Hello All!   
      
   The Mysterious Arc of Venus    
      
   June 4, 2012: When Venus transits the sun on June 5th and 6th, an armada of   
   spacecraft and ground-based telescopes will be on the lookout for something   
   elusive and, until recently, unexpected: The Arc of Venus.    
      
   "I was flabbergasted when I first saw it during the 2004 transit," recalls   
   astronomy professor Jay Pasachoff of Williams College. "A bright, glowing rim   
   appeared around the edge of Venus soon after it began to move into the sun."    
      
   For a brief instant, the planet had turned into a "ring of fire."    
      
   http://www.youtube.com/watch?v=-nXv9YvkNyA   
      
   The Arc of Venus observed during the planet's 2004 transit by amateur   
   astronomer Andr‚ Rondi using a 10-cm refractor near Toulouse, France. [more]    
   Researchers now understand what happened. Backlit by the sun, Venus's   
   atmosphere refracted sunlight passing through layers of air above the planet's   
   cloudtops, creating an arc of light that was visible in backyard telescopes   
   and spacecraft alike.    
      
   It turns out, researchers can learn a lot about Venus by observing the arc.   
   Indeed, it touches on some of the deepest mysteries of the second planet.    
      
      
   The arc of Venus photographed in 2004 by Riccardo Robitschek and Giovanni   
   Maria Caglieris of Milan, Italy. [more] "We do not understand why our sister   
   planet's atmosphere evolved to be so different than Earth's," explains   
   planetary scientist Thomas Widemann of the Observatoire de Paris.    
      
   Earth and Venus are similar distances from the sun, are made of the same basic   
   materials, and are almost perfect twins in terms of size. Yet the two planets   
   are wrapped in stunningly dissimilar blankets of air. Venus's atmosphere is   
   almost 100 times more massive than Earth's and consists mainly of CO2, a   
   greenhouse gas that raises the surface temperature to almost 900øF. Clouds of   
   sulfuric acid tower 14 miles high and whip around the planet as fast as 220   
   mph. A human being transported to this hellish environment would be crushed,   
   suffocate, desiccate, and possibly ignite.    
      
   For the most part, planetary scientists have no idea how Venus turned out this   
   way.    
      
   "Our models and tools cannot fully explain Venus, which means we lack the   
   tools for understanding our own planet," points out Widemann. "Caring about   
   Venus is caring about ourselves."    
      
   One of the biggest mysteries of Venus is super-rotation. The whole atmosphere   
   circles the planet in just four Earth days, much faster than the planet's spin   
   period of 243 days. "The dynamics of super-rotation are still a puzzle despite   
   a wealth of data from landmark missions such as NASA's Pioneer Venus, Russia's   
   Venera and VEGA missions, NASA's Magellan and more recently ESA's Venus   
   Express."    
      
   The arc of Venus as seen by NASA's TRACE spacecraft in 2004. Credit: J.   
   Pasachoff, G. Schneider, L. Golub. From "Venus: It's Now or Never" This is   
   where the Arc of Venus comes in. The brightness of the arc reveals the   
   temperature and density structure of Venus's middle atmosphere, or   
   "mesosphere," where the sunlight is refracted. According to some models, the   
   mesosphere is key to the physics of super-rotation. By analyzing the   
   lightcurve of the arc, researchers can figure out the temperature and density   
   of this critical layer from pole to pole.    
      
   When the arc appeared in 2004, the apparition took astronomers by surprise; as   
   a result, their observations were not optimized to capture and analyze the   
   fast-changing ring of light.    
      
   This time, however, they are ready. Together, Pasachoff and Widemann have   
   organized a worldwide effort to monitor the phenomenon on June 5th, 2012.   
   "We're going to observe the arc using 9 coronagraphs spaced around the world,"   
   says Pasachoff. "Observing sites include Haleakala, Big Bear, and Sacramento   
   Peak. Japan's Hinode spacecraft and NASA's Solar Dynamics Observatory will   
   also be gathering data."    
      
   Pasachoff has some advice for amateur astronomers who wish to observe the arc.   
   "The best times to look are ingress and egress--that is, when the disk of   
   Venus is entering and exiting the sun. Ingress is between 22:09 and 22:27 UT   
   on June 5th; egress occurs between 04:32 and 04:50 UT. Be sure your telescope   
   is safely filtered. Both white light and H-alpha filters might possibly show   
   the arc."    
      
   Enjoy the show!    
      
      
   Author:Dr. Tony Phillips| Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
      
   More Information    
   The 2012 Transit of Venus -- Science@NASA    
      
   The ISS Transit of Venus -- Science@NASA    
      
   James Cook and the Transit of Venus -- Science@NASA    
      
   Live webcast of the 2012 Transit of Venus    
      
   Transit of Venus Images From the ISS -- from the International Space Station   
   (available during and after the Transit)    
      
      
      
   Regards,   
      
   Roger    
   --- timEd/386 1.10.y2k+   
    * Origin: NCS BBS - Houma, LA - (1:3828/7)