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Simeis 57 has several boring catalog names, but it is popularly known as the Propeller Nebula. It is a small part of the huge Cygnus nebular complex, but it has a recognizable shape. Located about 5,500 ly away, it is a classic emission nebula that, like most of the regions of the Cygnus complex, is dominated by the reddish Halpha emission. In this case, though, the bluish [OIII] emission claims its place and dominates the upper half of this image. This region, as is the case for the whole Cygnus complex, is a place where many new stars are formed. These stars are (or better said, their high energy UV radiation is) responsible to excite the surrounding Hydrogen gas and have it emitting its reddish line at 656.3 nm.
Additional Information
Object
Name(s): Simeis 57
Type: Emission Nebula
RA: 20h 16m 20s
Dec: +43º 39’ 44”
Constellation: Cygnus
Size (arcmin): 25×12 arcmin
Magnitude: ND
Distance: 5,500 ly
Image
Date: 2022-05-15 to 2022-09-22
Location: Curiosity2 Observatory, New Mexico Skies, Mayhill, NM, USA
Size (arcmin): 30×29 arcmin
Telescope: 24” (61 cm) f/6.5 Reflector
Camera: FLI PL16803 (4096x4096pix)
Guiding: Astrodon MonsterMOAG off-axis guider
Total exposure: 31h 40m (Ha: 12h; [OIII]: 10h; [SII]: 6h 40m: RGB: 3h)
Processing: CCDStack, PixInsight (one step) and Photoshop CC 2023