Challenge #3 – C10, Open Cluster in Cassiopeia
| Target | Type | R. A. | Dec. | Constellation | Magnitude | Size |
| C10 (NGC 663) | Open Cluster | 01h 46m 09s | +61° 14′ 00″ | Cassiopeia | +7.1 | 14.0 arcmin |
Overview
First observed by William Herschel in November 1787. Shining more brightly than its neighbor, M103, this beautiful cluster would be right at home had it been included in the more famous Messier Catalog instead of the Caldwell.
It’s a lovely object for a small backyard telescope to spy, containing around 400 stars, fourteen of which are magnitude ten or brighter – the brightest being 8th magnitude. It is comfortably bright enough to be seen as a feature through a magnifying finderscope.
This cluster is about 6,900 light-years away from us and is about 20 million years old.
Finder Charts
The first sky chart, from SkySafari 6, shows the view looking south at 10 pm in the middle of September.
The large ‘W’ of Cassiopeia is the constellation we’re interested in finding, and it’s strikingly obvious in the northeast sky at this time, and circled in orange in the chart below. For reference, the Big Dipper (Plough) asterism is also circled at the edge of the chart.
This first chart shows stars to magnitude 5.0, and the moon and planets are not shown.
C10, or NGC 663, is located southeast of and between the two bright stars in Cassiopeia, Ruchbah and Segin.
Use the chart below to identify both of these before moving on to the finer detail of the third chart.
Stars are shown to magnitude seven in this final finder chart and you can see the cluster’s green circle inside the blue 1° field of view. To swoop in on the cluster, note the star 44 Cassiopeiae and a faint triangle of stars closer to the main constellation.
Our cluster, C10, is within the same 1° field of view as this small triangle of stars.
In the last section, you’ll discover what you should expect to see of this excellent cluster once it’s in your eyepiece.
Individual Telescope Views
The following views will help you find C10 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. Stars are shown to magnitude 10.0 and the magnitude six star 44 Cass is shown in all charts. The ring is a 1° field of view and you can see two of the triangle of stars within it, and the third star in the triangle is outside the circle, near the [W]est symbol.
Each image can be clicked on for a full-screen version.
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
Your first, low magnification / large field view of this cluster already reveals individual stars, with the brightest shining at magnitude 7.3.
You’ll notice that this cluster appears to be oval in shape, rather than circular, and it’s slanted east to west.
This a beautiful cluster and more magnification to realize several dozen more individual stars should be enjoyed. There seem to be three brighter collections of stars when you do this, caused by a dark lane of dust separating our view of the cluster’s collective heart.
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 [C10-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.