Challenge #1 – C8, Open Cluster in Cassiopeia
| Target | Type | R. A. | Dec. | Constellation | Magnitude | Size |
| C8 (NGC 559) | Open Cluster | 01h 29m 23s | +63° 18′ 00″ | Cassiopeia | +9.5 | 9.0 arcmins |
Overview
Herschel made the first observation of this relatively faint cluster in November 1787. It’s home to around 120 stars, but only a third of these are brighter than magnitude 12 and readily visible in the eyepiece of a backyard telescope.
Caldwell eight is about 7,200 light-years away from us and 1.8 billion years old.
The statistics around its size and brightness do not seem to promise much, but the view through the telescope, especially on a dark night, is quietly compelling.
Finder Charts
The first sky chart, from SkySafari 6, shows the view looking south at 10 pm in the middle of September. The moon and planets are not shown and stars are only shown to magnitude 5.0.
Cassiopeia is arguably the most distinctive constellation visible at this time of year and, although its obvious ‘W’ shape should readily reveal itself, I’ve marked it with an orange oval, alongside the Big Dipper (Plough) asterism of Ursa Major.
C8 is approximately at the right-angled corner of a triangle where the two bright stars Ruchbah and Segin form the other corners. They are both about 3° away from the cluster.
This third and final finder chart shows stars to magnitude seven. These can help guide you in if your finderscope hasn’t already revealed the cluster’s blurry presence.
From Segin, travel northwards via the fainter stars V987 Cass. and HD 9646. The latter of these two will be in the same 1° eyepiece view as the cluster itself.
This is a tricky find in a smaller telescope, so stay patient.
Now you’ve found this delicate cluster, what should you expect to see?
Individual Telescope Views
The following views will help you find C8 in different telescope types by presenting the images as your telescope will show them. The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Black stars on a white background is often easier to use at the telescope. Each image can be clicked on for a full-screen version. Stars are shown to magnitude 10.0 and the star HD 9546 is the brightest star outside the 1° field of view ring, at the edge of the chart and near the east marker ‘E’.
Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope
Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal
Mirrored View – Refractors and Cassegrain models with a star diagonal show this view
Observation
Smaller telescopes don’t have the resolving power to release lots of stars from the gray fog of the cluster, but larger tubes reward their owners with many more individual suns.
Your starting low magnification will not reveal many stars, but those it does are all around magnitude 12 and appear quite similar to each other and set against a background of the remaining unresolved members of this cluster. As noted above, a smaller scope may mean that you’re relying on averted vision at this stage to see the cluster.
With clusters, more magnification generally reveals more members but often at the expense of the overall view. For C8, nudging magnification higher managed to keep the cluster in the the eyepiece while revealing more individual stellar members. These seem to coordinate into two dominant linear streaks of stars.
PDFs for Printing
Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [C8-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.