The Nine Best Globular Clusters (Warwick)

The Nine Best Globular Clusters

I was out with Canberra Astronomical Society last week and we were looking at Omega Centauri (NGC5139). It was a terrific view and filled the eyepiece. We noticed that M13 "The Great Globular Cluster in Hercules" was low in the north, so we turned one of our telescopes around. I was surprised that M13 only half filled the eyepiece and was considerably dimmer than Omega Centauri. This got me wondering how M13 compares to other globular cluster. A list I found suggested that M13 was the ninth largest globular cluster by angular diameter. I then noticed that all nine are currently visible in the southern hemisphere. So I imaged all nine and put them together in this composite for comparison. I used short exposures because I was shooting from my backyard at Bortle 6. I was careful to use the same equipment and batch crop to preserve the image scale of each cluster.

M13 is a spectacular and beautiful object and I don’t think angular diameter is a fair measure of its quality. It is richer than its angular size. But, compared to the two southern clusters in Centaurus and Tucana perhaps the nomenclature “Great” is a little overstated.

In this composite the clusters from left to right and top to bottom are:

Please note: The following tables are updated every 24 hours.

Distribution of astrophotographers

This table shows the number of distinct astrophotographers who have been assigned and IOTD/TP award compared to the total number of images awarded.
	Distinct awarded users	Total awarded images
Image of the day
Top picks
Top pick nominations

Distribution of subject types

This table shows the distribution of awards per subject type, compared to the popularity of images of that subject type.
	Image of the day	Top pick	Top pick nominations	Total submitted
Deep sky
Solar system
Extremely wide field
Star trails
Northern lights
Noctilucent clouds
Landscape

Distribution of data sources

This table shows the distribution of awards per data source, compared to the popularity of images acquired from that data source.
	Image of the day	Top pick	Top pick nominations	Total submitted
Backyard
Traveller
Own remote observatory
Amateur hosting facility
Public amaeteur data
Professional, scientific grade data
Mix of multiple sources
Other
Unknown

The “AstroBin Image of the Day and Top Picks”, or IOTD/TP, is a long-running system to promote beautiful, interesting, peculiar, or otherwise amazing astrophotographs, with a focus on technical excellence. Learn more.

Submitted The date and time when you submitted this image for IOTD/TP consideration.	...
Views by Submitters (available since September 19th, 2023) Every image is assigned to 50% of available Submitters. In the event that at least 80% of them don't view the image before its time in the IOTD/TP process expires, it's assigned to the other 50% of Submitters and the process begins anew.
Promotions by Submitters When 3 distinct Submitters promote the image, it moves on to the next stage of the process: evaluation for Top Pick status. This requirement, in addition to anonymization of images and distribution to only a subset of them, prevents biases and ensures that the best images are selected.
Promotions by Reviewers When 3 distinct Reviewers promote the image, it moves on to the next stage of the process: evaluation for IOTD status.
Early dismissal Staff members have a lot of images to inspect on a daily basis, and they can dismiss images if they believe they don't meet the requirements for IOTD/TP selection. If an image is dismissed 5 times, it's removed from the process. This streamlines the process and ensures that any bias present in promotions could be overruled by other staff members.

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