The Phantom of the Opera Nebula, or Sh2-173, is an emission nebula in the constellation Cassiopeia. It is named for its resemblance to a face mask, which I hope is reasonably apparent to most viewers.

I was only able to find an Italian language Wikipedia page for this object, but Google's translation skills are pretty good.

This image is another narrowband capture, with RGB stars added for colour accuracy. In contrast with my previous narrowband images though, I have not attempted to produce a Hubble Palette image with this one. I have instead mapped the H-alpha signal to the red channel, the SII to green, and the almost non-existent OIII to the blue channel. The effect of this is to produce strong red colours where hydrogen dominates, and areas moving more towards orange where there is additional signal from sulphur. The data from oxygen really only serves to bring some smoothness to the background sky.

You can view this image in the WorldWideTelescope by clicking here.