IC 4685

Nebula in Sagittarius

5.1 light years.
1,800 light years.
Apparent size:
10 arc min

The emission nebula IC4685 is a bright nebula in Sagittarius, right near the edge of the more renowned Lagoon Nebula M8. After a few nights using my uncooled planetary camera, I went back to my cooled deep sky camera, with its wider field of view. However, it was a night of two big mistakes, where I didn’t follow my own check list.

I took two images during the session.

The first target was the IC 4685 nebula (above), imaged in hydrogen alpha – and Blunder No 1 was forgetting to activate the cooler on the camera. So instead of running the camera at a setting below zero, the camera operated at +18° C. This resulted in a degraded image, some of which was repairable during image processing.

2 hours
Field of View:
1.52 ° x 1.0 °
Image date:

The second target was globular cluster NGC 5139 or Omega Centauri, a favourite which I haven’t imaged for a couple of years. Whilst targeting this object I turned off the guiding – and Blunder No 2 was forgetting to turn it back on when I began live stacking the images. The result was loss of star sharpness and an image which I could not publish full size as the defects were too obvious:

Exposure: 25 minutes, Field of View: 1.55 ° x 1.02 °
Image date: 2021-07-05

I keep a standard check list of procedures to tick off as I set up the telescope and prepare for imaging. I suppose Blunder No 3 was not including Blunders 1 & 2 on the check list…… 😳

At the time, everything appeared to be going very smoothly and I was oblivious of my indiscretions, so while taking the above images I decided to amuse myself with my DSLR on a tripod.

Saturn (magnitude +0.4) at the very top of the image below was looking quite modest in comparison with Jupiter (8 times brighter at mag. -2.7), which was rising in the East and looking particularly bright:

Looking East
Saturn (top) and the stars of Capricornus.
Jupiter (bottom) and the stars of Aquarius.

Image: 10 seconds, f/4.5, ISO 640

The next image below is pointing towards the light pollution dome of metropolitan Sydney. The left edge of the image is roughly due North and the very bright star is Vega (mag. +0.02).

In studying this image I found a very interesting object which I hope to image with my telescope next time out, so watch this space!

The House on the Hill
Northerly view showing Vega in Lyra (left)
Image: 2 seconds, f/1.8, ISO 500

Finally, I utilised the unwanted over-illumination from the nearby street light, plus my neighbours rear extension lighting across the road and an up-shining torch below the tripod, to present the Cosmic Focus Observatory in action:

Imaging under way!
Image: 62 seconds
, f/8, ISO 400
No blunders taking this image!

Location of Sagittarius

Image: Wikimedia Commons


Thanks for reading 🙃

Telescope & Imaging Details

Telescope:SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.
Optics:Field flattener; ZWO Duo-band Hα (656nm) and [OIII] (500nm) filter.
Mount & Guiding:SkyWatcher EQ6-R Pro mount; ZWO ASI120 guide camera.
Imaging camera: ZWO ASI 071 MC cooled.
Software:Control: Cartes du Ciel, ASCOM, EQMOD, PHD2. Imaging processing: SharpCap, Gimp.
Observatory:34° South.

Images © Roger Powell

I’m one of the founder members of Macarthur Astronomical Society and current webmaster.


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