Collinder - Open Clusters

While many catalogs focus on the tiny and distant, the Collinder Catalogue (Cr) is famous for capturing the "big" objects—star clusters that are often so large or loose they were overlooked by astronomers using high-magnification telescopes.

History & Who Made It

The catalog was created by the Swedish astronomer Per Collinder (1890–1974). It was published in 1931 as an appendix to his doctoral dissertation, On structural properties of open galactic clusters and their spatial distribution.

Collinder wasn't just making a list for fun; he was conducting a massive statistical study of the Milky Way's structure. Most of his work was done using photographic plates from various observatories rather than direct eye-to-telescope observation. Because he was looking at wide-angle photographs, he was able to identify sprawling groups of stars that didn't fit into the narrow view of traditional telescopes.

The Purpose: Mapping the Milky Way

Collinder's primary goal was to understand the spatial distribution of star clusters in our galaxy.

• Cluster Evolution: By cataloging the size and "looseness" of these groups, he helped astronomers understand how clusters eventually drift apart.

• Navigation: Interestingly, Collinder later became a major authority on the history of navigation, but his 1931 catalog remains his most enduring contribution to science.

• Rich Field Observing: For modern amateurs, the Collinder list is the ultimate "binocular" catalog. Many of these objects are too large for telescopes but look stunning in a wide-field view.

What Objects and How Many

The catalog contains exactly 471 objects. While the vast majority are "Open Clusters," Collinder included a few other types of groupings that he felt were structurally significant.

• Open Clusters: 452 (The core of the catalog).

• Globular Clusters: 11 (Actually dense, ancient spheres of stars).

• Asterisms: 6 (Random alignments of stars that aren't actually related).

• Stellar Associations/Moving Groups: 2 (Large groups like the Ursa Major Moving Group).

Collinder Catalogue Showpieces (Flat Text)

Object 1: Collinder 399 (The Coathanger) Constellation: Vulpecula Type: Asterism Note: A perfect "coathanger" shape visible in binoculars. It is not a true cluster, but a chance alignment.

Object 2: Collinder 42 (The Pleiades / M45) Constellation: Taurus Type: Open Cluster Note: The most famous open cluster in the sky.

Object 3: Collinder 50 (The Hyades) Constellation: Taurus Type: Open Cluster Note: The closest open cluster to our solar system, forming the "V" shape of the Bull’s head.

Object 4: Collinder 70 (Orion’s Belt) Constellation: Orion Type: Open Cluster / Association Note: The three bright stars of the belt are actually part of a massive, loose cluster.

Object 5: Collinder 285 (Ursa Major Moving Group) Constellation: Ursa Major Type: Moving Group Note: Most of the stars in the Big Dipper are part of this single group traveling together through space.

Object 6: Collinder 39 (Alpha Persei Cluster) Constellation: Perseus Type: Open Cluster Note: A sprawling group of bright stars surrounding the star Mirfak.

Object 7: Collinder 24 and 25 (The Double Cluster) Constellation: Perseus Type: Two Open Clusters Note: Better known as h and Chi Persei, these are two of the youngest and brightest clusters in the galaxy.

The Observer's Secret: The "Binocular" Catalog

If you try to view a Collinder object with a high-power telescope, you might see nothing but random stars. The "secret" to the Collinder catalog is low power. These objects were discovered on wide photographic plates, and they are best enjoyed through binoculars or "rich-field" telescopes that provide a wide window into the sky.

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