I'm hanging out for this one.......
http://www.fourmilab.ch/documents/ca.../a26982532.gif
there is, or rather will be, a simultaneous transit of Mercury and Venus visible from the Earth. It will happen in the year 69163, on the 26th of July (assuming the calendar hasn't been changed to re-synchronise trivialities like the Earth's rotation and orbit with grander matters such as the planets in their orbits, which is not the way to bet--astronomers will prefer to identify this as the event of Julian day 26982533 [barycentric dynamical time].)
ohps found info here....
http://www.fourmilab.ch/documents/canon_transits/