Globular Cluster NGC 6752

Object Details:

Designations:  NGC 6752, Caldwell 93.    Constellation: Pavo.
Visual magnitude:   +5.4                            Apparent size:    29′
Diameter:   110 light years.                      Distance:   13,000 light years

NGC 6752 is one of several globular clusters which I’ve imaged over recent months. It’s listed as Object 93 on the Caldwell Catalogue, which was prepared by the late Sir Patrick Moore, consisting of bright objects which were not included on the more well-known Messier List.

The Caldwell Catalogue has 109 objects, which, when added to the 110 objects in the Messier list, provides 219 bright targets for amateur astronomers to seek out (about 180 of them visible from my Southerly location).

NGC 6752 is reputed to “hold over 100,000 stars in a sphere about 100 light-years in diameter”. So says Wikipedia.

It is a fairly typical sixth magnitude object with a seventh magnitude nearby star, HD 177999, a blue giant.

Due to its close proximity (galactically speaking) of 13,000 light years, NGC 6752 is the third brightest globular cluster. In case you were wondering, this handy website informs us that, at walking speed, it would take 2,179,504,044,250 years to reach NGC 6752. That’s over 2.1 trillion years with no stopping along the way……

Nine days of this month’s lunar cycle have passed. During that period, the weather here has been mostly cloudy – and when the sky has been clear of clouds, the evenings have been endowed with the worst long-term bush-fire smoke I’ve ever known.

So far, anyway.   😷 😷😷😷😷😷

Most of it came from this gigantic bushfire burning NW of Sydney :

2019-11-22 Wollemi Bushfire
2019-11-22 Wollemi Bushfire – extending 80 km from Glen Alice in the West to Wiseman’s Ferry in the East. It has so far burnt out 185,980 ha.

It is 80 km from one end to the other, so spare a thought for the brave firies working hard to extinguish it.

Even now, the haze is still lingering here in SW Sydney – and meanwhile, further up the coast of NSW, many other huge bushfires are still burning. 😳

About seven lunar cycle nights are left before the Moon gets too bright again. The outlook is poor but I am hoping for at least one clear, smokeless night.

Some might say that is a first world problem.

Technical stuff:

Image & Processing:

Date:  2019-10-17
Exposure:  31 x 89 sec  =  46 min.
Gain:   113

Location:  outer suburban
Conditions:  clear, wind gusts 30-40kph. Moon: rose 10.17 pm.
Sky brightness:   0.66 e/pixel/sec . 

Image acquisition:  SharpCap.
Method: Live stacked.
Darks: 6x

Image post-processing:  GIMP.
Cropping: yes


Telescope: SkyWatcher Esprit  Type: 120 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: Yes/No
Polar aligning: QHYCCD PoleMaster Polar Error: 74”

Geek Log:

[ZWO ASI071MC Pro]
Debayer Preview=On
Output Format=FITS files (*.fits)
Capture Area=4944×3284
Colour Space=RAW16
Hardware Binning=Off
Turbo USB=40
Frame Rate Limit=4 fps
Timestamp Frames=Off
White Bal (B)=50
White Bal (R)=53
Cooler Power=100
Target Temperature=-20
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=C:\Users\Roger\Desktop\SharpCap Captures\darks\ZWO ASI071MC Pro\RAW16@4944×3284\89.4s\gain_113\dark_6_frames_-14.8C_2019-10-17T10_42_24.fits
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1

Also in image:  See my image with annotated overlay.

Images © Roger Powell

2018-03-10 Telescope & Roger





  1. Very good image. Your cloudiness sounds like ours. Yesterday and today are ok. A nice sliver of moon was showing this morning.

    I’ve been reading about those big fires. Is progress being made yet? Fires in Canada and the Colorado Rockies sometimes stream smoke our way. We had a lot of colorful sunrises and sunsets a couple of months ago.


    1. The fires are still burning, Jim. 600 homes lost, several dead. It’s not even summer yet.

      A gap in the clouds seems likely tomorrow, so a quick field trip is being planned.


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