This script creates spirals which match those of Galaxies.
They are not logarithmic spirals.

http://mnras.oxfordjournals.org/content/397/1/164.short

The reference also has an equation for Ring Galaxies, with tanh.
(A quick option to add tanh to the formula did not work.)

The reference also has a formula using angle of pitch.
(Not tried out yet.)

Blend makes a nice curve between the centers of two spirals at 180 degrees.
Also joined edges of a few pairs of spirals and ran planar.
Rebuild can be used.

- Brian




Edit: Correcting typo's. 9/18/2014

Here is the Pitch version, based upon equation 4 of the paper.

The script makes essentially the same curves as the GalaxySpirals script, with one less slider.

"Degenerate" curves going out in various directions, can still occur, and be adjusted away with the whorls slider.

Corrected some typo's in the previous version.

- Brian