A transit of Venus takes place when the planet crosses the disc of the Sun as seen from Earth. Such transits occur in pairs eight years apart, separated by a century or so. To astronomers of the 18th and 19th centuries they were of crucial importance as they provided a method of determining the distance between the Earth and Sun, and hence the scale of the Solar System.

Australia has a close connection with this rare astronomical event through Captain James Cook who mapped the continent’s east coast on his way back to Britain after observing the transit of 1769 from Tahiti. When the next transit occurred in 1874, Sydney Observatory was in an ideal position to make detailed observations.

Henry Chamberlain Russell started preparing for the 1874 transit immediately on becoming Government Astronomer in 1870. He purchased new telescopes and recruited a team of observers. Among them were the Reverend W. Scott, the first Government Astronomer, Philip F Adams, the Surveyor-General, Professor Archibald Liversidge who helped to establish the museum that eventually became the Powerhouse and the instrument maker Angelo Tornaghi. These observers went to a number of observing stations scattered around New South Wales - Sydney Observatory itself, Eden, Goulburn and Woodford in the Blue Mountains - so as to maximise the chance of getting a clear sky at least at one site.

On the day of the transit the weather was fine at all locations except at Eden on the south coast. Russell wrote that, ’Never perhaps in the world’s history, did morning dawn on so many waiting astronomers as it did on the 9th of December, 1874’. Although atmospheric effects such as shading between the edge of the planet and the Sun made observing difficult, good results were obtained.

After the transit Russell left for England, taking with him the reports and observations of all his observers. These he handed to the Astronomer Royal who was arranging the analysis of all the observations made in the British Empire. Many years later, in 1892, Russell published a beautifully illustrated book with the complete details of all the observations that he and his observers had made.
Nick Lomb
Observer & observed: a pictorial history of Sydney Observatory and Observatory Hill, Powerhouse Publishing, Sydney, 2001.

© Powerhouse Publishing, Sydney, 2001

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