"H.Luethen" wrote:

>
>> 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

In about 10,000 years the nodes of Mercury and Venus will coincide
the next time. And, centered on that time, there'll be a "window
in time" some 3000 years long when Mercury and Venus can transit
simultaneously. On the average, there'll be about 0,9 such
double transits for each such "window".


--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/