Transit of Venus: a must-see for everyone ... no seriously
By Duncan Steel, University of New South Wales
Taking inspiration from this rather strong suggestion that some notable events justify the interruption of “work as usual”, I’ll take the liberty of suggesting that any Minister of Education who does not instruct school principals and teachers to interrupt normal curriculum next Wednesday is also a bum. Indeed, they might just be unfit for office.
The event that will occur on June 6 is far more significant than the mere winning of a yacht race and in educational terms it’s hugely more valuable.
An article on The Conversation by Helen Maynard-Casely has already given some information about its background and significance, but there’s far more to be said and learned. I am talking about the transit of Venus across the face of the sun.
Rather conveniently, the transit will be visible throughout Australia and New Zealand, and it occurs right across the time of day when kids are at school. From the east of Australia the entire transit can be seen, lasting for more than six hours.
(In Western Australia the transit will already have begun at sunrise, but that matters little.)
I am not suggesting that anyone should watch the whole thing. What I am suggesting is that everyone should take a peek for a minute or two, and reflect on the transit’s special significance. If such infrequent events did not take place, we probably wouldn’t speak English, nor play cricket.
This should not be regarded as a distraction from the rigid school curriculum, but rather as a multifaceted opportunity to boost the education of our children. It should also be seen as an opportunity for all Australians and New Zealanders to reflect on how their countries became members of the eventual British Commonwealth.
Let me make a few pertinent points, and I’ll let you, dear reader, ponder which of them have significance with regard to many different academic and practical subjects:
James Cook mapped New Zealand and the east coast of Australia, and claimed them for the Crown, as part of his first Pacific expedition in 1768-1771. The primary aim of the expedition was the observation of the transit of Venus from Tahiti in June 1769.
Subjects: history, astronomy, legal studies – was Australia really terra nullius (no-man’s land)?
Cook and colleagues were sent to observe the transit because English astronomer Edmond Halley had suggested, decades before, that it would lead to a better evaluation of the distance to the sun (the Astronomical Unit, or AU).
From that, astronomers and mathematicians would be able to calculate better tables of future positions of the moon, from which seafarers would be able to tell the time and their longitude.
Subjects: mathematics, physics, geography, navigation and mapping.
Although it is often said that Cook needed to travel to the far side of the globe because the transit could not be seen from Europe, that’s incorrect. The transit was shortly before the northern summer solstice, meaning it could be witnessed in its entirety above the Arctic Circle.
The British also sent expeditions to Norway and Canada. King George III saw part of the transit from Richmond, west of London. The French went to Baja California, in the face of Spanish opposition in the Philippines, and also to their Indian Ocean territories.
Cook was sent south, so as to get the parallax for an extreme chord (a straight line joining the ends of an arc) across the face of the sun.
Subjects: geometry, mapping, surveying, seasons and climate.
In 1761 the many transit of Venus expeditions had failed to render useful data with regard to the late Edmond Halley’s concept.
Lesson: don’t be discouraged by your failures – keep trying!
The observations from Cook’s 1769 expedition weren’t accurate enough to fulfil Halley’s requirements either.
Lesson: huge positive returns can be derived from scientific and other high-cost projects even if the original aim fails.
It was three years before Cook returned to England. Many of his men died on the voyage, others were away for longer. The French aristocrat Guillaume Le Gentil was absent from his home country for 11 years, was declared deceased in his absence, and failed to get useful observations in both 1761 and 1769.
However, he did complete invaluable natural history studies in Mauritius and Madagascar.
Subjects: botany, zoology, geology and anthropology.
As a result of Cook’s arrival in Australia, many places here have linked names: Botany Bay with Cape Solander at its entrance, Cooktown and Green Island in Far North Queensland, and many places both in between and further north and south.
Subjects: botany, zoology, geography, geology and history.
Cook lost only a few men to scurvy in 1768-71, his methods of tackling it leading to great improvements in the understanding of the causes of that disease and others.
Subjects: medicine, nutrition and physiology.
