A transit of Venus occurs when the planet Venus passes directly between the sun and the earth. From the earth, Venus can be seen as a tiny black disc moving across the face of the sun. Transits come in pairs, eight years apart, then there is a gap of 105 years. Past observations of the transit of Venus helped astronomers calculate the distance between the sun and the earth.
The 1882 transit of Venus was an event of great excitement to the small New Zealand scientific community. Under the leadership of James Hector (director of the colonial museum) and James McKerrow (surveyor general), plans were developed for a network of official observers, all linked together by telegraph to give accurate timing. Every high-quality telescope in the country was pressed into service, and the following were designated official sites:
- Colonial Observatory, Wellington (Archdeacon Stock and T. King)
- Mt Cook, Wellington (J. McKerrow and C. W. Adams)
- Wairarapa (J. W. A. Marchant and Captain Hewitt)
- New Plymouth (Mr Humphries)
- Nelson (A. S. Atkinson)
- Christchurch (J. Townsend and W. Kitson)
- Timaru (Archdeacon Harper)
- Dunedin (R. Gillies, A. Beverley and H. Skey)
- Clyde (J. Hector).
Most of the observers lived nearby, but Hector travelled from Wellington to Clyde with his equipment. Perhaps he thought that he would have a better chance of success in the clear skies of central Otago, as his attempt to view the 1874 transit in Wellington had been spoiled by bad weather. He took with him a 6-inch Cook telescope, one of the largest then available in New Zealand, loaned by G. V. Shannon. His own smaller telescope was left behind to be used by the team at the Colonial Observatory.
The transit was observed all round the globe, and there were two visiting scientific groups who brought their own equipment to New Zealand. The British expedition, under Colonel Tupman, re-occupied quarters at Burnham, near Christchurch, where the 1874 transit had been observed, and the American expedition established an observatory in the Auckland Domain, now covered by the Auckland Museum.
We are fortunate to have a record of Hector’s preparations in a letter he wrote to his wife as well as a photograph, both held in the Hocken Library, Dunedin.
Hector arrived at Clyde with his gear at least a week before the transit, and established his temporary observatory. He had to survey the location, get telegraph wires run in from the nearby telegraph station, and train his assistants in the routine he needed to follow. There were plenty of visitors every night who wanted to look at the sky through the big telescope. One night Hector gave a public lecture to an audience of about 200, with diagrams sketched on large sheets of calico.
Transit day was fine over most of New Zealand, and the Evening Post of 7 December 1882 reported an almost unqualified success for the New Zealand observations: ‘The only failure among the more important observations was that of Dr Hector at Clyde, whose view was vexatiously intercepted by a dense cloud almost at the very instant of contact. There are, however, amply sufficient complete observations for all the purposes aimed at, and the 7 December 1882 will long stand as a red letter day in the annals of astronomy.’
Hector must have been bitterly disappointed, but later that day he telegraphed Mr Shannon: ‘Sorry lost observation by one minute through a small dark cloud getting in the way: glad you saw well. Your telescope was admirable. I saw Venus atmosphere off the sun.’
Acknowledgements: Many thanks to the Hocken librarian for permission to reproduce the photograph, and for information from the Hector papers.