The Medusa Nebula, Abell 21 (PK205+14.1, Sh2-274)

 Posted: 2 Sep, 2020
The Medusa Nebula, Abell 21 (PK205+14.1, Sh2-274)
Objects: Less More
Technical Info
Telescope or Lens: 8" Celestron Schmidt-Cassegrain CPC800 GPS (XLT)
Camera: Starlight Xpress Trius SX694
Mount: equatorial wedge
Guide Scope: Baader 61x250mm
Guide Camera: ASI120MM
Software: MaxIm DL6, PHD2, PixInsight, StarTools, Photoshop CC, Zoner photo studio 14
Accessories: reducer Starizona Night Owl 0.4х, filters Astrodon LRGB E-series gen 2, Astrodon Ha 5nm, Astrodon OIII 3nm
Exposure:
90 x 150" ISO/Gain: 0 - Astrodon L
43 x 150" ISO/Gain: 0 - Astrodon R
43 x 150" ISO/Gain: 0 - Astrodon G
43 x 150" ISO/Gain: 0 - Astrodon B
52 x 600" ISO/Gain: 0 - Astrodon Ha 5nm
83 x 600" ISO/Gain: 0 - Astrodon OIII 3nm
Yellow zoneLight Pollution:
 Chervonograd, Ukraine
31 h 38 m
1072
The Medusa Nebula, Abell 21 (PK205+14.1, Sh2-274) is a planetary nebula in the constellation of Gemini.
Although Abell 21 has a large apparent diameter of 10 arcminutes, its surface brightness is so low, with features ranging from magnitude 16-25 and was originally discovered in 1955 by UCLA astronomer George O. Abell. It is a planetary nebula lying at a distance of 1,500 light-years, which gives it an estimated diameter of 4 light-years. The parent star, now a white dwarf, is thought to be the blue star near the center of the crescent. The braided filaments of the shell the star shed during its red giant phase resemble the serpents that comprise the hair of Medusa, giving the nebula its popular name, the Medusa Nebula. Beyond the beautiful braided crescent, additional hydrogen-alpha nebulosity, shed earlier by the star, can be seen at the center right and upper right corner of the image.

This image taken over several nights in March, April 2020.
L-channel - 90 x 150 sec. bin 1x1;
R-channel - 43 x 150 sec. bin 1x1;
G-channel - 43 x 150 sec. bin 1x1;
B-channel - 43 x 150 sec. bin 1x1;
Ha- 52 x 600 sec. bin 1x1;
OIII- 83 x 600 sec. bin 1x1.
Total integration time about 31:37 hours.
Resolution: 1869x1682 px
Scale: 2760 KB
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