This is an image of the Medulla Nebula in hydrogen alpha. The Medusa Nebula is also known as Abell 85, CTB 1 and LBN 576. It’s a supernova remnant in Cassiopeia. The Abell designation was made by mistake. Abell put it in his catalog of planetary nebulae. However, this turned out to be a supernova remnant.

According to Wikipedia, there sin’t much consensus about the distance. Some studies place it at 6,500 light years and others as much as 14,500 light years. Its age has been estimate to be about 10,000 years or as much as 16,000. So, there appears to be a lot left to learn about it.

I can say for certainty that this is a very faint nebula. It was originally intended to be an HOO image (hydrogen in red and oxygen in blue and green). We captured 8 hours of H and 16 of O but the O was still too faint. It turned out to be impossible to reveal the O without also revealing the limits of the sensor. So, rather than spend even more time capturing at least 16 hours (and likely a lot more) of OIII, I opted to process this as a monochrome, hydrogen-alpha-only image.

The H signal was plenty strong and was actually fairly straightforward to process. You can see the nebula against a backdrop of galactic hydrogen gas.

For all the technical details, see astrobin.