Hemisphere:  Northern  ·  Constellation: Hercules (Her)  ·  Contains:  Great Cluster in Hercules  ·  M 13  ·  NGC 6205  ·  NGC 6207
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M13 - Great Globular Cluster in Hercules, 


            Andrew Klinger
M13 - Great Globular Cluster in Hercules
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M13 - Great Globular Cluster in Hercules

Technical card

Imaging telescopes or lenses: William Optics GT-81

Imaging cameras: ZWO ASI1600MM-Cool

Mounts: Orion Sirius EQ-G (HEQ5)

Guiding telescopes or lenses: Orion 50 mm Guide Scope

Guiding cameras: Orion Star Shoot Auto Guider

Focal reducers: William Optics Flat 6A

Software: Sequence Generator Pro  ·  PHD2  ·  Cartes du Ciel  ·  EQMOD  ·  PixInsight

Filters: ZWO B 1.25"  ·  ZWO G 1.25"  ·  ZWO R 1.25"

Accessory: PoleMaster

Dates:April 1, 2019

ZWO B 1.25": 23x180" (gain: 76.00) -20C bin 1x1
ZWO G 1.25": 23x180" (gain: 76.00) -20C bin 1x1
ZWO R 1.25": 24x180" (gain: 76.00) -20C bin 1x1

Integration: 3.5 hours

Darks: ~64

Flats: ~30

Bias: ~200

Avg. Moon age: 26.01 days

Avg. Moon phase: 13.39%

Bortle Dark-Sky Scale: 3.00

Basic astrometry details

Astrometry.net job: 2665206

RA center: 16h 41' 41"

DEC center: +36° 27' 18"

Pixel scale: 1.353 arcsec/pixel

Orientation: 9.649 degrees

Field radius: 0.611 degrees

Resolution: 2301x2301

Data source: Traveller


One of the larger globular star clusters in the sky, M13 is home to over 100,000 stars.

This is a fairly large crop with my system. I shot this target a partial night to test a stop-down ring for my scope. The ring slightly improves some optical issues I've been dealing with on my stars.

OTA: William Optics GT81 w/Flat6A (382mm fl at f/4.7)
74mm aperture stop-down ring (brings scope to f/5.2)
Mount: Orion Sirius EQ-G (HEQ-5)
Guidescope: Orion 50mm guidescope
Guiding camera: Orion StarShoot Autoguider
Imaging camera: ZWO ASI1600MM-Cool


Location: Ft Griffin State Historic Park, TX (Bortle 3)
Dates: 4/1/19
Gain: 76 Offset: 15
Camera temp: -20C
R: 24x180"
G: 23x180"
B: 23x180"
Total integration time: 3hr 30min
64x darks per calibration (master from library)
30x flats per calibration
200x bias per calibration (master from library)

Batch PreProcessing script to generate calibrated images
StarAlignment to register all frames to the reference
LocalNormalization of all registered frames
DynamicCrop each master
DBE each master

RGB Processing:
TGV and MMT noise reduction (via Jon Rista's method)
LinearFit to Blue
Extracted Luminance channel and set aside for processing
ArcsinhStretch x2
SCNR green
CurvesTransformation for saturation
ColorSaturation to target blues

L Processing:
Arcsinhstretch x2

Combined L and RGB with LRGBCombination tool
CurvesTransformation to balance background
SCNR green
Resampled to 75% for web posting


Sky plot

Sky plot


M13 - Great Globular Cluster in Hercules, 


            Andrew Klinger