The great Kepler was one of the first to plot the motions of the Earth
along with the orbital motion of Mars using the constellational
backdrop,this diagram is seen on page 86 -

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

The diagram is really a more precise extension of the reasoning of
Copernicus is realising that the backward or apparent retrograde
motion of a planet is really the motion of the faster Earth overtaking
the outer planets in a common heliocentric orbit -

http://antwrp.gsfc.nasa.gov/apod/image/0112/JuSa2000_tezel.gif

Even though modern time lapse footage enables contemporaries to
immediately recognise how Copernicus figured out the Earth has an
orbital motion,it is worthwhile going back to see how Copernicus and
Kepler worked in an era before telescopes ,time lapse footage and the
resources we have at our disposal.

There are many who now look for signs of life on Mars as a means to
generate interest about the planet  but I hope there are at least a
few who still retain the astronomical appreciation of structural
astronomy as it once was practised by putting images in proper
context.The old astronomers would have been amazed at what we have at
our disposal,to learn about our own planet just as much as others,this
approach  may not have the novelty of spacecraft such as Phoenix but
there is something far more satisfying,enjoyable an exciting in the
long run.

On Jul 3, 4:39 pm, oriel36 <kelleher.ger...@gmail.com> wrote:

I assure you that this particular aspect of the reasoning of
Copernicus has not been discarded, amended, or denied by today's
astronomers in the least; the Earth overtaking the outer planets as
the cause of their apparent retrogade motion, and all these planets
together being in orbits which, being heliocentric, have the Sun as
their common center (the faster Earth being in a smaller, inner orbit)
is precisely what continues to be accepted as the true state of the
Solar System.

John Savard