Pat Flannery wrote:
Alain Fournier wrote:

It would be possible to do so. But you would have to build
something really huge or assume that the receiving end has
telescopes and know where to look. If you know that there
is someone listening at the other end you could go that way.
But I never heard about any Earthling trying to signal the
inhabitants of the moon that way.



There were plans to contact other planets via earth-based signs and
signals proposed in the past; there is an article about some of the
ideas he
http://seti.org/seti/our_projects/in.../messages.html

Interesting article. But those were just plans. Never
implemented because as I said you need something really
huge.

One difference would be that moving clouds would be visible on the other
planet, and it wouldn't take much imagination to realize what they were.

Yes clouds would help the imagination. But I think that many
people in a period of a few millennia before 1800 knew that
the moon was a place where one could walk but didn't know that
the moon didn't have an atmosphere. Many of those people probably
thought that there might be people living on the moon. They didn't
try to communicate with the moonlings because it was too difficult.

And the lights of major cities would also be visible through even
primitive telescopes if it possessed a technological civilization that
built cities.

Once you have major cities with serious lighting, communication
becomes much easier. Here on Earth the time between the first
electrified major cities and the famous stroll of Neil Armstrong
was just a few decades. If those few decades happen at the same
time on both of the twin worlds then yes very interesting things
can happen. But I think that it is extremely unlikely that the
two worlds would evolve at the same rate for a few billion years
and be both at the same evolutionary stage to a precision of
a few decades. Nonetheless, even if it is very unlikely it is
fun to imagine what would happen in such an interesting case.
Maybe we will live to see something similar. Imagine if SETI
makes contact with a world at about our evolutionary stage.
Not very likely, but it would be very interesting.

Of course finding a world with life at a different evolutionary
stage would be also be interesting. But in such a case information
flow would essentially be one way. I think that would make it
less thrilling.

Alain Fournier