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)

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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.

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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.

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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!

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Image Details

Date:  2020-02-14	Sky brightness (e/px/sec): 0.89
Exposure: 68×106.6 sec = 120 min.	Gain setting:   10
Camera: ZWO ASI 071 MC Pro	Type: 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.

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

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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.

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Images © Roger Powell

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

Geek Log

[ZWO ASI071MC Pro] Debayer Preview=On Pan=0 Tilt=0 Output Format=FITS files (*.fits) Binning=1 Capture Area=4944×3284 Colour Space=RAW16 Hardware Binning=Off Turbo USB=80(Auto) Flip=None Frame Rate Limit=Maximum Gain=10 Exposure=106.630379 Timestamp Frames=Off White Bal (B)=99 White Bal (R)=60 Brightness=4 Temperature=-10 Cooler Power=86 Target Temperature=-10 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=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 TimeStamp=2020-02-14T12:34:53.8186058Z SharpCapVersion=3.2.6173.0 TotalExposure(s)=7250.865772 StackedFrames=68

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