Collinder 89 -- Open Cluster in Gemini
The 9-12 Geminorum Cluster
I was leafing through my newly arrived Sky & Telescope Magazine (February 2021) when
Mathew Wedel’s Binocular Highlights – In the Twins’ Toes caught my attention.  The large
loose Open Cluster Collinder 89 did not register with me.  A quick review of my observing
notes and drawings made me realize that Collinder 89, although an obvious binocular
object, had missed my attention all these years.

Collinder 89 is large, covering about a degree of sky.  Its 15 or so stars are loosely arranged
and dominated by the stars 9 Geminorum, 10 Geminorum, 11 Geminorum and 12
Geminorum.  These four stars showed easily in my 7 x 42 binoculars from the deck of my

Using the 155mm refractor, I took a closer look at the cluster.  The star field was quite
pleasing to the eye.  The double asterism of four bright stars forming a Y-shape and two
isolated bright stars dominated the view.  

Technically, the stars 8 Geminorum and HD 43966 are just outside of Collinder 89 but
adding these two stars of near-equal magnitude to the other four (true cluster members)
made for a more esthetic and logical star pattern in the eyepiece (at least to me).  A little
searching in the literature revealed that this cluster also goes by the name of the 9-12
Geminorum Cluster.