NGC 1746, NGC 1750 & NGC 1758 -- Open Clusters in Taurus
The Confusing Cluster(s)
Tucked away in the corner of Taurus, only 5 degrees from Auriga, is an Open Cluster or a group
of Open Clusters.  From Herschel’s work (around 1785) three NGC numbers were assigned to
this location, a large NGC 1746, and inside the larger cluster, two smaller open clusters NGC
1750 and NGC 1758.  In my older star charts like the Atlas Coel (1962) and Uranometria (1987)
they just show the larger open cluster NGC 1746 with no mention of the two smaller clusters.  
The Intersellarum Deep Sky Atlas (2014) once again lists all three NGC numbers.  

Some clarification as to what is going on is provided in Stephen O’Meara’s book “The Secret
Deep”.  O’Meara lists the two smaller clusters NGC 1750 as his Secret Deep Object 17 and
NGC 1758 as his Secret Deep Object 18. In his book he presents the latest information on this
naming problem.  For details you should refer to his book, but in summary, he concludes from
2003 data that NGC 1750 and NGC 1758 are real but separate open clusters (based on age
of stars) that might, or might not, be in contact with each other, while the designation of the
larger NGC 1746 should be dropped since it appears that the stars outside of the two smaller
clusters do not represent a “true” gravitational cluster.  

Having said that, I have never seen either a hard or electronic star atlas the just marks the
smaller NGC 1750 & NGC 1758 at this location without also including the larger NGC 1746.  
My gut tells me that this issue may not yet be settled.  

In the drawing, I have tried to show where the boundaries of the three clusters are (assuming
all three clusters exist).  The bold outside circle in the drawing marks the edge of the eyepiece,
while the three lighter-circles mark the boundaries of the three clusters – as best as I can
determine. Note -- that the two smaller clusters overlap in the drawing – but one needs to think
in three-dimensions and since the two clusters are at slightly different distances, they may, or
may not, be in actual contact.

Just because the naming is a mess does not take away how pleasing this collection of stars is
in the eyepiece.  If you don’t worry too much about the nomenclature or the gravitational forces
governing these stars and just enjoy the view – it will not disappoint.