Open Cluster Observing List: The Original and Southern Lists

Observe and sketch 100 clusters for Silver, 125 for Gold

• Silver level: observe 100 clusters, sketch 25 of them, and classify all 100 on the Trumpler system.
• Gold level: observe 125, sketch 50, and classify all 125. Only the Gold level earns the pin and counts toward the Master Observer award.
• Imaging: image 100 for Silver or 125 for Gold, and classify them. No sketches are needed.
• Clusters can come from the original list, the southern supplement, or both. Remote telescopes are allowed.

The full Open Cluster list, in the League's order, with a page for each object

Sort any column, or type a name or constellation. The type buttons above the map also filter this table. Best is the month the object is highest at 9 pm. Also on lists the other observing lists the object belongs to, so one observation can count toward more than one program where the League allows it.

69 of the 214 are best in winter: plan the list by month

Each bar counts the objects highest in the sky at 9 pm in that month. An object is also well placed in the month before, late in the evening, and the month after, early in the evening.

62 of the 214 are on another list you may already be working

• Herschel 400: 31 of the 214
• Urban: 22 of the 214
• Deep Sky Binocular: 17 of the 214
• Messier: 14 of the 214
• Binocular Messier: 14 of the 214
• Caldwell: 10 of the 214
• Southern Sky Telescopic: 9 of the 214
• Southern Skies Binocular: 8 of the 214
• Bright Nebula: 6 of the 214
• Herschel II: 1 of the 214

The Trumpler class describes a cluster in three parts

Benjamin Jones chose the original 125 clusters for the League's open cluster guide, published in 2007; a second edition came out in 2025. The southern supplement adds 89 clusters for observers south of the equator. 4 clusters are on both lists.

The Trumpler class has three parts: how concentrated the cluster is (I to IV), how much its stars differ in brightness (1 to 3), and how rich it is (p, m or r for poor, moderate or rich), with n added when it has nebulosity. M11, the Wild Duck Cluster, is I2r.

More Astronomical League observing programs on Go Astronomy

• Herschel II: 400 more of William Herschel's objects, after the Herschel 400
• Binocular Messier: any 50 Messier objects with binoculars
• Urban: 100 objects for light-polluted city skies
• Bright Nebula: emission, reflection and supernova-remnant nebulae of both hemispheres
• Globular Cluster: any 50 of 190 globular clusters, with their concentration class
• Planetary Nebula: 110 planetary nebulae, from the Ring to 16th-magnitude Abell shells
• Deep Sky Binocular: 60 non-Messier objects for binoculars, the step after the Binocular Messier
• Southern Skies Binocular: any 50 of 73 southern objects with binoculars
• Southern Sky Telescopic: 50 of 100 southern objects, most south of -48°
• Messier objects: the Messier Observing Program, the League's first, since 1967
• Caldwell objects: the Caldwell Observing Program
• Herschel 400: the step before Herschel II