TITLE: Symmetries of the Julia sets for $z^2+c$
QUESTION [6 upvotes]: The julia set seems to have symmetries roughly corresponding to translation, rotation and scaling.
In the following image

You can see the horizontal translation, which leaves the extremal left and right endpoints fixed is a symmetry.
The 21-fold rotational symmetry about any one of the 'whorls' is visible also - (I think that the number 21 corresponds to the denominator of the mandelbrot bulb the julia set comes from but I don't yet know how to compute this).
There is also a twofold rotation about the center (and any other part similar to it)
The scales are more difficult to describe and I don't think I have found them all so I will just avoid going into detail on this unless someone would like me to do so.


Do these have a mathematical interpretation, for example as automorphisms of the Julia set in some appropriately understood sense? Or is there some other way to describe these kinds of symmetries in mathematical terms?
Thank you.

REPLY [2 votes]: Yes, there is an explanation, but not in all cases.
Rotational symmetries of polynomial Julia sets are explained in the paper
MR0951972. For the case of rational functions, see also MR1092156.
And also MR1625697 about translational symmetries.
And several papers of Beardon, titled Symmetries of Julia sets.