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……………
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! 😖
Designation: M13, The Hercules Cluster, NGC 6205
Visual magnitude: +5.8
Apparent size: 20′
Diameter: 135 light years.
Distance: 23,000 light years.
Altitude during exposure: 16° above NNW horizon.
Red giant star HD150998 (near top).
Technical stuff below.
Please feel free to jump to the end and like or comment.
Exposure: 26 min (52 frames 29.8 sec)
Location: Outer suburban.
Moon: rise 10.00 pm.
Sky: 1.77 e/pixel/s
Image acquisition software: SharpCap, live stacked.
Image post-processing: GIMP.
Cropping: two edges, to centre the object.
|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”|
[ZWO ASI071MC Pro]
Output Format=FITS files (*.fits)
Frame Rate Limit=Maximum
White Bal (B)=60
White Bal (R)=60
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Anti Dew Heater=Off
Display Black Point=0
Display MidTone Point=0.327798941363283
Display White Point=0.910970869974874
Image © Roger Powell