Sight of the century
By Dr Nick Lomb (BSc ’69 PhD ’75)
The upcoming transit of Venus in June will not take place again for more than 100 years, so take your pews to witness this astronomical event – which is of particular importance to the history of Australia.
On the morning of Wednesday 9 December 1874 Henry Chamberlain Russell, director of Sydney Observatory, was waiting for the planet Venus to start moving across the Sun. Russell had graduated in 1859 from the University of Sydney, where he had received the Deas-Thomson scholarship, which is still awarded today to the student “who demonstrates the greatest proficiency in Senior Physics”. Many years after the transit, in 1891, Russell was appointed as the University’s first Australian-born Vice-Chancellor. (His daughter Jane Foss Russell was also to have strong links to the University, links that were recently commemorated by naming a new building on the University campus in her honour.)
The upcoming transit of Venus is an astronomical event of particular importance to the history of Australia
Russell had prepared carefully for the 1874 transit. He had equipped the Observatory with new modern instruments and, to insure against cloud disrupting observations, he had set up observing stations at Woodford in the Blue Mountains, Eden on the South Coast and Goulburn in the Southern Tablelands. To staff these three country stations, Russell had recruited the best scientific men in the colony, including Archibald Liversidge,
the newly appointed Professor of
Geology and Mineralogy at the University.
The 1874 transit and the following one in 1882 were two of the most important events in 19th-century astronomy, just as the transits of 1761 and 1769 were in the 18th century. They were important as they provided a way of measuring the distance between the Earth and the Sun. This was the key distance that astronomers needed to work out the scale of the Solar System and to establish the distances to the nearest stars. The idea was to time the instants when Venus just appeared to touch the inside edge of the Sun at the beginning and at the end of the transit.
Captain Cook's despondency
If the timing could be done accurately, astronomers could compare observations from widely separated places and determine the sought-for distance using simple trigonometry. However, various atmospheric effects, the best known of which is called the “black drop”, made timing difficult. James Cook, who observed the 1769 transit from the Pacific island of Tahiti, was despondent that his times differed slightly from those of the two other observers with him. He was not to know that observers elsewhere in the world had experienced similar problems and that the observations from Tahiti were better than most.
After completing the necessary observations in Tahiti, Cook opened sealed orders to search for “Terra Australis Incognita” or the “Unknown Southern Land”. Not finding this mythical land, he decided to return home by sailing towards the unexplored east coast of what was then known as New Holland. Mapping New Zealand on the way, he reached Australia, named it New South Wales and followed its coast northward, charting it as he went. This first visit by Europeans to the eastern part of the continent was to have far-reaching consequences, for it led directly to the arrival of the First Fleet in 1788 and British settlement.
Due to the consequent importance of transits of Venus in the history of the country, it was fitting that the next transit after that witnessed by Cook was so well observed from Australia. In addition to Russell and his team in NSW, there was a similar team in Victoria and observations from South Australia plus two separate teams of American observers in Tasmania.
Russell and the other New South Wales observers were fortunate in having generally clear skies and made excellent observations of the transit. A few months later, Russell gathered up the observations and photographs taken during the event and personally delivered them to the Astronomer Royal at Greenwich in the UK. He also collated the results into a beautifully illustrated book that was published 18 years after the event. The long delay was probably due to an oversight by the Government Printer.
Russell’s book, Observations of the Transit of Venus, 9 December 1874, is so well known around the world that almost every article or book that is published about the transits today includes illustrations from it. It was this book that triggered my own interest in transits of Venus, for it was one of the first Observatory publications that I was shown when I started work at Sydney Observatory in 1979. While preparing an exhibition on transits of Venus in 2004, I was excited to find the original illustrations for the book in the archives kept at State Records. These originals became the highlights of the exhibition, although for conservation reasons each illustration could only be shown for a relatively short time.
On seeing that the original illustrations were even more striking than the photolithographs of them that had appeared in the book, I became keen to make them more widely accessible. Eventually, NewSouth Books took up the idea and the new publication expanded to become the full history of transits called Transit of Venus: 1631 to the Present. This book takes the story from the first sighting of a transit by the young Englishman Jeremiah Horrocks in 1631 to the widely observed 2004 transit.
Now there is a new transit of Venus coming up on Wednesday 6 June (5 June in the USA). As the following transit is not until 2117, this will be the last opportunity for anyone alive to see one of the rarest and most famous astronomical events. Australia and New Zealand will be among the best places from which to view the 2012 transit as, clouds permitting, it will be visible from beginning to end from most of the two countries. From Sydney the transit begins at 8:16am and ends at 2:44pm AEST, with similar times elsewhere in Australia, and New Zealand, after allowing for different time zones. From Perth the transit will already be in progress at sunrise.
After observing the 1769 transit from Tahiti, Captain Cook opened sealed orders to search for the Unknown Southern Land
The entire transit will also be visible from New Guinea, Japan, Korea and the eastern parts of China and the Russian Federation. It will also be fully visible from Hawaii and Alaska, while from the rest of the USA the transit will still be in progress at sunset. From Europe (apart from parts of Spain and Portugal), the Middle East, eastern parts of Africa, India and Indonesia the transit will already be in progress at sunrise.
However, although there is something exciting going on in the direction of the Sun on 6 June, it needs to be emphasised that looking at the Sun is highly dangerous. Serious and irreparable eye damage can occur from viewing the Sun with the unaided eye or, even worse, through binoculars or a telescope. For safe viewing go to your nearest public observatory, such as Sydney Observatory, or check whether a local amateur astronomy group has arranged a public viewing of the event.
Whichever way you do it, do not miss the 2012 transit, because you will not have another chance!