The Hickson catalog is a collection of 100 galaxy clusters by Paul Hickson in 1982. Hickson compact galaxy clusters are tightly spaced relative to other space objects. A typical Hickson cluster has 4 galaxies, but can have up to 7.
The collection of images below is sortable by their Hickson number, using the top menu option. If you add an image here, please include the tag H and the 3 digit numerical identifier from 1 to 100, such as H=004, in the image description.
Here is an interesting quote about the Hickson catalog from the Sky & Telescope website:
"In 1982, Canadian astronomer Paul Hickson published a list of 100 compact galaxy groups based on his examination of the Palomar Observatory Sky Survey (POSS) red plates. A compact group, as defined by Hickson, is "a small, relatively isolated, system of typically four or five galaxies in close proximity to one another." This sounds like a broad definition, but Hickson used a few more specific criteria to select his groups.
Hickson wanted to compile a uniform sample of groups, so as he made his list, he noted the magnitudes and morphological type of each galaxy in the group. To be included in the final catalog, a group had to consist of four or more galaxies with magnitudes differing by less than 3.0. Each group also had to have a mean surface brightness brighter than 26.0 magnitudes per arcsecond of size. He rejected any grouping where a non-member galaxy not more than 3 magnitudes fainter than the brightest member fell within three radii of the center of the smallest circle possible "drawn" around the entire group. In other words, the groups had to be sufficiently isolated from neighboring galaxies to be included in the catalog."
