oriel36 wrote:

You are learning from an astronomer rather than getting your
information about Kepler and his discoveries via the empirical cult
and specifically Newton's awful use of Keplerian
insights.Technically,if you wish to discover where Newton jumped the
tracks you listen intently to what Kepler has to say,then you look at
the technical mistake of Newton.

Hi, there, and I'd certainly regard it as common knowledge which I
learned as a child that Kepler based his formulations on the
observations of Tycho Brahe, sometimes regarded as one the last
outstanding astronomers of the pre-telescopic period.

Before getting to the diagram, which I'm still digesting (reading
the whole article, which I just downloaded will help), I should make
an important point about how astronomers can and do view
"magnification" in perspective, and without discounting the value
of naked eye observation.

Thus in 1612, Simon Marius viewed the Great Nebula in Andromeda
(now known as the Andromeda Galaxy, or M31, or NGC 224) with an
early telescope and soon published a description, saying that
its luminosity had a quality like light viewed through transparent
horn. (An interesting image -- I wonder what kind of horn.) His
discovery was cited as the first in a number of other publications
over the next 150 years or so at least in Europe.

However, in fact, Abd-al-Rahman al-Sufi in Persia had observed and
described this same "little cloud" and published his observation
in 964 -- so that Marius merely independently rediscovered with
the novel optical aid of the telescope what al-Sufi and others
had seen with the naked eye.

Thus while telescopes are a big topic on sci.astro.amateur, this
shouldn't mean that naked eye observing is discounted -- nor
reasoning, which for example in the 14th century led Nicholas
Oresme to suggest that it would be more elegant to posit a
diurnal rotation of the Earth than a revolution in the same
period of the whole cosmos, some two centuries before the
telescope came into astronomical use.

Do you clearly understand what is goin on in the diagram on page 86 -

http://mitpress.mit.edu/journals/pdf/POSC_13_1_74_0.pdf

It's a striking diagram, with the retrograde motions or whatever aptly
called "pretzel"-like in a caption.

Let me help you along -

"Copernicus, by attributing a single annual motion to the earth,
entirely rids the planets of these extremely intricate coils [spiris],
leading the individual planets into their respective orbits
[orbitas],quite bare and very nearly circular. In the period of time
shown in the diagram, Mars traverses one and the same orbit as many
times as the 'garlands' [corollas] you see looped towards the
centre,with one extra, making nine times, while at the same time the
Earth repeats its circle sixteen times " Astronomia Nova 1609 Kepler

Do you clearly and I mean clearly understand how retrogrades are
resolved using orbital comparisons and from there to the Keplerian
orbital refinement such as a less than circular orbit.

For clear understanding at this level, I'll need to study the whole
article carefully, which should be much worthwhile -- and I'll thank
you warmly for directing me to this source.

I'm not sure if I'd call an ellipse a "less than circular" orbit, only
a member of the set of elliptical orbits of which a circular one would
be a subset. All I know is that by introducing the hypothesis of the
ellipse, he simplified lots of complications that would arise with
circular orbits, geocentric or heliocentric.

Do you clearly understand what is badly wrong with Newton's worthless
view of and resolution of retrogrades based on his misintepretation
of that diagram of page 86 -

" For to the earth planetary motions appear sometimes direct,
sometimes stationary, nay, and sometimes retrograde But from the sun
they are always seen direct ," Newton

I'm not sure, it sounds to me like he's proposing the Sun as a good
frame of reference, since according to Kepler, if I recall correctly,
the sun is a focus of a planet's elliptical orbit.

Poor Isaac,thought if you replaced the Earth with the Sun at the
center of the diagram that retrogrades disappear or rather the poor
fools who followed Isaac in this careless belief.Perhaps there is a
severe reading disability in that you cannot read what Kepler is
saying -

"Mars traverses one and the same orbit as many times as the
'garlands' [corollas] you see looped towards the centre,with one
extra, making nine times, while at the same time the Earth repeats its
circle sixteen times " Astronomia Nova 1609 Kepler

Maybe this is a crude amateur astronomer's misunderstanding, but I'd
take Newton as saying that from the Sun's perspective or frame of
reference, the planets are revolving in their orbits in consistent
directions -- although from Earth's perspective, for example, another
planet may appear to "change course" in retrograde motion, which, of
course, was a reason for all of those epicycles of the Ptolemaic
model, which an elliptical and heliocentric model can nicely make
unnecessary.

Let me guess,you never seen the Panis Quadragesimalis of Kepler
before,a representation which plots the motion of Mars against the
stellar background and then compares those plotted positions for Mars
with the orbital cycles of the Earth.Of course,you are an astrologer
and paste planetary motion to celestial sphere geometry via the Ra/Dec
system so Newton could justify the old calendrically based
'predictive' system for planetary location.

Please let me distinguish between some of the questions and assumptions
you present here. It seems to me that some of this discussion is about
the most useful frame of reference to use for certain purpose, and part
about the definition of an "astronomer" or "astrologer."

Thank you for presenting your ideas in a friendly dialogue, and I'll try
to do the same. Obviously the more I learn about Solar System dynamics,
the better an astronomer I'll be. And if the dialogue helps us both to
formulate better our concepts of "astronomy" or "astrology," then we
may both benefit.

I understand judicial astrology as the study of the stars and planets
for the purpose of assessing a person's character based largely on the
configuration of the heavens at the time of the person's birth, or of
assessing the "aspects" of that person's situation (or possibly of
some collectivity such as a given organization or nation or even the
general terrestrial scene) based on the configuration obtaining at
a given point or time, or over a given period of time.

I understand astronomy to be a branch of natural philosophy or
science concerned with what William Herschel has well called "the
construction of the heavens," to be ascertained both through
observation and through the application of reason.

When I use RA/Dec, I am well aware that this is merely a mathematical
model of convenience, and that in reality the universe is not a
geocentric sphere. If a telescope were located on the Moon, I might
use a lunar version of RA/Dec -- aware that that, too, would be
merely a useful model.

Pragmatically, I'd say that if people formulate useful laws of
motion like Newton that serve as a basis of celestial mechanics;
or discover and catalogue thousands of nebulae (as we now understand,
nebulae, open and globular star clusters, and galaxies) like Caroline,
William, and John Herschel; or study Cepheid variables and discover
the period-luminosity relationship like Henrietta Swan Leavitt, then
they are doing astronomy.

Consider, for example, the evolution of standard candles and yardsticks
for judging cosmic distances, ranging from parallaxes of nearby stars
to gravitational lenses and the like for the most distant galaxies.
However we view Solar System motions or timekeeping -- and I suspect
that everyone agrees on Keplerian mechanics and the length of the
sidereal days, however apt or otherwise you or I may consider
specific expositions of these -- astronomy is about the larger
universe, also, as your recognize in making some of your queries
about galactic revolution, for example.

What I'm seeking to do is not to cast horoscopes, but humbly to
follow in the footsteps of such as these -- with the awareness,
of course, that I'm unlikely with a 20cm Newtonian reflector to
make any new discoveries when it comes star clusters, nebulae,
or galaxies, my main interest; and also that I'll learn most
by taking my visual observations as opportunities to learn about
observations made using other electromagnetic wavelengths also.

In sum, I very much follow Nicholas of Cusa, Galileo, Newton,
and Einstein in recognizing that choices of frames of reference
are arbitrary -- with RA/Dec merely one convenient convention
for certain purposes.

Again, I appreciate your courteous invitation to dialogue, and
hope that I can worthily reciprocate.

Most appreciatively,

Margo Schulter

Lat. 38.566 Long. -121.430