Abell 12 and μ Orionis

Object Description

Abell 12
Abell 12: Planetary nebula near star μ Orionis; 500 mm Cassegrain 3625 mm f/7.2 + SBIG STL11K; 21+10+10+10 min LRGB; Bernese Highlands; © 2011 Radek Chromik

In 1955, George Ogden Abell published a list of planetary nebulae that were discovered on the photographic plates of the Palomar Observatory Sky Survey. Most of them are significantly larger than Abell 12 and usually have a low surface brightness, so this object is an exception among the Abell PN.

There are contradicting brightness data for the central star; Abell himself mentions 19.1 mag, the Strasbourg ESO catalog [141] gives a Johnson's B filter magnitude of 19.7 mag, while the “Deep Sky Field Guide” [22] lists 14.9 mag. There are also different data on the size: The PK67 and the Strasbourg-ESO have an optical diameter of 37", while the field guide only allows the object to be 18". Radio measurements showed a diameter of 35". Distance measurements vary from 1.7 to 2.7 kpc. [141]

— 1999, Frank H. Leiter

Further infos at CDS: PN A66 12

«Strasbourg-ESO Catalogue of Galactic Planetary Nebulae» Acker et al., 1992 [141]
DesignationsPN G198.6-06.3: A 12, PK 198-06.1, ARO 220
Right Ascension (J2000.0)6h 02m 23s
Declination (J2000.0)9° 39' 03"
Dimensions 37." (optical), 35." (radio)
C-Star DesignationsAG82 56
C-Star Magnitude19.7 mag (B filter)
DiscovererABELL 1964

Finder Chart

Finding Abell 12 is fairly easy, as it is just under an arc minute west-northwest of the star μ Orionis. The latter is visible to the naked eye (4.1 mag). Whether the PN is then also visible in the eyepiece is a question of the aperture and contrast performance of the telescope, as well as the quality of the sky. The constellation Orion is best observed from October to February.

Chart Abell 12
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

Visual Observation

Abell 12 is actually easy catch - if you follow the object data in the Deep Sky Field Guide. Since the planetary nebula is very close to μ Orionis, the observer can find it easily, but has a very bright star in the field of view, which makes sighting considerably more difficult. For this reason, there are so far only very few photos of the object.

200 mm aperture: Despite the obstruction by the bright star, Abell 12 is detectable under ~ 6.0 mag sky with an 8" aperture; even without a nebula filter. A very good contrast performance of the optics is important. In addition, the spikes of the secondary mirror holder should not run over the nebula in a Newton. An [OIII] filter enhances observation. — 1999, Frank H. Leiter

320 mm aperture: The PN lives up to its reputation as an object that can only be seen with high contrast performance. With a somewhat hazy, slightly turbulent sky, with the crescent of the waxing moon and slightly dusty optics, the nebula is not visible in the halo of the bright star μ Orionis without filter. With an O-III filter, it gave now and then a very dim glimpse. — 5. 2. 2022, Ibergeregg, Stefans 320 mm f/5 Dobsonian, Bernd Nies

400 mm aperture: At 145x magnification, the nebula is easily visible with and without an [OIII] filter. It appears as an almost uniformly round surface. From a magnification of 200x, the surface appears structured; it is helpful if the star μ Orionis can be moved out of the field of view. A ring fragment on the side facing away from the star is noticeable. There is a faint star at its southern end. The central star could not yet be visually detected. — 1999, Frank H. Leiter


22«The Deep Sky Field Guide to Uranometria 2000.0» by Murray Cragin, James Lucik and Barry Rappaport; Willmann-Bell, Inc.; ISBN 0-943396-38-7
141Strasbourg-ESO Catalogue of Galactic Planetary Nebulae; A. Acker, F. Ochsenbein, B. Stenholm, R. Tylenda, J. Marcout, C. Schohn; European Southern Observatory; ISBN 3-923524-41-2 (1992); cdsarc.unistra.fr/viz-bin/cat/V/84 (2021-02-18)
149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form