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.

Please feel free to jump past the technical stuff:


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


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


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
Output Format=FITS files (*.fits)
Capture Area=4944×3284
Colour Space=RAW16
Hardware Binning=Off
Turbo USB=40
Frame Rate Limit=1 every 4 seconds
Timestamp Frames=Off
White Bal (B)=50
White Bal (R)=53
Cooler Power=100
Target Temperature=-15
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

Image © Roger Powell



Leave a comment or ask a question . . . .

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s