| Emission nebula | |
|---|---|
| Planetary nebula | |
 Abell 31 as seen from the Mount Lemmon Observatory | |
| Observation data: J2000 epoch | |
| Right ascension | 08h 54m 11.4s |
| Declination | +08° 54′ 30″ |
| Constellation | Cancer |
| Physical characteristics | |
| Radius | 10 ly |
| Notable features | A very large and colorful PN |
| Designations | Sh2-290, PK 219.1+31.2, A 31, ARO 135 |
Abell 31 (also known as Sh2-290 or PK 219+31.1[1]) is an ancient planetary nebula in the constellation of Cancer. It is estimated to be about 2,000 light years away. Although it is one of the largest planetary nebulae in the sky, it is not very bright. The central star of the planetary nebula is a white dwarf with a spectral type of DAO.[2] The white dwarf is the dead remains of a star that existed but had died leaving behind Abell 31 and the white dwarf.[3]
Abell 31 is made mostly of hydrogen and oxygen gas with the red gas signifying hydrogen gas and the blue gas signifying the oxygen gas. The nebula has a blue central region being most of the nebula and a red ring around this blue region. The nebula due to its ancient age has its gas being dispersed into the interstellar medium.[4]
Some of the astronomical objects that exist around this nebula from our perspective include the Beehive Cluster (a cluster of about 1000 stars[5]), IC 523 (a galaxy), NGC 2731 (a spiral galaxy), M 67 star cluster (an old cluster of stars sometimes known as the King cobra cluster[6]) and many more.[7]