Exposures: 90 min Ha (3nm); 30 min each RGB for a total of 3 hrs
FOV =47.8 x 33.2 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. Until the early 1970s, the Medusa was thought to be a supernova remnant. With the computation of expansion velocities and the thermal character of its radio emission, Soviet astronomers in 1971 concluded that Abell 21 was most likely a planetary nebula.
1500 light years away and 4 ly across
Cropped slightly and reduced 60% from original
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