~ Exploring the 19th Century ~

The main aim for astronomers in the 19^th Century was to reduce the uncertainty of the Astronomical Unit. Imagine this: a difference of error of one-hundredth of an arc-second would result in a difference of 100 000 miles. Basically, by reducing the uncertainty in the AU, scientists had hoped to make the scale of our solar system more accurate by about several million miles.

Since the black drop affect had resulted in bad results in the past, scientists had to find ways to overcome the problem. Astronomer Simon Newcomb from the USA, who overlooked 8 expeditions carried out by the USA for the 1874 Transit of Venus, proposed a new method of observing the Transit. He said that instead of recoding the times of contact between Venus and the Sun, which were obscured by the black drop affect, a better way might be to observe the positions of Venus in relation to the Sun, during the Transit. Unfortunately, no results were published by Simon Newcomb and his eight teams regarding the Transit of 1874.

Another astronomer, William Harknesss, carried on Newcomb’s idea by using photography to record the positions of Venus. Yet poor results from the first transit of the pair, left the international community divided; with American astronomers supporting photography as a means of observation and most of the Europeans (bar the French) condemning it. And so, the phenomenon in 1882 was observed by cameras held by the French and the Americans, and timings were measured with the help of heliometers in most Europeans organizations.

Almost six years later (after the second transit in the pair), William Harkness processed the data to produce that value of the AU as: 92 797 000 miles with an error of 59,700 miles

In 1891, Simon Newcomb used the same data, but with better analysis techniques derived the value of the Earth-Sun distance as: 149.59±0.31 million kilometres

In the end, after many centuries of frustration, the black drop affect was never completely overcome. It was only radar instruments that were invented in the 20^th Century that allowed us to obtain the most precise measurement of the Astronomical Unit, with is modern value being:

149,597,870.691±0.030 kilometres

And yes, the AU is really known to the precision of 30 metres.

The level of perseverance and innovation among scientists throughout history was allowed to shine through because of the Transit of Venus, and the challenge that it presented. Its scientific importance was huge, as it allowed us to obtain a very valuable quantity: the Astronomical Unit. Astronomers around the globe were united in their efforts, and a large scale international cooperation was witnessed, as man launched a quest to establish the scale of our universe. Not only that, cultures were allowed to meet and legendary voyages, like that of Captain James Cook, influenced the world, and have affected the composition of its people today. Finally, the Earth-Sun distance is a cornerstone for all areas of astronomy, and it has allowed us to continue further research and exploration into space and beyond.

The rare phenomenon of Venus in Transit has truly affected mankind’s global history in many diverse ways.

So the question is begged: what do YOU expect in 2004?