Hello,
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
re-confirm).
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)
Thanks in avdance
Thierry
http://www.astrosurf.org/lombry