Prawn Nebula

IC 4628, a bright H II (ionised atomic hydrogen) emission nebula in Scorpius, is more than seventy light years in width. It is commonly called the Prawn Nebula. The bright newly formed stars in the nebula emit ultra-violet light which ionises the hydrogen gas and causes it to glow.

Also in the image is Trumpler 24, a widely scattered cluster of over a hundred stars, which extends beyond the lower border of this image.

This thirty minute image was the third and final one I took during a very cold seven hour field night with Macarthur Astronomical Society, as the Moon was sliding below the horizon towards the end of the session.  The next field trip will likely be less cold as the southern Spring Equinox approaches but the sun will be setting later and shortening the session, as we usually depart by midnight.

All equipment, including the laptop, functioned well and I found that lubricating my alt-az bolts helped improve my polar alignment error to 22 arc-seconds. Let’s see if I can improve on that next time. More oil!   😛

Last time I tried IC 4628 was a disaster compared to this!

Object Details:

Designation: IC 4628, Gum 56.
Constellation: Scorpius.
Visual magnitude:  +10.0
Apparent size:  90′ x 60′
Diameter:  70.9 light years.
Distance:   2,700 light years.
Altitude during exposure:  53° above SSW horizon.
Also in image: Open star cluster Trumpler 24.

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Please feel free to jump past the technical stuff:

Image: Exposure: 21  x 89 sec = 31 min. Gain: 270 Date:  2019-08-06 Location:  semi-dark rural. Conditions:  clear Moon: 5 days old, set 11.00 pm

Processing: Image acquisition:  SharpCap. Method: Live stacked. Darks: 10x Image post-processing:  GIMP. Cropping:   No Sky:   0.29  e/pixel/s .

Gear:

Telescope:	SkyWatcher Esprit	Type:	120ED 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: N	Guiding:	No
Polar aligning:	QHYCCD PoleMaster	Polar Error:	00’ 22”

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=1 every 4 seconds Gain=270 Exposure=89 Timestamp Frames=Off White Bal (B)=50 White Bal (R)=53 Brightness=40 Temperature=-4.9 Cooler Power=100 Target Temperature=-15 Cooler=On Auto Exp Max Gain=300 Auto Exp Max Exp M S=30000

Auto Exp Target Brightness=100Mono Bin=Off Anti Dew Heater=OffBanding Threshold=35 Banding Suppression=0Apply Flat=None Subtract Dark=C:\Users\Roger\Desktop\SharpCap Captures\darks\ZWO ASI071MC Pro\RAW16@4944×3284\89.4s\gain_270\dark_10_frames_-0.8C_2019-08-06T09_39_54.fits #Black Point Display Black Point=0.01953125 #MidTone Point Display MidTone Point=0.43120698664032 #White Point Display White Point=0.998046875 TimeStamp=2019-08-06T13:27:42.2267364Z SharpCapVersion=3.2.6062.0 TotalExposure(s)=1869 StackedFrames=21

Image © Roger Powell

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