Object: NGC 2420 (Collinder 154)

Constellation
RA / DEC
Diameter in '
Magnitude
Number of stars
Brightest star (magnitude)
Distance in parsecs (3.26Ly)
: Gemini
: 07 38.4 / +21 34
: 6
: 8.3
: 304
: 11
: 1944
Details sketch
Date / Time
Observing Location
Seeing / Transparency
Telescope
Eye-piece
Magnification / Field of View '
: 27/12/08 / 00:34
: Landgraaf
: 3 / 5
: Orion Optics UK 300mm
: 12mm Nagler Type 4
: 133 / 37
Stacks Image 2216
Observing report
With the 300mm Dobson and the 35mm Panoptic I see NGC 2420 as a smudge, so it's not an easy object, but on the other hand it isn't too difficult. Giving the tube a little nudge, makes the smudge stand out more clearly from the dark background. Increasing the magnification with the 12mm Nagler T4 to 133x, helps to resolve this small and compact cluster partially. With the 7mm Pentax it's resolved even more, but I like the view in the 12mm better, so that will be my optimum magnification for producing the sketch.

With direct vision I count about 20 stars, a relatively poor cluster. However with averted vision the number of stars increases rapidly, and becomes about 40 to 50 stars, so this would make it a moderately rich cluster. According to Hynes (Star clusters) there are about 300 stars in this cluster, but visually I don't see more than 50, whatever I try. There are no dark lanes visible and there is no central star or a star with a specific colour in NGC 2420. I do not detect any significant double or multiple stars.

To the south of the cluster, is a bright yellow-orange star visible. I don't know if it belongs to the cluster but I will put it in the sketch anyway. With averted vision I not only see more stars popping in and out of the field of view, but I also notice a glow of unresolved stars. I do not see any asterisms in the cluster, except for a group of 4 stars on the southern edge of the cluster that seem to form a kind if hook. NGC 2420 looks a little irregular with no real centre.
Notes
Stacks Image 2230


NGC 2420 can be found about 2 degrees northeast of the Eskimo Nebula (NGC 2392). William Herschel discovered this cluster on November 19th 1783, while doing one of his sweeps with his 18.7-inch reflector (Steinicke, Historic NGC). To the left you see the log of the observation by the Herschels on November 19th, 1783:
"Cluster of stars very beautiful and close; of a considerable extent, perhaps 6 or 8' ; 2 degrees Sw following .. (63) Geminorum; ...(48) mvp; I counted 50 or more .. suspect perhaps double that number".

(Source: The Herschel Archives)

Stacks Image 2241


Distance and size of NGC 2420

NGC 2420 lies within the Perseus arm (see image below), at a distance of almost 7.000 light-years. If NGC 2420 would be at the same distance as the Pleiades, which is 440 light-years, its visual magnitude would be 2.3 and its angular size would be 1.5 degrees or three full moons.

(Source: "Where is M13 by Bill Tschumy, www.thinkastronomy.com)

SAO 79563

The bright yellow orange star to the south of the cluster is SAO 79563, a magnitude 9.11 star of the type G0, with a temperature of 4800K (Source: Voyager from Carinasoft). As I suspected, it does not belong to the open cluster NGC 2420.

Stacks Image 2251

(Source: Voyager by Carinasoft)