NGC 188 – A Very Faint and Difficult Open Cluster, and so Close to Polaris

Image by James Dire:  Observer from Illinois 

Telescope:  5.2-inch f/7 apochromatic refractor, 25 minute exposure with an SBIG ST-2000XCM CCD camera.  Date of image:  April 26th 2020 

NGC188

 

Visual Notes by Sue French:  Observer from New York 

I’ve logged NGC 188 only twice:  By Sue French 

7-10-02, 10:25pm EDT, 105/610mm refractor, 87×, Seeing: fair, 

Transparency: good

About 30 faint to extremely faint stars in 17′. Slightly patchy background hits at unresolved stars. Inconspicuous.

 5-25-06, 2am EDT, 10-inch f/5.9 Newtonian, 68×, Seeing: poor, 

Transparency: fair

In a pretty field of bright stars.  Large, about 14′.  Nice cluster.  About 40 faint to very faint stars over patchy haze.

You’ll notice that my estimated size is different between the two observations.  Brent Archinal gives this a size of 15′.   

 

Visual Notes by Uwe Glahn:  Observer from Germany 

 4-inch binocular:  Magnification 23x, NELM 6.0 

     Stands out nicely from the background, visible with direct vision, large diffuse glow without any concentration, half-dozen stars are popping in and out of view within the cluster. 

 16-inch  NELM 6.5+

     Nearly fully resolved, very many (>50) faint mag. 14 stars with similar brightness, OC without any concentration or structures, some background glow.  

Pencil sketch:  20 x 125 binoculars and a 3º field of view. 

NGC188_ug

 

Rony De Laet:  Observer from Belgium 

The existence of this cluster was brought to my attention, back in 2005, when I became interested in sketching the Caldwell Objects. 

NGC 188 is the first entry in the Caldwell list, which is a list that orders objects from highest declination to lowest. Much to my surprise NGC 188 was located near Polaris, a convenient location to observe from my backyard. At that time, I had a computer controlled 105mm f/14 Maksutov-Cassegrain telescope. 

I was pretty sure that my scope was pointed in the right direction, but when I looked into my 25mm EP…nothing but an empty field.  This was weird.  The cluster’s magnitude was rated at 8! That should have been a piece of cake, as I’d  sketched dimmer objects like M56. 

I read James O’Meara’s notes on Caldwell 1 a few hours earlier.  He even mentioned seeing the cluster with a small pair of binoculars.  Just to be sure, I sketched the stars in the field of view, but I wanted to know what went wrong. 

I believe there are two reasons why NGC 188 was beyond my reach. 

The first reason:  The majority of the stars are below the limiting magnitude of my telescope.  From my backyard, I could not see stars fainter than mag 12.5 with my 4-inch Maksutov-Cassegrain.  

The second reason is that NGC 188 is relatively large, so its combined brightness is spread over a large area, compared to a globular cluster like M56.  I had bad luck, that this cluster’s combined brightness was lower than the sky’s background brightness. 

Here are my notes and sketch from then.

Telescope:  4-inch Maksutov-Cassegrain 

Location : Bekkevoort, Belgium

Date:  November 1, 2005 , 20.45UT

Seeing:  2.5 on a scale of 5, Transparency : 3.5

Magnification: 60x

Fov 0.9°

I made the following sketch on a very dark (for my standards) night.  It was not much of a cluster to me in the ETX.  Only the brighter members are visible. The limiting magnitude is 12.5, so I guess this object is just beyond my reach.  

North is down and west is to the left: 

80klaar

 

From the early years of the Observer’s Challenge Report: AUGUST 2010 OBSERVERS CHALLENGE – NGC-188 

 

Explore posts in the same categories: Work File Only - Observer's Challenge Reports

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