When I first got into astronomy in the mid-1970s, one of the things that grabbed me most significantly was observing night after night in a cornfield at the back of our house, adjacent to our suburban subdivision. I had quite a dark sky outside our little town in southwestern Ohio and could endlessly explore treasures of the night sky, at first with naked eyes and a pair of binoculars. On summer nights, the long arch of the Milky Way, stretching from Cassiopeia in the north through Cygnus and all the way down into Scorpius and Sagittarius in the south, was simply amazing. Filled with glistening stars and pockmarked by myriad rifts of dark nebulae, it was mesmerizing, night after night.

During those first few weeks of my astronomy hobby, I didn't really grasp entirely what I was looking at. And for most of the history of astronomy, no one did. Only in the early 1920s did Edwin Hubble make a breakthrough discovery that led to understanding the true nature of galaxies, which were thought to be “spiral nebulae” and possibly within our own galaxy, for decades beforehand. Aided by discoveries by Lowell Observatory astronomer Vesto M. Slipher (1875–1969), Hubble and others deciphered the cosmic distance scale, at least to a first approximation, and by the mid-1920s astronomers and the informed public understood that we live in a cosmos filled with numerous galaxies and that the Milky Way is just one of them.

Classifying the types of galaxies, however, has been a long and somewhat arduous process. Hubble's original classification scheme, derived following numerous observations and proposed in 1936, consists of a “tuning fork” diagram showing elliptical galaxies on the “handle” branching out into various types of spiral galaxies and barred spiral galaxies on the “tines” of the fork. The galaxies are classified not only by their rough shapes, ellipticals being big spheres of stars, some slightly flattened and some purely spherical, and spirals showing spiral arms, barred spirals being spirals with a prominent bar of material running through their centers, from which the spiral arms originate.