This faint
supernova remnant (SNR) is located 7000 light years away (2014 estimate) in the constellation of Monoceros at a declination of +6 degrees. It spans about 1 degree in our apparent view and has a diameter of about 120 light years. Unlike many popular SNR, this one does not have a name or common designation and is simply referenced by its galactic coordinates at 206.9° galactic longitude and 2.3° galactic latitude.
At 120 light years in diameter, this SNR is about the same size as the
Cygnus Loop SNR. The
Sh2-240 SNR is a bit bigger at 150 light years, while the
Vela SNR is a bit smaller at 100 light years.
Like the
Vela SNR, this SNR is comprised primarily of OIII signal. Like the
Sh2-240 SNR, this SNR is not spherical in shape but is somewhat squashed, with the long axis running from lower left to upper right. I think that irregular density in the surrounding ISM could be responsible for the asymmetric shape. I have included a starless image version (Revision F) which more clearly shows the SNR structure.
The red nebulae you see in the image is the eastern part of the Monoceros Loop SNR.
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