On Oct 12, 2009, at 6:59 AM, Mauro Lacy wrote:
Horace Heffner wrote:
On Oct 12, 2009, at 6:13 AM, Mauro Lacy wrote:
Horace Heffner wrote:
...
...
I really don't think that is possible. There is indeed a slight
apparent retrograde motion of the stars, and it is at an
inclination
to the ecliptic. (The poles of the earth's rotation don't match the
poles of the ecliptic.) It amounts to a yearly revolution. It
occurs
in the reverse order of the signs (astrological solar houses), i.e.
is retrograde. It is merely an aspect of the earth rotating around
the sun in the ecliptic. It is due to the earth midheaven (or nadir
etc.) at any location rotating, with respect to the fixed sky,
roughly an extra 4 minutes every solar day, i.e 24 solar hours.
This
makes the stars seem to be located behind where they were the prior
day, which is an illusion due to the rotation of the earth
around the
sun. The sun is off position (with respect to the fixed stars) 4
minutes a day due to the earth moving forward in its orbit. At
midnight different stars are at the midheaven, and the old stars
appear to move about 1 degree of arc retrograde, i.e. (4 m/(24 h*60
m))*360 degrees = 1 degree. In one siderial day the earth rotates
360 degrees with respect to the fixed stars. In one solar day the
sun rotates 360 degrees with respect to the sun. Since the earth
advances about 1 degree in its orbit, the siderial day is about 4
minutes shorter than the solar day.
Now extrapolate that to a movement of the Sun that is not apparent,
i.e.
that is not caused by the translation of the Earth around the
Sun, but
by the own translation of the Sun, and you'll see what I mean.
The issue is what Galileo meant. What he meant is clear even from
the translation.
I don't know what "own translation of the sun" means. Within the
precision of Galileo's time, the solar system moved as a unit. The
movement of the solar system through the galaxy was not detectible.
The movement of the near stars due to the parallax from the earth's
orbit as baseline was not even known.
And that does not mean that we shouldn't think and consider those
movements today, doesn't it? Even if Copernicus was probably talking
about an apparent movement of the Sun, caused by the Earth's
translation,
Arrrgh! I have had a senior moment here. Sorry! We were talking
about Copernicus and somehow I started referring to Galileo! I
didn't even pick up on the significance of Harry Veeder's remarks!
Everything I said about Galileo applies to Copernicus, not Galileo!
Wow, how confusing and confused is that! I guess I won't be able to
do this stuff much longer. What I meant to say is it is clear what
Copernicus meant in the text you provided.
and even if in Galileo's times the precision does not
allowed them to detect those movements, that does not mean that we are
not entitled today to consider a part of that movement as a real one,
i.e. as a proper movement of the Sun.
Sure, but that is outside the scope of my remarks.
What I'm saying is this: even as early as in Copernicus times, the
door
was open, so to speak, for a consideration of the movements of the Sun
as real(i.e. proper), but somehow in the course of history, that door
was closed or forgotten, and we started to think about the Sun as
fixed,
for all practical purposes.
Yes, but that is not what the quoted remarks mean, which was my main
point.
And we still do this today, for all
practical, cultural, and even scientific and astronomical purposes.
I don't think that is true. It is only true with respect to typical
solar system internal calculations, like trajectories and orbits.
That must and will change in the future; we should start to think
about
the movement of the Sun as a real one, in the same way as we consider
today the movements of the Moon and Earth as proper.
Mauro
I think it is true that astronomers do so when precision requires, as
when predicting future close star locations. What might not be done
is to consider all possible forces involved in such motions, such as
the gravimagnetic Lorentz force due to the gravimagnetic field of the
galaxy, or at least local area of the galaxy.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
