Abell 21
Abell 21 (also known as the Medusa Nebula) is a very old and large planetary nebula. It is estimated to be over 4 light-years across. The faint bubble seen overlapping the nebula in the upper left corner of the image is either a shell of gas blown off of the star before it became a planetary nebula, or the result of the nebula interacting with the interstellar gas surrounding the star.
| Observatory: | Kitt Peak National Observatory Kitt Peak, Arizona |
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| Telescope: | KPNO 4-Meter |
| Instrument: | Mosaic I |
| Astronomer: | T.A. Rector (University of Alaska Anchorage) and H. Schweiker (WIYN and NOAO/AURA/NSF) |
| Date of Observation: | 10-24-2008 |
| Filters and Assigned Colors: | Hydrogen-alpha (orange) and Oxygen [OIII] (blue) |
| Exposure Times: | 5x10min in each |
| Location of Image: | Gemini |
| Field of View: | 36.1 x 36.0 arcmin |
| Orientation: | North is right, East is up |
| Link to Larger Image | |
| Link to Full Resolution Image | |
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