Messier 13

The Great Hercules Cluster.

I’ve heard it said that when you’ve seen one globular cluster, then you’ve seen them all. I guess there’s some element of truth in that but I wanted to image M13, reputedly the best globular cluster in the Northern Hemisphere. It’s 6,000 light years further away than our glorious Southern  Omega Centauri and about half it’s physical diameter, so I didn’t expect too much.

It’s still a magnificent object, though, composed of hundreds of thousands of stars.

It’s a large  globular cluster, visible here in Sydney at a maximum height of 20° above the northern horizon. When I began imaging, it was already heading downwards through Sydney’s light glow towards a neighbour’s tree and I decided to use my long neglected Baader UHC-S dual band light pollution filter. (Goodness knows why I haven’t been using it recently, as my suburban sky continues to deteriorate).

Perhaps now that I’ve seen M13, Omega Centauri and 47-Tucanae I’ve seen them all……………

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Time for a moan.

The current lunar cycle began last week with a number of consecutive clear nights and guess what?

 ✔ Night one: Clear. I managed to get the above image and a few frames of M16 before the Moon rose.

❌ Night two:  Clear – but a disaster as my laptop (or the SharpCap software, I’m not sure which) dropped every single image frame and I packed up with nothing imaged.   😨 

❌ Night 3: a  bit cloudy so I stayed indoors.  🤓 

❌❌❌❌ Nights 4-7: all clear nights – but I found myself house-bound with a nasty head cold and missed out on a field night too. 😵 

❓ Now recovered and of course the forecast is less promising for the rest of the cycle. Not happy!  😖

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Object Details:

Designation: M13, The Hercules Cluster, NGC 6205
Constellation: Hercules
Visual magnitude:  +5.8
Apparent size:  20′
Diameter:  135 light years.
Distance:  23,000 light years.
Altitude during exposure:  16° above NNW horizon.

Also Visible:

Red giant star HD150998 (near top).

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Technical stuff below.
Please feel free to jump to the end and like or comment.

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Image:

Exposure:  26 min (52 frames 29.8 sec)
Gain: 128
Date:  2019-07-22
Location:  Outer suburban.
Conditions:  clear.
Moon: rise 10.00 pm.
Sky:  1.77 e/pixel/s  

Processing:

Image acquisition software:  SharpCap, live stacked.
Image post-processing:  GIMP.
Cropping: two edges, to centre the object.

Gear:

Telescope:	SkyWatcher Esprit	Type:	120ED triplet refractor
Focal:	840 mm F/7	Mount:	SkyWatcher EQ6-R Pro
Camera:	ZWO ASI 071 MC Pro	Type:	CMOS 28.4mm 16 Mpx
Optical aids:	Flattener: Y; filter: LP	Guiding:	No
Polar aligning:	QHYCCD PoleMaster	Polar Error:	02’ 26”

Geek Log:

[ZWO ASI071MC Pro]
Debayer Preview=On
Output Format=FITS files (*.fits)
Binning=1
Capture Area=4944×3284
Colour Space=RAW16
Hardware Binning=Off
Turbo USB=40
Flip=None
Frame Rate Limit=Maximum
Gain=128
Exposure=29.802489
Timestamp Frames=Off
White Bal (B)=60
White Bal (R)=60
Brightness=16
Temperature=-15.4
Cooler Power=61
Target Temperature=-15
Cooler=On
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Anti Dew Heater=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.327798941363283
#White Point
Display White Point=0.910970869974874
TimeStamp=2019-07-22T12:19:14.7064483Z
SharpCapVersion=3.2.5986.0
TotalExposure(s)=1549.729428
StackedFrames=52

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Image © Roger Powell

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