Eta Carinae Nebula

Designation: Caldwell 92, NGC 3372, in constellation of Carina.
Visual magnitude:   +1.0.
Apparent size in arc-minutes: 120′ x 120′.
Diameter in light years: 349.
Distance in light years: 10,000.

One of the most prominent nebulae in the night sky, the Eta Carinae Nebula lies thirty degrees from the South Celestial Pole. It includes several star clusters, the dark Keyhole Nebula and the Homunculus Nebula – the remnants of an outburst from the star Eta Carina nearly two centuries ago.

Here’s an image I took earlier of the Homunculus Nebula. No I didn’t. It’s a Hubble image:

The optical image of Eta Carinae’s made by the Hubble Space Telescope reveals two spectacular bubbles of gas expanding in opposite directions away from a central bright region at speeds in excess of a million miles per hour. The inner region visible in the Chandra image has never been resolved before, and appears to be associated with a central disk of high velocity gas rushing out at much higher speeds perpendicular to the bipolar optical nebula. (Source: Wikimedia Commons)

This is my first two hour exposure and I think it helped bring out some of the detail. With twilight ending at 9.20 pm and the still bright Last Quarter Moon rising at 11.20 pm that was all I had available.

It was great to be outside again under a clear night sky, after nearly three months of raging bush-fires – which were mostly doused by torrential rain last week. Only twenty-three fires are still burning in NSW now – and they are all classified as “under control”. The wind and rain has swept away the hazardous air pollution at last!

The “imaging holiday” has enabled me to improve some methodology.

One improvement I’ve made is subtracting flat/bias frames for the first time, as many of my images have been showing signs of pollution from dust particles. The following image shows the flat image taken just prior to my imaging session:

Dirty! the flat/bias frame, which was subtracted from the stacked light frames to obtain the final image.

This crud in my optics has been showing up on all of my images recently and hopefully I can make it a thing of the past, by improving my flat subtraction technique and making it part of the regular setup routine.

I’ve also made some improvements to my polar aligning techniques, lubricating the mount to smooth the alt-az adjustments and swapping my PoleMaster camera and software for the polar aligment routine in SharpCap.

The latter was forced on me after replacing my old lap-top with a new one, only to find the PoleMaster camera and software wouldn’t work properly on the new one. I’ve reported this to QHYCCD but don’t hold out much chance of a favourable outcome anytime soon, with China in a lock-down over the Corona Virus Covid-19.

However the result using SharpCap was the most accurate polar alignment I’ve ever had, with SharpCap telling me the alignment achieved was 00° 00′ 06″. If I can do that every time, I’ll be happy!

Image Details
Date:  2020-02-14Sky brightness (e/px/sec): 0.89
Exposure: 68×106.6 sec = 120 min.Gain setting:   10
Camera: ZWO ASI 071 MC ProType: CMOS 28.4mm 16 Mpx

Location:  outer suburban. Conditions:  clear sky, no Moon

This image was not cropped.

My images are captured with Sharpcap-pro software using the live-stacking feature, with dark subtraction and in-the-field image processing. Guiding by PHD2, using Orion 80mm guide scope and ZWO ASI120 camera. Image post-processing is carried out using GIMP freeware.

Also in image:
Follow this link to see my image with annotated overlay.

Telescope Details
SkyWatcher Esprit 120 mm apochromatic 3-element refractor.
840 mm focal length @ f/7 with field flattener.
Baader L-Booster UHC-S light pollution filter 2458276.
SkyWatcher EQ6-R Pro mount, with a polar error of 00′ 06″
ZWO ASI120 guide camera, using PHD2 software.
QHYCCD PoleMaster polar aligning camera.
2018-03-10 Telescope & Roger

Images © Roger Powell

I’m one of the founder members of Macarthur Astronomical Society, Australia. 🙃

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=80(Auto)
Frame Rate Limit=Maximum
Timestamp Frames=Off
White Bal (B)=99
White Bal (R)=60
Cooler Power=86
Target Temperature=-10
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Anti Dew Heater=On
Banding Threshold=35
Banding Suppression=0
Apply Flat=C:\Users\powel\Desktop\SharpCap Captures\2020-02-14\Capture\flats\20_28_31.png
Subtract Dark=C:\Users\powel\Desktop\SharpCap Captures\darks\ZWO ASI071MC Pro\RAW16@4944×3284\106.6s\gain_10\dark_6_frames_-10.0C_2020-02-14T10_27_56.png
Black Point
Display Black Point=0
MidTone Point
Display MidTone Point=0.5
White Point
Display White Point=1


  1. Hi Roger
    Yes I get the same thing, dust bunny’s – getting the flat exposure right is the difficult part, I aim for a peak 3/4 of the way across the histogram, however I have recently started using the Flats Aid in APT and this seems to work just as well. I’m glad to hear that the fires are coming under control at last thanks to the rain you have had, here in the UK we have had storm Ciara last weekend and now storm Dennis this weekend, I have done no more work on the Rosette nebula mosaic, I think by the time this cloudy rainy muck clears up it will be 2020 before I do any more to it, soon it will be below the horizon and the darkness hours become shorter.


    1. I need to include flat frames in my routine. It was during early twilight when I took this, my first ever, flat. I just quickly pointed at some clear blue western sky and hoped for the best. It resulted in a false light gradient. I need to do better and I know there are better methods to explore.

      It must be very disappointing to be stuck half way through your Rosette project, knowing that you may need to shelve it for another year. At your latitude you don’t get much darkness in Summer.


      1. I use an Ultrathin Light Pad Art Tracing Board in B4 size fortaking flats, it has 3 light settings, I use the lowest setting. Yes the weather is still rubbish and yet another storm ( Jorge ) last weekend.

        Liked by 1 person

      2. Thanks, Will. Since I posted above, I did exactly that, except I bought an A4 size. I’ve had two home astro-sessions since then and it seems a very simple procedure but although it seems to have reduced the dust, it still hasn’t completely eliminated it. Probably I need more frames to build the master flat.


  2. That is a beautiful image. Our skies are not cooperating here in the mid-US. Plus it has been cold. Yesterday dawned about -12˚F. I don’t go out in that. But, the sky was clear for a while. 🙂

    Liked by 1 person

  3. Hi Roger,
    Glad you are back posting great pictures. I am having issues with my laptop, so you may get 2 posted comments. Sorry about that. I am super happy the bush fires are under control.
    Cheers, Fran


    1. Tried it once but need to have another go now the air pollution from the fires has gone.
      However, subtracting flat frames is standard practice in astronomy, I’ve just been slow on the uptake.

      Liked by 1 person

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