| Emission nebula | |
|---|---|
| H II region | |
 | |
| Observation data: J2000.0epoch | |
| Right ascension | 00h 52m 59.3s[1] |
| Declination | +56° 37′ 19″[1] |
| Distance | 9500[2] ly (2900 pc) |
| Apparent dimensions (V) | 35′ |
| Constellation | Cassiopeia |
| Physical characteristics | |
| Radius | 48 ly |
| Notable features | open clusterIC 1590, the multiple star B 1, and severalBok globules |
| Designations | IC 11, Sh2-184,[3]Sharpless 184,[1]LBN 616,LBN 123.17-06.28, Pacman Nebula |
| See also:Lists of nebulae | |
NGC 281,IC 11 orSh2-184 is a brightemission nebula and part of anH II region in the northern constellation ofCassiopeia and is part of theMilky Way'sPerseus Spiral Arm. This 20×30arcmin sized nebulosity is also associated withopen clusterIC 1590, severalBok globules and the multiple star, B 1. It collectively forms Sh2-184,[3] spanning over a larger area of 40 arcmin.[4] A recent distance from radioparallaxes of watermasers at 22GHz made during 2014 is estimated it lies2.82±0.20 kpc (9200 ly) from us.[5] Colloquially, NGC 281 is also known as thePacman Nebula for its resemblance to thevideo game character.
Edward Emerson Barnard discovered the nebula in August 1883, describing it as "a large faint nebula, very diffuse". Multiple star 'B 1' or β 1 was later discovered byS. W. Burnham, whose bright component is identified as the highly luminous O6 spectral class star, HD 5005 or HIP 4121. It consists of an 8th-magnitude primary with four companions at distances between 1.4 and 15.7arcsec. There has been no appreciable change in this quintuple system since the first measures were made in 1875.
The nebula region is visible in amateur telescopes from dark sky locations.In his bookDeep Sky Wonders,Walter Scott Houston describes the appearance of the nebula in small telescopes:[6]
