This large dim supernova remnant (SNR) is located 7200 light years away in the constellation of Cassiopeia at a declination of +63 degrees. It spans about 2 degrees in our apparent view. This corresponds to a diameter of 260 light years.
SNR G132.6+01.5, also known as HB3, is one of the largest Galactic SNRs observed to date. It is estimated to be 50,000 years old and is located just north and west of the Fishhead Nebula, seen in the lower left of the image. The Fishhead is just north and west of the Heart Nebula.
In 2022,
@Kurt Zeppetello posted an
excellent image and writeup on this object. I enjoyed his description so much that I am quoted his words here:
"The framing is not a mistake, it is centered on HB3. HB3 is a Supernova Remnant (SNR) first cataloged by a radio astronomer and imaged optically in February of 2022 by a research group (article from the Royal Astronomical Society,
https://arxiv.org/abs/2202.07749v1). I first found out about this object from Göran Nilsson who produces incredible images using his dual RASA rig from Värmland, Sweden (
https://www.astrobin.com/96arhu/B/). According to the authors of the article, the SNR formed in a wind bubble cavity created by the progenitor star. The estimated mass of this Wolf-Rayet star is 34 solar masses."
An image of the SNR from the paper above is shown below:
I imaged the SNR using my typical approach - an HOO palette with RGB stars. But I have since learned that there is enough SII here to make including it worthwhile.
The fun little blue PN in the upper left of the image at RA 022045 & Dec 631135 is PN G132.8+2, seen below at a longer focal length:
PN G132.8+2.0 
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