However Kepler discovered Tycho had posited intersecting Martian and Solar orbits because he had mistakenly concluded from his data that at opposition Mars was closer to the Earth than the Sun was. The source of the error was a research assistants' mistaken calculation of Mars's daily parallax from observations during its 1582-83 opposition as greater than that of the Sun's presumed 3' parallax.
Kepler discovered that Tycho had mistaken intersecting orbits for Mars and the Sun, attributing it to a research assistant’s erroneous calculation of Mars's daily parallax from observations during its 1582-83 opposition as larger than the Sun's presumed 3' parallax.