A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Tony Oz
Date: 2018 May 14, 06:03 -0700
No, Kepler first used Mars as a reference point to obtain the figure of the Earth's orbit - and only then (having better precision of Earth's positions) attempted to find the form of the Mars's orbit. Mars has more prominent ellipticity in its orbit than Earth.