A counter-winding spiral galaxy has two usually non-overlapping sets of
spiral arms that open outward in opposite directions. The first example,
NGC 4622, was discovered by Dr. Gene Byrd. At right is the weblink
for our major paper on the structure of this galaxy that shows
how we came to the conclusion that the two strong outer arms are leading.
Another example recently studied is ESO 297-27, also linked at right.
In this case, studied by my former student Dr. Rebecca D. Grouchy,
we determined that an inner single spiral arm is leading.
NGC 4622 as observed in visual light with the Hubble Space
"The Ringed Spiral Galaxy NGC 4622. I. Photometry, Kinematics, and the Case for Two Strong Leading
Outer Spiral Arms," by Ronald J. Buta, Gene G. Byrd, and Tarsh Freeman, Astronomical Journal,
125, 634, 2003
Counter-Winding Spiral Structure in ESO 297-27, by R. D. Grouchy, R. Buta,
H. Salo, E. Laurikainen, and T. Speltincx, Astronomical Journal, Vol. 136, p. 980