The Medusa Nebula (Abell 21)

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About this Image

The faint Medusa Nebula in Gemini, designated as Abell 21 or PK 205+14.1 is a very ancient planetary nebula in the constellation of Gemini. The inner bubble shows some hints of blueish structure, indicating that the central star (the blue one in the center) is still hot and makes the gas flouresce.
The distance to the Nebulae is estimated at 790 light years. North is right.

Below you find a 50/100% crop on the center of the above image.

clic for 100% size 1020 x 768 (140 kB)

Technical Details


410mm cassegrain in corrected prime focus at f/3

Mount MK-100 GEM
Camera SBIG STL-11000M at -30C, internal filter wheel
Filters Astronomik H-alpha (15 nm), green, blue
Date Mar 06, 2006.
Location Wildon/Austria
Sky Conditions mag 5 sky, Moon up, temperature -3 C,
Exposure Ha:G:B = 120:40:60 minutes (30-minute sub-exposures Ha, 10 min for G, B), all 1x1.
Processing Image aquisition, calibration and color combine in Maxim DL 4.11; curves, color balancing, light unsharp mask in Photoshop; Noise reduction by Neatimage