solar eclipse is the perfect circumstance to detect such an effect as stars can be observed very near to a large object (the Sun).  Careful measurement of their exact positions could confirm this prediction of Einstein’s theory.

Unfortunately, World War I and the Russian Revolutions happened, which made traveling across the globe both logistically and politically difficult.  After the war ended, the British hurriedly launched two expeditions to Brazil and West Africa to take precision photographs of the stars near the eclipsed sun. After careful measurement of the plates, Einstein’s theory was found true. That British astronomers confirmed the theory of a German scientist helped heal the wounds of war in the scientific community.

- Einstein and Eddington. German-born physicist Albert Einstein (1879-1955), at left, was famous for his theories of relativity. British astrophysicist Sir Arthur Eddington (1882-1944), at right, pionee -

Albert Einstein and Sir Arthur Eddington, director of the eclipse expedition of 1919 that confirmed that gravity can bend light as described in Einstein’s General Theory of Relativity

I’ve outlined just a few of the very many eclipse expeditions mounted by many countries over the years, especially during the 18th century.  Still, it should be remembered that the cumulative time of totality studied by all these expeditions barely total to an hour or two over a couple of centuries. That’s a real long-term investment in basic science!

This year’s eclipse won’t require a massive undertaking to witness, especially if you are close to the path of totality which stretches from Pacific to Atlantic shores across the middle of the US. My wife and I will be driving up to Madras, Oregon and will be camping along with, it seems, many others in the path of totality in an area that has pretty good odds to have clear skies. I have already experienced one total solar eclipse in Aruba in 1998, and it was an amazing experience.  When the moment of totality hits, and the sun disappears and is replaced by this strange circular thing in the sky, some primitive part of the brain stops and says “The sun’s gone away. That’s not right.” I hope I have enough wits about me to remember all those astronomers that have come before and under sometimes dire circumstances gained knowledge about how our little corner of the Universe works.



I would be remiss if I didn’t acknowledge one source that I found both interesting and useful in composing this blog post: an article titled “The Victorian Space Program” by Trudy E. Bell which was published in the Spring 2003 issue of The Bent of Tau Beta Pi.



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