Open Cluster NGC 129
The open cluster NGC 129 in Cassiopeia is a relatively young cluster whose age has been estimated to be around 77 million years old and as suggested by the predominance of bluish white stars in the image above. It is believed to be comprised of approximately 35 members stars which are detached from the background sky and without any concentration. Lying at a distance of 5,300 light-years away, the cluster is characterized with a handful of magnitude 8 and 9 stars with the remaining member stars generally being magnitude 10 and 11. NGC 129 lies at the midpoint between β-Cas (Caph, mag 2.26) and γ-Cas (mag 2.17) and is generally visible year-round owing to the fact it is effectively a circumpolar cluster. The cluster’s discovery has been attributed to Herschel (1788) and is currently catalogued in multiple sources.
NGC 129 can be found right in the middle between Beta and Gamma Cassiopeia. This medium sized open cluster lies in a region with many fieldstars, so it is hard to detect the borders of this open cluster. NGC 129 is not really detached from its background, but it is visible with the 35mm Nagler. The 22mm Nagler provides the optimum magnification for NGC 129. In the field of view, just over 1 degree, NGC 129 fits in nicely.
The first impression is overwhelming, an inspiring view. I count more than eighty stars which probably belong to NGC 129. The range of brightness is large, from bright stars to extremely faint members, that can only be seen using averted vision. There are many chains of stars visible, and some dark lanes. The centre of the cluster looks empty somehow. There is no star at the centre of NGC 129.
Just south of the clusters centre I can see a triangle of yellowish stars of almost equal brightness. To the south of the cluster itself, I see a very bright white star. Towards the east I definitely see two bright orange stars, again of almost equal brightness. There is no nebulosity visible of any kind, but with averted vision I see many faint stars popping in and out of view. The drawing of NGC 129 took me 45 to 60 minutes, but it was well worth it. Visually a beautiful open cluster!
NGC 129 lies in an area packed with open clusters. There are in total some 500+ open clusters that you can see on the northern hemisphere, that are above 0 degrees declination. About 100 of these open clusters can be found in an area that runs from the Southeast of Cepheus to the East towards the double cluster in Perseus.
This area is called the Cassiopeia Window, because of the great transparency in this direction of the milky way. It is relatively dust-free. You can look right through our local arm, the Orion Spur, through the inter-arm gap towards the Perseus arm. That is why we can see so many open clusters in Cassiopeia. NGC 129 is situated in the inter-arm gap, at a distance of 5.000 Ly (1529 Parsecs).