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Abell 21



Abell 21: Medusa Nebula in Gemini

RA = 7 hrs 29 min; Dec = 13 deg 15 min

Date & Site:
Imaged on 12/22 - 12/23/11; Running Man Observatory, Carlsbad, CA

Telescope: Vixen 200mm Newtonian (800mm FL F4.0)
Mount: Losmandy G-11 with Gemini
Camera: ST-10XME; CFW10 with Astrodon filters; Internal autoguiding


Exposures: Ha=2.25 hrs; OIII=1.5 hrs

FOV = 32 x 30 arc minutes

Commonly known as the Medusa Nebula The braided serpentine filaments of glowing gas suggests the serpent hair of Medusa of ancient Greek Mythology. Abell 21 is a very ancient planetary nebula, an expanding shell of gas surrounding a dying star, formed from matter ejected from the star's outer layers; the gas is ionized by the remaining hot stellar core, emitting light in the process

Color mapped by assigning Ha to orange and OIII to blue

1500 light years away; It is estimated to be over 4 light-years across

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