I have recently been working on a small display at the Royal Observatory (opening next month) called Measuring the Universe. Despite being small-scale the topic is – in every sense – vast. The Observatory’s Public Astronomer, Marek Kukula, and I are trying to cover the history of measurements of the scale of the solar system, the distance to the nearest stars, the space between galaxies and to the Cosmic Microwave Background. This takes us from the Earth to the edge of the known universe, and from Greeks to researchers today.
I have been focusing on the story of measuring the Astronomical Unit, that is the distance between the Earth and the Sun, and mainly on the use of the rare astronomical phenomenon of the transit of Venus to measure solar parallax. In 1761, 1769, 1874 and 1882 there were a huge number of observations made, across the world, motivated by the hope of establishing a scale for the workings of the Newtonian solar system, thereby improving astronomical theory and predictions, but also by a range of practical, geographical, national and imperial interests. A useful list of historic transit observations can be found here.
There are three good reasons for turning over half of the exhibition to this story: 1) there is a transit of Venus happening this June, probably the last opportunity to see it in any of our lifetimes 2) the Royal Observatory and its staff were much involved in the effort of organising expeditions, observing transits and reducing the data to produce results and 3) transit observations required overseas expeditions, as measuring solar parallax required observations from different latitudes, which involved maritime navigation, exploration and a host of themes of interest to the ROG, the NMM and me, as curator and a member of the Longitude project team.
Distilling down a story that includes Edmond Halley, Nevil Maskelyne, James Cook, George Airy and a host of the ROG’s assistants – to indicate just a few on the British side – has been challenging, to say the least! The main mission is to convey an idea of the method, the amount of organisation and effort required, the international nature of the enterprise, and the wide interest that it evoked, well beyond the scientific world. With the international story, I have tried to show that the co-operation that took place with regard to promoting expeditions and collating results was probably less significant than the national rivalries, the dangers of travelling during the war, and the selection of locations for observing that related directly to imperial and trading interests.
There are so many fascinating stories to which we cannot do justice in the available space. I am hoping to include one of the best – the sad tale of Guillaume Le Gentil - but it is impossible to explore the background fully. This includes the Seven Years’ War and, specifically, the French/British rivalry in the Indian Ocean and desire for access to India and trade routes. This military and geopolitical history does not always get enough attention in the story of longitude. Not only did overseas trade and competition provide a spur to finding a solution, the process of finding one was sometimes impeded by war (for example, when Harrison’s first timekeeper was to be tested, they were unable initially to make the journey to the West Indies required by the 1714 Act), and sometimes , of course, contributed to the extension of imperial interests – as in the voyages of Cook and those who followed.
Because the history of transit observations is wound up with that of Cook (his first voyage was a transit expedition, as well as a testing ground for the new Nautical Almanac and a mission to locate and claim the southern continent), the current interest surrounding the 2012 transit has encouraged some to think about longitude and navigation. I spotted, on The Transit of Venus site blog, a post by Nick Lomb on How Cook navigated to Tahiti. This includes a discussion of the extent to which Cook knew “his position at all times” as a result of having access to the first edition of the Nautical Almanac. This mainly focuses on the point that lunar distances won’t work in cloudy skies, but misses the fact that Cook and Charles Green (the official astronomer, and former ROG assistant) ran out of Nautical Almanac predictions over the course of the voyage and that the length of time it took to calculate position by lunar distance usually meant that the navigator would only know where he had been rather than where he currently was. Precise position for charting and, especially, for locating observers of the transit of Venus would have been carried out by observing transits of Jupiter’s satellites rather than, or as well as, lunar distances.
Readers of this blog might also be interested in the current voyage of the replica of Cook’s ship, HMB Endeavour, owned by the Australian National Maritime Museum. The crew is currently cirumnavigating Australia and will stop at Lord Howe Island (named after Richard Howe, a regular attendee of Board of Longitude meetings in the 1760s, as Treasurer of the Navy, and in the 1780s, as First Lord of the Admiralty) to observe the transit of Venus. Those on board, either for the whole circumnavigation or for the transit of Venus leg, will be learning and using 18th-century sailing and navigation techniques. I am assuming that they have 21st-century backup!
Rebekah
Would you be willing to travel to the Oxford area next term to speak to the school history/science societies about transits? We can cover travel expenses and a speaking fee if that helps I’m very keen to cross the science/history divide! If this may be possible perhaps you could e-mail? Many thanks.
Comment by Kevin Mosedale February 19, 2012 @ 2:16 pm