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Tonight if you are lucky and the sky doesn't cloud up, you will be able to observe one of astronomy’s rare celestial events, the transit of Venus. But be careful, and don't look directly at the sun without using safe viewing glasses or lenses. If you don't own those, you can attend one of the free events listed below. If you miss tonight's transit, alas, you won’t catch another in your lifetime because the next one won’t occur until 2117.
I’ve been reading about the transit of Venus and how an earlier one in the 18th century really expanded our knowledge of the solar system. It also was the earliest example of a large and cooperative international scientific expedition.
We have two new books that report on this scientific quest. Andrea Wulf's Chasing Venus: the Race to Measure the Heavens reports on the work and incredible adventures that were undertaken by scientists worldwide in trying to observe and make measurements for the transit that occurred on June 6, 1761. In an age when it took several months for a letter to cross the oceans and a few more months for a response, a scientist in England organized this great scientific undertaking. In remote corners of the world, scientists from Britain, Russia, India, Germany, the American colonies, and Sweden set up observatories. The plan was to calculate the earth’s distance from the sun and the size of our solar system by observing Venus crossing the sun from various locations around the world.
The Day the World Discovered the Sun by Mark Anderson focuses on three of the astronomical expeditions that were focused on 1769, the following transit (two occur only eight years apart and then there is a hundred-plus year gap before the next): James Cook’s to Tahiti, the French astronomer Jean-Baptiste Chappe d'Auteroche's on La Concepción to the Gulf of California, and the Hungarian Maximilian Hell's to the Arctic Circle on the Urania.
Some astronomers had to cross through war zones. They carried letters begging the soldiers to allow them to complete their important mission. Others fell into the Siberian ice or suffered from dysentery. One sent to India missed the first transit and spent eight years building an observatory, only to have the sky cloud up on day of the second transit.
How did the astronomers succeed with their earth-to-sun measurements, the purpose of all those difficult and arduous journeys? They came pretty close measuring 93 million miles to 97 million. (93 is what is accepted today.)
If you like science and adventure, you will love these books.
And here’s a link to two safe viewing places tonight to observe this intriguing event: http://www.visitbloomington.com/includes/events/index.cfm?action=displayDetail&menuID=137&eventid=18141 
Here's IU Astronomy's viewing information: http://indianapublicmedia.org/news/iu-astronomy-host-venus-transit-viewing-party-31242/