The Great Hercules Cluster (M13) stands as one of the most spectacular globular star clusters visible from Earth. For astrophotographers seeking a challenging yet rewarding summer target, this magnificent stellar collection offers breathtaking detail and scientific wonder.
Why the Hercules Globular Cluster is Perfect for Summer Imaging
During June and July, when many deep-sky objects are poorly positioned, the Great Hercules Cluster reaches its prime viewing altitude. While other globular clusters like M10, M5, and M92 are available, M13 remains the most sought-after globular cluster of the summer night sky.
Located in the constellation Hercules, the Great Hercules Cluster contains over 300,000 stars packed into a sphere roughly 145 light-years across. At an apparent magnitude of 5.8, it’s visible to the naked eye under dark skies. Photographing this at F10 on a Celestron Edge HD 8″ is not much of an issue. Might as well take advantage of that telescope‘s full 2032mm and get a fantastic close-up revealing the color, depth, and energy of M13.
Astrophotography Equipment Considerations for The Great Hercules Cluster
Focal Length Requirements
The Great Hercules Cluster spans approximately 20 arcminutes, making it suitable for moderate focal lengths. My 805mm telescope paired with an ASI533MM camera provides adequate resolution to capture the cluster‘s intricate structure, though a Celestron 8-inch EdgeHD at 2032mm at f10 would offer superior detail.
Camera Setup
For optimal Great Hercules Cluster imaging:
While this can be captured in 2-3 hours due to its bright stars, I would plan for extended exposure times (8-10+ hours total) to capture more detail.
Balance luminance and RGB data collection. With mono, luminance should be the same amount of time as your R,G, and B data combined.
Processing the Great Hercules Cluster: My Step-by-Step Workflow
Initial Calibration
Dynamic Crop – Remove edge artifacts
Dynamic Background Extraction – Flatten the background
Deconvolution – Sharpen star detail (I use Blur Xterminator)
RGB Processing
Combine individual color channels using channel combination
Use multiscale linear transform (MLT) for noise reduction
Perform a histogram transformation to transform it into a nonlinear state
Final Integration
Combine RGB and luminance data using LRGB combination
Use various curves transformations to bring out color, luminance, and contrast.
Enhance star colors with color saturation OR curves transformation
Crop to optimize composition
The Difference More Data Makes
Extended exposure times dramatically improve Great Hercules Cluster images:
Enhanced Detail: Additional hours reveal the background galaxy NGC 6207, adding interest to the composition.
Improved Color: Extended RGB exposure brings out subtle star colors throughout the cluster, from cool blue giants to warm red stars.
Increased Star Count: Longer exposures penetrate deeper into the cluster‘s dense core, revealing thousands of additional faint stars.
Better Signal-to-Noise: Extended integration time reduces noise, allowing for more aggressive processing without artifacts.
Alternative Summer Targets
While the Great Hercules Cluster dominates summer globular cluster photography, consider these alternatives:
M10 and M5 offer larger apparent sizes for wide-field setups
Rho Ophiuchi provides colorful nebulosity for southern observers
M92 presents a challenging but rewarding alternative in Hercules
Planning Your Great Hercules Cluster Session
Best Viewing Months: June through August
Optimal Time: 10 PM to 2 AM local time
Minimum Exposure: 5+ hours for detailed results
Recommended Total: 8-10 hours for quality images
The Great Hercules Cluster rewards patience and planning. Each additional hour of data reveals new stellar details and enhances the overall impact of this magnificent cosmic landmark.
Whether you’re capturing M13 for the first time or returning to improve previous attempts, the Great Hercules Cluster offers endless opportunities for discovery and artistic expression in astrophotography.