There were orders from Cook’s superiors at the Admiralty in London, in a sealed envelope not to be opened until after the transit had passed, instructing him to search for “Terra Australis Incognita”, the great unknown southern land that was believed to exist.
We all know what happened as a result.
Lesson: the stated objective of any human quest may not be the only intent, any more than the Apollo program had a sole aim of letting a few astronauts stroll across the lunar surface.
Two other British transit observers were Charles Mason and Jeremiah Dixon. In the mid-1760s, between transits, they surveyed the eponymous Mason-Dixon Line which divides the United States into north and south.
Subject: history of the American Civil War and the abolition of slavery.
The next transits of Venus occurred in 1874 and 1882, and were also closely observed. In 1874 Russia alone sent out 26 expeditions, Britain a dozen, the United States eight, France and Germany six each, Italy three and the Netherlands just one.
Good geographical coverage was needed, but since the transit was in December there was a better chance of getting clear skies in the southern hemisphere. As a result, the British sent expeditions to Christchurch in New Zealand, a variety of locations in south-eastern Australia – including the newly-built Sydney Observatory – and several other locations.
The Americans sent expeditions to Beijing (then called Peking), Vladivostok and Nagasaki in the northern hemisphere, to Bluff, Queenstown, the Chatham Islands and several other locations in New Zealand, to Hobart in Tasmania, and even to the windswept Kerguelen Island in the Indian Ocean.
French expeditions went to places such as New Caledonia and Campbell Island and a German expedition went to the Auckland Islands.
Using the data gathered from these observations, the Canadian-American astronomer Simon Newcomb calculated a value for the distance to the sun of 149.59 ± 0.31 million kilometres, a precision of one part in 480.
This was more or less in line with what Edmond Halley had expected almost two centuries before: that a determination of the solar distance to one part in 500 would be feasible.
By that time, however, there was no longer any need for the lunar tables that had been Halley’s main motivation.
Indeed on his second and third voyages to the Pacific, James Cook had used marine chronometers and sworn by them as the best way to navigate.
In view of the fact I have written above about various spin-offs from the transit of Venus expeditions, there is one final point I might mention.
One big difference from the 18th century observations of Cook and others and those of the 19th century was the advent of photography. Jules Janssen, a Frenchman who observed both the 1874 and 1882 transits, invented a circular glass photographic plate with which, during a transit, he could take up to 60 pictures of the sun – one every second – using a small clockwork mechanism to drive the plate around.
Later, the famous inventor Thomas Edison met Janssen and viewed this apparatus, and it inspired him in the development of the movie camera.
The whole history of the movies was changed by the fact Edison saw how to make a movie camera using a technique developed in order to make measurements of a transit of Venus.
In modern times Venus has been used in a totally different way to get a very precise value for the Astronomical Unit. By bouncing radar pulses off the planet, astronomers have been able to measure its distance from Earth, and then determine the distance from Earth to the sun. By this and other high-tech methods, the modern-day value for the AU has been determined: 149,597,870,700 ± 3 metres.
When Venus slowly edges its way across the face of the sun on Wednesday June 6, I believe everyone should take a peek. Not directly, and certainly not through a telescope or binoculars, but rather using one of the many safe ways of viewing the sun, including eclipse glasses if you have them or projecting an image with a telescope on to a screen.
The simplest way is with a mirror: tape cardboard over all of the mirror except for a square about five or six millimetres wide. Reflect an image of the sun on to a suitable screen several metres away (such as a white ceiling or a piece of paper). The round solar image will be several centimetres across.
That will show you the black blob of Venus in transit, about 4% of the diameter of the sun. It’s your last chance: the next transit of Venus won’t occur until 2117.
So, why not watch it on the evening news, or the internet? I’ll tell you: compare the experiences of watching a football game at home on TV, and at the stadium. The former is more comfortable, and you get a better view. The latter is an entirely different experience, and far more memorable.
Most people only remember ten or 20 distinct days from their schooling, the rest being merged together into a fuzzy whole. The transit of Venus on June 6 should be one day that students never forget.
An upcoming transit – Helen Maynard-Casely
Duncan Steel does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.