Abell 21 • Sh2-274 • Medusa Planetary Nebula (Douglas J Struble)

Celestial hemisphere: Northern · Constellation: Gemini (Gem)

Abell 21 • Sh2-274 • Medusa Planetary Nebula, Douglas J Struble

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Abell 21 • Sh2-274 • Medusa Planetary Nebula

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Abell 21 • Sh2-274 • Medusa Planetary Nebula

I tried capturing Abell 21 (Sh2-274) in the Spring on 2019. Typically Springs here in Michigan are pretty bad with clear skies and was only able to gather 12.8 hours of integration time between Ha and OIII back then. We had a very unusual March this year with a lot of clear nights and added on data to what a collected before. While I wanted to bring out more detail in the nebula itself, there was a lot of background nebula I wanted to pull out as well and see how far I can sharpen it.

Although Abell 21, or Sh2-274, has a large apparent diameter of 10 arcminutes, its surface brightness is so low, with features ranging from magnitude 16-25, that it was not discovered until 1955. It is a planetary nebula lying at a distance of 1,500 light-years in the constellation Gemini, which gives it an estimated diameter of 4 light-years. The parent star, now a white dwarf, is thought to be the deep 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 the mythical character Medusa, giving the nebula its popular name, the Medusa Nebula. The braided shell cradles a sphere of gas glowing a soft blue, largely due to emissions by OIII.

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Description: Front cover of Sky's Up Magazine January 2024

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