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Contains:  M 13, Great Cluster in Hercules, NGC 6205
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M13: The Great Globular Cluster in Hercules, 


            Robert Churan
M13: The Great Globular Cluster in Hercules

M13: The Great Globular Cluster in Hercules

Technical card

Resolution: 5200x3500

ZWO Blue 1.25": 10x256"
ZWO Green 1.25": 10x256"
ZWO Luminance 1.25": 29x256"
ZWO Red 1.25": 10x256"

Integration: 4.2 hours

Darks: ~50

Flats: ~50

Bias: ~50 job: 2717708

RA center: 250.408 degrees

DEC center: 36.447 degrees

Pixel scale: 0.379 arcsec/pixel

Orientation: 0.218 degrees

Field radius: 0.330 degrees

Data source: Backyard


Messier 13 is a bright globular cluster of apparent magnitude 5.8 located 25,100 light years away in the northern constellation of Hercules. The magnitude of 5.8 makes the cluster visible to the unaided eye in clear, dark skies. It also means I could knock this target off comfortably in one night with only 4.2 hours of integration time.

The cluster is 145 light years across and contains hundreds of thousands of stars, the brightest being the variable red giant star V11. The density of stars in M13 is more than a hundred times the stellar density in the neighborhood around out own solar system. This stellar density will sometimes cause collisions and form the blue stars in the image known as "blue stragglers."

The designation of "blue stragglers" comes from the fact that blue stars have very short lifespans. However, the cluster has been dated to 11.65 billion years old, making it not much younger than the universe itself. This abundance of young stars in and older cluster makes M13 a very interesting target for astronomers the world over.

This bright cluster was a fun and quick image. Short integration time without many subframes. I called my first version final because of how well it turned out. The only problem was in guiding. My DEC was fine, but RA was bonkers. Recently, I've been having spikes in RA that don't seem to have a cause. RA will be smooth and no guide commands will be issued. Then, a sudden jump in RA east or west by about 3-4 seconds of arc and PHD2 rushes to get the star back. The error isn't periodic and I've tried all 9 combinations of balance (Ra east heavy, west heavy, and perfect balance with DEC front heavy, back heavy, and perfect balance) and redone my cables as well as going over all PHD2 settings controlling RA, but nothing is affecting the RA spikes. I figure it is likely an issue with mount mechanics but I'd rather not bust open the mount, as the stars still look okay in the image. If anyone has had this issue on AVX or another mount, or even an idea, I'd love to hear it. Maybe it'll fix my guiding. Thanks & Clear Skies to all :)



Robert Churan
License: None (All rights reserved)

Sky plot

Sky plot


M13: The Great Globular Cluster in Hercules, 


            Robert Churan