| Emission nebula | |
|---|---|
| Planetary nebula | |
 Abell 31 as seen from theMount Lemmon Observatory | |
| Observation data:J2000epoch | |
| Right ascension | 08h 54m 11.4s |
| Declination | +08° 54′ 30″ |
| Apparent magnitude (V) | 15.5[1] |
| Apparent dimensions (V) | 16.2′[1] |
| 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 |
| See also:Lists of nebulae | |
Abell 31 (also known asSh2-290 orPK 219+31.1[2]) is an ancientplanetary nebula in the constellation ofCancer. It is estimated to be about 2,000light years away. The centralwhite dwarf has aspectral type of DAO.[3]
Abell 31 is mainly composed ofhydrogen andoxygen gas.[4] The blue oxygen occupies the central region and makes up the bulk of the nebula, while the red hydrogen makes a ring at the nebula's edge. This object is very old, and consequently, it is very large and dim (specifically, it has a lowsurface brightness), and its gas is dispersing into theinterstellar medium.[5]
Some astronomical objects that appear nearby from our perspective include star clustersMessier 44 and67, and galaxiesNGC 2731 andIC 523, among many others.[6]
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