What the term 'Periodic times' means

For those who like intricate reasoning,they can enjoy Kepler's
argument for replacing the Sun's position between Mars and Venus with
the Earth's orbital motion.




Epitome Of Copernican Astronomy by Johannes Kepler


Finally by what arguments do you prove that the centre of the Sun
which
is at the midpoint of the planetary spheres and bears their whole
system - does not revolve in some annual movement,as Brahe wishes,but
in accordance with Copernicus sticks immobile in one place,while the
centre of the Earth revolves in an annual movement.


Argument 10


" The 10th argument,taken from the periodic times, is as follows; the
apparent movement of the Sun has 365 days which is the mean measure
between Venus' period of 225 days and Mars' period of 687
days.Therefore does not the nature of things shout out loud that the
circuits in which those 365 days are taken up has a mean position
between the circuits of Mars and Venus around the Sun and thus this
is
not the circuit of the Sun around the Earth -for none of the primary
planets has its orbit arranged around the Earth,as Brahe admits,but
the
circuit of the Earth around the resting Sun,just as the other
planets,namely Mars and Venus,complete their own periods by running
around the Sun." Johannes Kepler