Project Description

Medusa Nebula/Abell 21

Official designation for Medusa Nebula/Abell 21 planetary nebula is PK205+14.1. It is also listed as Sharpless 2-274. Although initially thought to be a supernova remnant, the Medusa is a large PN in Gemini about 1,500 light years distant and 4 light years across. It is considered to be an old planetary nebula. North is to the upper left. The brighter portion toward the SE gives it a crescent moon appearance. The high contrast of the narrowband filters brings out additional, faint shock front structures toward the NW, showing a more oval shape to the object. There are faint areas of nebulosity outside the main structure.

These data were taken with Astrodon 3nm FWHM H-a, OIII and NII narrowband filters. A 3 nm bandwidth begins to separate the (spectrally) adjacent H-a and NII emission lines. The colors were assigned similar to the Hubble narrowband palette in order of increasing wavelength, with B = OIII, G = H-a and R = NII. RGB data were added for star colors.

Constellation: Gemini
Ra: 07h 29m
Dec: +13d 15m
Distance: 1,500 light years
North: Upper left
Image Credit: Don Goldman, PhD

Exposure: 17 hrs Total: 14 hrs Narrowband, 3 hrs RGB
Telescope: RCOS 16
Mount: Software Bisque Paramount ME
Oag: Astrodon MonsterMOAG
Acquisition: CCD AutoPilot4
Calibration: CCDStack2
Observatory Site: Sierra-Remote Observatories, Shaver Lake, CA
Camera: Apogee U16M
Filters: Astrodon 3nm H-a, NII, OIII, Gen 2 RGB
Guider: SBIG ST-402
Camera Operation: MaximDL4.62
Processing: Photoshop CS3
Image Date: 01/06/2010

View more of Don Goldman’s images at