Abell 31 (Sh2-290) – A Planetary Nebula in Cancer

Glowing red with ionized hydrogen gas and blue with ionized oxygen gas, Abell 31 is an old planetary nebula in the Cancer constellation roughly 2,000 light years from our solar system.

With a diameter of 22 light years, Abell 31 is one of the largest known planetary nebulas. Because it has expanded so much into the surrounding interstellar medium from its progenitor star, it has very low surface brightness.