C66, Globular Cluster in Hydra
| Target | Type | R. A. | Dec. | Constellation | Magnitude | Size |
| C66 (NGC 5694) | Globular Cluster | 14h 39m 36s | -26° 32′ 20″ | Hydra | +10.1 | 4.3 arcmin |
Overview
The 66th object on Sir Patrick Moore’s Caldwell Catalog list is this enigmatic cluster. Not only is it a long way from us, at around 114,000 light-years, but it’s travelling so fast that scientists believe that it will eventually escape the gravitational clutches of the Milky Way altogether.
To further enhance its enigmatic qualities, C66 is not only one of the oldest clusters we know of – c.12 billion years old – but is so different in composition is so different from other clusters that astronomers believe it may have been born outside of our galaxy.
William Herschel discovered it NGC 5694 May 1784.
This cluster is 140 light-years wide with a mass and intrinsic brightness about 100,000 times that of our sun, although its extreme distance make accurate observations challenging. The brightest individual stars shine at magnitude 16.5, beyond the limits of most backyard telescopes.
Finder Charts
Locate the Sickle asterism in Leo, marked by the orange oval to get a sense of where we are. Also use Arcturus (which can be reached by following the arc of the Big Dipper’s (Plough’s) ‘handle’. From Arcturus, find Spica and Antares. Our galaxy, NGC 5694, is roughly midway between Antares and Spica.
None of the SkySafari 6 finder charts on this page shows the moon and planets. The first chart, below, shows stars to magnitude 5.0 as the sky will look at 10pm in the middle of June.
Note Antares and Spica in the chart below and use it to locate Sigma Librae and Pi Hydrae. These two stars both shine brightly at magnitude 3.3 and our galaxy is almost exactly midway between them.
In this final chart, stars are shown to magnitude 7, and you can see an arc of five stars all of similar brightness (just on the edge of being naked eye-visible in a dark location). The second from bottom of these is 56 Hydrae, shining at magnitude 5.2, which is comfortably visible to the naked eye under a darker sky. Connecting Brachium (Sigma Librae) to it shows the direction to MGC 5694.
For more detail around the galaxy itself, skip to the telescope views, below, which all contain the star 56 Hydrae as a refernce.
Once you’ve got this enigmatic cluster in your eyepiece, what should you expect to see?
Individual Telescope Views
The following views will help you find C66 in different telescope types by presenting the images as your telescope will show them. The first image in each pair 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 ring is a 1.0° field of view. 56 Hydrae is shown in each image.
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
As we’ve already mentioned, this cluster is a long way from us and, accordingly, it is a small sight in the eyepiece. Whatsmore, although not especially clear from the telescope views above, the fianter stars around this cluster form a rich field and make it harder to tease out the cluster at lower magnifications. All that said, playing with averted vision in the right location makes the glow of this distant ball of stars reveal itself.
A little more aperture and magnification breathes more detailed beauty into this little fuzzball of stars. Its bright core gives way to a fainter halo that’s about half its overall diameter.
The brightest stars are still too faint for backyard telescopes, and so there are no individual stars to be resolved in this cluster. Sadly, additional magnification doesn’t help in this regard either.
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 [C66-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.