During the transit, four kinds of contact between Venus and the circular solar edge happen:
External contacts happen at points 1 and 4, internal contacts at points 2 and 3. Presumably, the internal contacts can be observed most easily. We call the corresponding moments contact times. The exact contact times depend on the geographical position of the observers. The difference between the contact times measured at different locations offer the possibility of determining the distance to the Sun.
In this project we propose to observe the exact times of Venus' ingress (contact 1 and contact 2) and egress (contact 3 and contact 4). The goal of this proposal is to repeat the historically important determination of the Astronomical Unit as it has originally been proposed by Edmund Halley (see for instance "Halley's method of durations Its history and appliance").
In additional pages, we
In 2004, similar projects have successfully been organized by the European Southern Observatory ESO and by the German TV-broadcast Quarks&Co. The basic ideas and procedures of the 2004 Quarks project are still available.
For the 2012 transit, other contact time projects are in preparation, for instance that of Steven van Roode. We hope that all of these projects will act in concert procreatively!
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