Flocculent Galaxy NGC 7793

Object Details:

Designation:    NGC 7793    
Constellation:  Sculptor
Visual magnitude:   +9.2
Apparent size:   10.4′ x 6.0′
Diameter:   37,000 light years.
Distance:    12 million light years


NGC 7793 is a flocculent galaxy, which means it looks fluffy and has discontinuous spiral arms. I have to admit I did not know that, so I put it the title so I might remember it.

The galaxy, a dwarf spiral, is one of thirteen galaxies in the Sculptor Group of galaxies – a group of galaxies fairly “close” to the Local Group, as shown below:

Nearby Galaxy Groups
A three-dimensional representation of nearby clusters of galaxies, with our own cluster, called the Local Group, in the centre, along with the nearby Sculptor group. (ANDREW Z. COLVIN)

A clear sky was forecast for this field trip with Macarthur Astronomical Society but as luck would have it, three new large bushfires started up to our west and we were “treated” to plumes of smoke drifting around the west and north, about 30° above the horizon.

However, the rest of the sky was clear and when I picked NGC 7793 from my target list, it was because it was high in the sky and had just passed over the meridian, well away from the smoke.

That was five nights ago and these fires are still burning in the wilderness of Yerranderie State Conservation Area and beyond, less than fifteen kilometres away from our astro-observing site.

At home today, visibility due to the constant smoke haze has been down to about six kilometres and we have been advised by authorities to stay indoors where possible. They’ve been saying that for the last three weeks….  😟

2019-12-02 Bushfires
Bushfires in Yerranderie and Kanangra-Boyd regions: status at 2019-12-02. Our observing site is at The Oaks. (Source: NSW Rural Fire Service).

Technical stuff:

Image & Processing:

Date:  2019-11-27
Exposure:   32 x 143 sec  =  76 min.
Gain:  230.
Conditions:  bushfire smoke 30° above horizon to west, north and east, from out of control bushfires.

Location:  semi-dark rural.
Sky: mostly clear but occasional minor high cloud.
Wind: fairly calm.
Sky brightness:   0.21 e/pixel/sec .
Temp Min: 14°

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

Image post-processing:  GIMP.
Cropping: Yes

Gear:

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
Polar aligning: QHYCCD PoleMaster Polar Error: 1’ 59”

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=40
Flip=None
Frame Rate Limit=8 fps
Gain=230
Exposure=143
Timestamp Frames=Off
White Bal (B)=50
White Bal (R)=53
Brightness=16
Temperature=-4.9
Cooler Power=32
Target Temperature=-5
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=None
Subtract Dark=C:\Users\Roger\Desktop\SharpCap Captures\darks\ZWO ASI071MC Pro\RAW16@4944×3284\142.7s\gain_230\dark_5_frames_-10.0C_2019-11-27T10_22_52.fits
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1
TimeStamp=2019-11-27T12:21:16.6596731Z
SharpCapVersion=3.2.6086.0
TotalExposure(s)=4576
StackedFrames=32

See my image with Astrometry.net annotated overlay.

Images © Roger Powell

2018-03-10 Telescope & Roger

 

5 Comments

  1. Sorry to hear a about the continuing fires, particularily with it’s effect on your quest for clear skies. It is brought up often on news media here in the states. That and your occasional neighbors porch light can be frustrating for those of us who cherish those clear, dark skies.

    Like

    1. We’d been clear of serious bushfires locally until these fires started up last week but the smoke has been here for several weeks. I think it may be here all summer.

      Like

  2. Is summer an extra dry season? I listen carefully to reports here and think about all those courageous firefighters. You too of course. Thanks for posting. Fran

    Like

    1. Hi Fran,

      Yes it is extra dry here in New South Wales. Rain is scarce, humidity is low and temperature records are regularly broken. Country regions are in a drought emergency – rivers and dams are drying up, fish are dying, farmers are losing crops and are unable to feed livestock.

      The hot, dry conditions are consistent with what climate scientists have been predicting and it means stronger bushfires occurring more often. Hats off to the firefighters in the NSW Rural Fire Service – they are all volunteers.

      Like

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