Monday, May 28, 2012

Awaiting Venus

The countdown has begun as the world prepares to see Venus make its transit across the Sun, a rare event and the last of its kind this century. On June 5-6, 2012 we should be able to watch Venus appear as a black spot and glide slowly across the face of the Sun. Some quick facts about the Transits of Venus: 
  • They occur at gaps of 8,121.5, 8, and 105.5 years (the full pattern repeats every 243 years).
  • The last one occurred in 2004. After 2012, the next one is not due until 2117! 
  • Depending on where you are (see map below), you may be able to watch the full transit, only the entry (before sunset), only the exit (after sunrise), or neither. 

Transit of Venus, 2012
Map showing world visibility of the Transit of Venus, 2012

The rareness of this event alone (remember we won't be alive to watch the next one) makes it a spectacle worth waiting for. But there is more to the story. The Transit of Venus, as it turns out, had a critical role in shaping modern day science. To see how, we must travel some 300ish years back in time: 
"In 1716 British astronomer Edmond Halley published a ten-page essay which called upon scientists to unite in a project spanning the entire globe  one that would change the world of science forever. On 6 June 1761, Halley predicted, Venus would traverse the face of the sun  for a few hours the bright star would appear as a perfectly black circle. He believed that measuring the time and duration of this rare celestial encounter would provide the data that astronomers needed in order to calculate the distance between the earth and the sun ... Halley was sixty years old when he wrote his essay and knew that he would not be alive to see the transit (unless he reached the age of 104), but wanted to ensure that the next generation would be fully prepared."
The quote is from Andrea Wulf's Chasing Venus: The Race to Measure the Heavenswhich I read as a part of the monthly Book Club for the Curious organized by the Museum of Science, Boston. This book narrates the story of the dauntless 18th century astronomers who battled all odds to answer Halley's call. For the data to be of any use, the transit duration had to be measured from two locations as distant as possible in the two hemispheres. This was an age when clocks were imprecise, transportation was challenging (communication more so), a large part of the globe was still uncharted, there was no reliable way to measure the longitude, and the political climes in Europe were tense and volatile due to the Seven Years' War and competition between colonial nations. Yet a number of expeditions were launched to view the transits in 1761 and 1769. To name a few, Le Gentil set sail toward Pondicherry on both occasions, Chappe traveled to cold and dreary Siberia in 1761 and to Baja California in 1769, and Green joined Captain Cook on his voyage to Tahiti and beyond on the Endeavour in 1769. Some of the struggles ended in deep disappointment. Some astronomers could not make it to their destinations on time. Even among those who did, data collection would be jeopardized by clouds and inclement weather and by the black drop effect. In spite of all the odds, the observations from 1769 yielded an estimate of 93,726,900 miles for the astronomical unit (only 0.86% off from today's estimate of 92,960,000 miles). What made the efforts particularly significant though was the fact that they promoted global scientific collaboration on a scale that was unprecedented. This collaborative spirit is so deeply ingrained in the modern scientific culture that we have learned to take it for granted. It was also the first time governments worldwide funded large scale scientific projects, a trend that has trickled down since.
Coming back to 2012, I can't help but marvel at where technology has brought us today. While digging through the internet resources on this topic, I stumbled upon a free smartphone app that allows individuals to contribute transit timings from different locations worldwide. It is a collective initiative that seeks to measure the astronomical unit following Halley's method. A feat that 250 years back would require several tons of hefty quadrants and pendulum clocks, long voyages through perilous uncharted waters, and, above all, bottomless grit can now be achieved by a tap on a touchscreen! 
The upcoming transit will of course help further science. It will aid modern day astronomers on their quest for exoplanets (planets encircling stars other than the Sun). Exoplanets are usually detected from the dip in the intensity of a star's brightness. Venus (now a well-studied model planet) viewed from the Hubble, Venus Express, and terrestrial observatories will help refine our methods for estimating characteristics (e.g. size or atmospheric composition) of distant and less familiar exoplanets. 
If you are wondering where you can view this spectacle, this NASA link may help locate your closest observatory open for public viewing. If, for some reason, you cannot access a telescope, you can always tune in to NASA's live webcast from the summit of Mauna Kea, Hawaii. And, before you set out to enjoy this once-in-a-lifetime event, don't forget to pre-order a pair of eclipse glasses!

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