"Martin Frey" wrote in message
...
"david" wrote:

Just reading the latest issue of Pop. Astronomy and on page 21, in an
article about the transit of Venus, it states that the event is rar, each
transit ctually occuring in pairs eperated by over a century.

Then it says, and I quote,

"Currently, transits of venuse follow in the order 121.5, 8, 105.5, 8
years
and they will continue in this sequence for another 1000 years".

Now what the heck does that mean?


David

Did you spot that 8+105.5+8=121.5? The pattern isn't quite as odd as
it looks at first sight.


To me it looks like 8 + 105.5 = 113.5.

While the earth goes round 121.5 times, Venus goes round 197.5 times +
4 hours - so it they start together they'll not only be together
again, they'll be at exactly the same point in their orbits 121.5
years later. The 4 hour discrepancy means the pattern of transits
won't last for ever but it'll see us out and another 1000 years.


Actually they will be at the opposite nodes, halfway around their orbits....

My take on this is that the 4 hour discrepancy means that the locations on
Earth that see the next transit in the series, but at the same node, will be
at different longitudes. A bit like solar eclipse saros.

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47