Abell 31 (AKA Sh2-290) is a planetary nebula in Cancer. It’s a relatively faint nebula, but not so faint that it is hard to image, at least from a dark site. The middle of the nebula is primarily oxygen surrounded by a ring of hydrogen. There is a faint background glow of hydrogen that tints the background red.

According to Wikipedia, the nebula is about 2,000 light years away and is very old. However, the article does not say exactly how “ancient” it is. Because it has such low surface brightness, it is probably only accessible to imaging and not to visual observers (unless they have a very large telescope in a very dark sky).

This image is HOO (hydrogen in red and oxygen in blue and green). This approximates the natural color of the nebula. The stars were imaged in RGB filters and so are natural color.

This is 11h 50m of HOO data (plus additional time for the RGB stars). If you want the technical details, see astrobin.