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Abell 21


Abell 21 - Medusa Nebula in Gemini

RA = 7 hrs 29 min; Dec = +13 deg 14 min

Date & Site:

Imaged on 01/04/14; Little Blair Valley, CA

Vey good seeing; Excellent transparency; temps in the low 30's


Telescope: TEC 140 f/7 refractor (fl 980mm)

Mount: Losmandy G-11 with Gemini
Camera: ST-10XME; CFW10 with Astrodon filters;

Hutech Off-Axis Guider


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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