Globular Star Clusters

Globular cluster are amongst my favourite deep sky objects to observe with my 16" Newtonian. A telescope in this size range allows you to see the true colour of many objects. Whereas the relatively young open clusters have white and bluish stars with the occasional red star, globular clusters, which are dominated by old stars, have a golden colour. Best to avoid red dot finders and red flash lights if you want to see the colour in the eyepiece. Globular cluster divide into two groups: ω Centauri and everything else. This is the largest globular cluster in our galaxy by far. In the following images I have presented all clusters in a frame that is 14' across, about half the angular diameter of the Moon. So you can see the relative sizes if you decide to observe them. The larger clusters including ω Centauri, NGC104 and M22 are also framed in a wider field. I have also processed the image to capture the colour as best as possible as seen visually through a 16". And I have taken care not to burn out the central regions. The range of star concentration is surprizing - the Shapley-Sawyer Concentration Class (SSCC) rates globular cluster from most concentrated (I) to least concentrated (XII). The class III NGC104 is the best example of a concentrated cluster, while M55 has a relatively low concentration at XI. M22 and ω Centauri fall in the middle at VII and VIII respectively. The bulk of the best globular clusters can be seen from the Southern hemisphere, with six great examples being circumpolar: NGC104, NGC362, NGC2808, NGC4372, NGC6362 and NGC6752. Whilst I've observed M13 through a small telescope, unfortunately I'm not able to image M13 as it is too far North. All images were captured using the 9" SCT at f/10 and a modified Canon 450D, where the IR filter has been replaced with an IR pass filter, hence increasing red sensitivity and wavelength range.
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