Medusa Nebula (A21, PK205+14.5)

Medusa Nebula
All Images
Copyright Steve Cannistra

Please click here for a larger image (65%).
Please click here for an inverted image (65%).

Size: About 10' (4 light years across)
RA: 07h 29m 31s
Dec: 13 degrees 13' 33"
Position Angle:  minus 50 degrees

The Medusa Nebula is a planetary nebula in Gemini.  It was discovered by Abell in 1955 and originally thought to be a supernova remant (SNR), although this was revised in the 1980s when it was recognized to be a very old planetary nebula.  It is interesting that another planetary, SH2-188, was also mistakenly thought to be a SNR, in part due to its asymmetric shape (most planetaries are symmetric).  I imaged SH2-188 in 2006 and provided some background information regarding planetaries in general, and SH2-188 in particular.  Please feel free to check it out, since this information also has relevance for understanding the Medusa Nebula.

I was surprised to see a very distinct, surrounding glow of faint Ha emission in this image, located just left of center.  In a manner similar to that of SH2-188, one gets the impression that the Medusa is coursing through the interstellar medium from left to right, with its trailing edge being dissipated over time.  This would explain why there is  hydrogen gas in its wake and would also explain why the tail end of the nebula is poorly defined compared to the leading edge.  Unlike SH2-188, however, I cannot find any documentation on the web to know whether my interpretation of this is correct.  The faint Ha region next to the Medusa can be easily seen in my inverted image.  It is poorly seen, or not seen at all, in most amateur images of this nebula on the internet.  Perhaps it has been processed out by those thinking that it represents uneven background!  A colleague of mine from Austria, Johannes Schedler, recognized this as a real finding and captured it in a wonderful wide field view of the Medusa, shown here.

The above image was taken through an Ha filter and will eventually be used in an Ha/OIII/RGB composite, once I have time to acquire the data.  The linear streak in the upper left hand corner is the track of asteroid Althaea.

Photographic Details:

Date:  February 16, 2008
Scope:  Takahashi FSQ106 at f5 on the Takahashi NJP Mount.
Autoguider:  SBIG ST-402 with e-finder.
Camera:  Apogee U32 -20C.

Astronomik 6nm Ha filter.
Exposures:  16 x 10'.  Total exposure 2.7 hours.
Conditions:  Temperature was approximately 23 degrees F over the course of the night.  Clouds moved in after midnight and spoiled the remaining subs.
Post-processing:  Calibrated, aligned, and Sigma Clip combined in Maxim, followed by DDP in ImagesPlus (IP).  Further processing in Photoshop CS (16 bit format).

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