Sh2-274 (Abell 21)
About image
Sh2-274, also catalogued as Abell 21, is a planetary nebula in Gemini costellation.
Its shape - a tangle of luminous filaments oriented to form a sort of semicircle open on one side - makes it very similar to a supernova remnant, so much so that it was initially considered as such.
Subsequently, through measurements of its emissions and its expansion rate, it was discovered that it belongs to the class of planetary nebulae, albeit at an advanced stage due to its age, estimated at around 8,800 years. The distance from Earth is about 1500 light years.
The nebula is quite bright, but the external nebulosity blue/red in the upper left side of the image is quite faint, so in order to not lose it I preferred to take the sky luminosity a little higher than my “standard”.
Technical data
Optic GSO RC12 Truss - Aperture 304mm, focal lenght 2432mm, f/8
Mount 10Micron GM2000 HPSII
Camera ZWO ASI 2600MM Pro with external filter wheel for Ha/OIII
Filters Astrodon Gen2 E-Serie Tru-Balance 50mm unmounted RGB , Astrodon 50mm narrowband filters Ha 5nm and OIII 5nm
Guiding system OAG-L ZWO with guide camera ASI 174 Mini
Exposure details R 12x120" bin3 -15C gain 100
G 12x120" bin3 -15C gain 100
B 12x120" bin3 -15C gain 100
Ha 42x300" bin3 -15C gain 100
OIII 50x300" bin3 -15C gain 100
Total integration 8h12'
Acquisition Voyager, PHD2
Processing Pixinsight 1.8, Photoshop CS5, BlurXTerminator, NoiseXTerminator, StarXTerminator
SQM-L 20.98
Location Promiod (Aosta Valley, Italy), own remote observatory
Date 12/13/14 December 2025
© Roberto Marinoni 2019 - All rights reserved