On 2006-09-11, <Thierry> <Thierry> wrote:
> A question about historical truth.
> It is said that Galileo discovered the phases of Venus phases in 1610. OK.
> It is also said that he invented his scope only in 1610
> Two dates to be confirmed, and if possible in the month close...
> If I simulate the sky at that time, of Firenze, arcetri, we discover that in
> Jan-April 1610 Venus was in the East, 10° over the horizon with 80%+
> illuminated, thus very small, and at the end in the rays of sun. hard to
> imagine that he observed it at that time. It nevertheless could have did it.
> On the other hand, at the autumn 1609 venus shows a fine crescent, and was
> higher in the sky of the morning
> Idem from October 1610 but, this time in the eve.
> However it would have published his Siderius Nuncius in March 1610 (also to
> Impossible thus that he observed the beautiful crescent of venus before
> publishing his book.
> It was thus to have written his explanation and signed the "go for
> printing", say at least 1 month before, in February
> If one assumes that it was very smart, it obviously could have interpreted
> the phases right between the invention of his scope and February 1610.
> But that leaves him just a few weeks, and in counting on clear sky every
> days, to discover the phases and its explanations, under bad seeing, without
> speaking about his optics....
> The book having been published in March, he would thus have observed Venus
> at the worst moment of its phase Or he had to develop his scope in 1609...
> But here also, the first drafts of Giovanni Battista della Porta were
> published in August 1609... (to confirm as well). But that of Galileo would
> not have been invented yet at that time.
> That would tend to confirm that Galileo would have discovered the Venus
> phases at a time it had a small diameter (< 15-12" if I remember well) under
> very difficult conditions (both hardware and astronomical). The discovery
> would all the more be deserving.
> But is this well at that time that all that was held ?
> Who could find me the exact dates (invention of Galileo's scope, 1st obs.,
> obser. of Venus phases, publication of Messenger, etc)
The phases of Venus are in "Dialog Concerning the Two Chief
World Systems", which printed in 1632, and aren't in "Starry
Messenger", which was printed in 1610. There are fairly recent
English translations of both (Stillman & Van Helden).
I've got the Reston bio of Galileo around here somewhere. As
best as I remember, Galileo made a telescope sometime in 1609,
not long after news of the invention reached him.