The 2012 Transit of Venus

by Klaus Brasch

The transit of the planet Venus across the disk of the Sun on June 6, 2012, was truly a once in a life time event. The previous transit had occurred in 2004, but the next one will not happen until the year 2117. So unless you plan on living well over a century longer, you will not witness an event like it again. Although such occasions may seem of little scientific value in this modern age, that is definitely not the case.

Dr. Paolo Tanga, from the Observatoire de la Cote d’Azur in France, assembled an international team of collaborators from across the world to participate in a very special observational program titled the Venus Twilight Experiment. In a nutshell, the goal of this experiment was to conduct simultaneous observations of the transit from various locations around the globe, using identical, custom made solar coronagraphs, as well as spectroscopic and photometric equipment. By observing Venus as it approached the obscured solar disk, the equipment was designed to visualize and measure light from the Sun’s corona as it was refracted through the atmosphere of Venus. Information obtained this way, could later be applied to transit observations of exoplanet around other stars and help shed light on the composition and physical characteristics of atmospheres of rocky Earth-size exoplanets.

Lowell Observatory was one of 8 locations around the world from which the transit was potentially visible. These locations were selected to both provide multiple observational data and as back-ups in case any of the stations were clouded out. William Sheehan, a long-time collaborator with Tanga, asked CAS members Bill Burke and Klaus Brasch to lend telescope mounts and other equipment and to assist with the experiment at Lowell. This turned out to be a very auspicious combination, since we made an effective team and enjoyed superb observing conditions. As the accompanying photos also illustrate, we also had a great deal of fun doing it.

For more details on the event and some the results see attached PDF: The Venus Twilight Experiment: probing the mesosphere in 2004 and 2012 by Paolo Tanga et al. 2012.

Fig. 1 Paolo Tanga assembling the coronagraphs the day before the transit while Klaus Brasch looks on. (Image by W. Sheehan)
Klaus Brasch and Bill Burke monitoring the transit visually. (Image by W. Sheehan)
Fig. 3 Three of the four Venus transit musketeers, Sheehan, Burke and Tanga (Image by K. Brasch)