Object: NGC 129 Type: Open Cluster

Diameter in '
Number of stars
Brightest star (magnitude)
Distance in parsecs (3.26Ly)
: Cassiopeia
: 00 30.0 / +60.14
: 21
: 6.5
: 193
: 8.7
: 1529
Details sketch
Date / Time
Observing Location
Seeing / Transparency
Magnification / Field of View '
: 07/10/10 / 21:00
: Saint Amand de Coly
: 3 / 4
: Orion Optics UK 350mm
: 22mm Nagler Type 4
: 73 / 68
Observing report
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!

Image from Voyager by CapellaSoft

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).

Image from "Where is M13" by ThinkAstronomy

The six most noticable stars
I checked the stars that I noticed at the eyepiece as rather bright and/or colourful, to see if they belong to NGC 129. In the table to the right you can see some basic data on these stars.

he bright white B9 star, HD2626, does not belong to NGC 129. All the others probably do. Anyway, the table shows I got the colour and luminosity right for all six stars. The bright whit star, HD2626, is a B9 star of magnitude 5.94. The two orange stars, which I thought to be of equal brightness, are indeed two K type stars of almost equal visual magnitude. The three yellow stars that form a triangle in the cluster are all three F-type stars, again of almost equal magnitude. This confirms my visual observation.

One point of discussion is the clusters actual size. In different books and resources, it is stated that NGC 129 is about 21’ in diameter. This could be true if you do not include the bright white star and the fainter stars to the south, and the group to the east including the two orange stars. But that’s always the discussion with open clusters. Which stars do or do not belong to the cluster? This question can only be answered if you know the proper motion of all stars in the field.

If you move the mouse over the sketch of NGC 129 at the top-left of this page, you see the six most noticable stars of NGC 129. The green circle represents the area that most astronomy books and software say is where you find NGC 129.

“SkySafari” by Carinasoft
“Sky Vistas” by Crossen and Rhemann
“Where is M13” by Think Astronomy
Aladin Sky Atlas from CDS
Millenium Star Atlas