When the world discovered the sun
On Jun 5 2012 I had the opportunity to witness one the rarest of astronomical events, the transit of Venus across the sun. This event only occurs twice each century eight years apart. The Venus transit will not occur again for another 108 years! Fortunately for me I witnessed the transit from a field only a few miles away at the University of South Carolina – Aiken. However, I did share one aspect with 18th century astronomers – the fickle nature of cloud cover!
The early purpose of accurately measuring the Venus transit was to derive the distance between the earth and the sun. The transit uses the optical effect of parallax and some heavenly geometry. This distance is known as the Astronomical Unit and is the measure of relative distance for the entire solar system. Thus, knowing the AU accrately means unlocking distances to all the planets! However, even today, the Venus transit is helping us develop techniques necessary for exoplanet discovery.
In his book The Day the World DIscovered the Sun Mark Anderson takes us on mankind’s first big science project of a global scale. This is the journey of three international teams to view the Venus transit in 1769 from the wilds of northern Norway, Baja Mexico and Tahiti. Maximum distance between observing points increasing the measurement accuracy. Anderson does an excellent job of portraying the hardships these teams faced including long sea voyages, waring European nations and disease that claim many of the team members. Despite all of the hardships, elementary navigation (clock-based longitude determination is decades away from common usage) and simple instruments; these teams achieved an accuracy of 99.8 percent the earth – sun distance (1 AU).
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Posted: July 5th, 2013 under Books.