> after the recent Venus transit, somebody in our astronomy club had

speculated

> how often we should be able to observe a Venus and Mercury transit at the

same

> time, ie. both planets on the Sun's disk simultaneously.

In the moment it is impossible since Mercury transits occur in May or
November,
while Venus transits occur in June and December. Due to the nodal movement
of
mercury there might be times where the nodal lines of Mercury and Venus
coincide.
That is required for simultaneous Venus and Mercury transits.

But that's not a problem we need to bother with:-)

Hartwig