Challenge #3 – C64, Open Cluster in Canis Major
| Target | Type | R. A. | Dec. | Constellation | Magnitude | Size |
| C64 (NGC 2362) | Open Cluster | 07h 18m 41s | -24° 57′ 00″ | Canis Major | +3.8 | 5.0 arcmin |
Overview
Giovanni Battista Hodierna discovered this bright cluster prior to 1654, when he published details of it. In modern times, we didn’t discover this record until the 1980s, and so believed that William Herschel was the original finder of it in March 1785.
This is a bright collection of around 150 stars in a very small patch of sky making it one of the best sights available to smaller scopes from the Caldwell catalog.
The cluster is about eight light-years wide but is over 1,500 light-years away from us. At that distance, our own sun would only shine at magnitude 15.5, giving you a sense of how bright Tau CMA is, the brightest star in the cluster. This is one of the most luminous supergiant stars we know of and is about 50,000 times brighter than the sun.
By astronomical standards, the cluster is a youngster at just 5 million years old.
Finder Charts
The first sky chart, from SkySafari 6, shows the view looking south at 10 pm in the middle of March, looking south.
We’re looking for Canis Major, which is an easy constellation to find because it’s home to Sirius, the night sky’s brightest star. For ease of orientation, I’ve also highlighted Orion and the Sickle asterism in Leo.
This first chart shows stars to magnitude 5.0, and the moon and planets are not shown.
Find the stars Wezen and Adhara, Delta and Epsilon Canis Majoris, respectively. A line imagined from Adhara to Wezen and carried on for roughly the same distance ends at C64 (NGC 2362).
Stars are shown to magnitude seven in this final finder chart which reveals much more of the detail. Note the star i29 Canis Majoris near the cluster and the bright dot of Tau Canis Majoris shining at the heart of the cluster.
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 C64 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 with 27 and 29 Canis Majoris labelled.
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
Pointing your telescope at Tau Canis Majoris reveals a stunning view of twenty or more tiny pinpricks of light nestled around it.
With higher magnification, you’ll be able to boost that count to fifty or more in a very small area of sky.
I think you’ll agree that this is a dazzling sight!
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 [C64-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.