On Thursday, January 24, 2019 at 5:09:00 PM UTC-7, Mike Collins wrote:

So you’ve finally realised. You have given a link to a site which
demonstrates perfectly that from the point of view of the Sun there are no
retrogrades.

I don't think he _ever_ had an issue with that fact. Although, given the number
of real astronomical facts with which he does have issues, I understand that it
may be somewhat confusing to sort out one from another.

He recognizes the achievement of Copernicus in showing the planets don't orbit
the Earth, they orbit the Sun. He praises and applauds Copernicus, Galileo, and
Kepler.

And he has also affirmed that the retrograde motions of the outer planets are
illusory, rather than real; an artifact caused by the Earth's motion around the
Sun.

An issue that has recently come up is that he has stated that the retrograde
motions of Mercury and Venus *are not illusory*. Some people here have taken
issue with that statement. After all, if there are no retrograde motions from
the true viewpoint, the view from the Sun, how can any retrogrades we see be
anything but illusions?

But allowing for the fact that as he has an unusual perspective on the Solar
System and its motions, and so he doesn't use the same language as the rest of
us, it seems to me that what he is stating is a correct and true fact about the
Solar System, even if it isn't the novel original discovery on his part that he
thinks it is.

Look at the moons of Jupiter. They move backwards as well as forwards in their
orbit of Jupiter from our point of view. Is that an illusion?

No; the motion we're seeing is their real orbital motion around Jupiter.
Sometimes it's direct, and sometimes it's retrograde, because we're seeing the
system *from the outside*.

Similarly, when we see Venus and Mercury in retrograde motion, that retrograde
motion *is their real orbital motion around the Sun*. It isn't the Earth's
motion around the Sun that makes them look like they're in retrograde motion -
it's the fact that the Earth is farther away from the Sun, so when they pass in
front of the Sun, the direction of their orbital motion is reversed *because
we're seeing it from outside the orbit*.

The Earth's motion around the Sun makes an illusory contribution to their
motions of a progression through the Zodiac in the direct direction once a year,
moved along by the apparent motion of the Sun through the Zodiac.

If one looks at a drawing of the apparent orbits of the planets from Earth's
point of view, one sees a series of loops going around the Earth. The loops are
made by a big circle, giving the overall motion, and a little circle, adding the
loopy curlicues.

For an outer planet, the big circle has the period of the planet's orbit around
the Sun, and the little circle the period of the Earth's orbit around the Sun.

For an inner planet, the big circle has the period of one year - and the little
circle has the period of the planet's orbit around the Sun.

So the loops in the apparent orbit are "illusions" caused by the Earth's motion,
and not part of the planet's real solar orbit - for an outer planet.

For an inner planet, the loops are the planet's real solar orbit - as we see it
from outside - and the apparent overall orbit is the contribution of the Sun's
illusory apparent motion around the Earth.

He noticed this, and is calling attention to the fact that for the inner
planets, the retrogrades aren't illusions imposed by the Earth's motion, but
instead are to be expected from observing the reality of those planets' always-
direct motion around the Sun from the *outside* _position_ of the Earth.

That he has managed, for once, to actually get something _right_, however
clumsily he may express this insight...

causes me to be dismayed when those who, knowing astronomy properly, without the
confusion from which he suffers, mistakenly tell him he is wrong once agaoin.