Challenge #4 – C58, Open Cluster in Canis Major
| Target | Type | R. A. | Dec. | Constellation | Magnitude | Size |
| C58 (NGC 2360) | Open Cluster | 07h 17m 43s | -15° 38′ 00″ | Canis Major | +7.2 | 13.0 arcmin |
Overview
Caroline Herschel discovered this cluster in February 1783. Its combined magnitude of 7.2 puts its hundred stars beyond naked eye reach, but they can be comfortably gathered in by binoculars. None of the individual stars shines brighter than magnitude 10.5.
The cluster is around 3,700 light-years away from us, is 15 light-years across, and about 2.2 billion years old.
Finder Charts
Orion will help us find this open cluster, and it’s circled orange in the first star chart below. In it, we’re looking southeast in the middle of January at 10pm. Stars are shown to magnitude five and the moon and planets are not shown.
See how the belt stars of Orion point to Sirius, the brightest star in the night sky.
Sirius is the brightest star in Canis Major and either side of it we see the stars Murzim and Muliphein. It is the second of these, proerly known as Gamma Cani Majoris, that we need to focus on to get to C58.
To the east of Muliphein, we’ll find a collection of stars on the edge of naked-eye visibility but that are easily seen in binoculars or a magnifying finderscope. The blue circle is a 1.5° field of view and inside it we have HR 2758, HD 56310, and R Canis Majoris.
Our open cluster, C58, is inside the same field of view that contains these three stars and is closest to the magnitude 5.4 star HR 2758.
In the last section, you’ll discover what you can see of this little cluster.
Individual Telescope Views
The following views will help you find C58 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. The large circle is a 1.5° field of view and the three stars identified above are all shown within it.
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
This pretty cluster can be viewed as the regulation ‘hazy patch’ with binoculars, but a small telescope breathes life into 40 or 50 individual stars. They are tightly clustered and present a dramatic scene of the tiniest pinpricks of light, all appearing roughly similar around magnitudes 10-12.
Patterns inevitably form in the mind’s eye when we see so many dots so close together. How do you view these whorls and loops of stars? Overriding these lines of distant suns, observe the density of them towards the core of this cluster and how it seems to be the source of so many of the patterns we just mentioned.
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 [C58-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.