IC 289
Planetary Nebula
aka PNG 138.8+02.8, PK 138+02.1, ARO 86
RA: 03h10m19.2s Dec: +61°19'01" (Cassiopeia)
Integrated Visual Magnitude: 12.3
Angular Diameter: 35"
Mean Surface Brightness: 19.8 Mag/arc-sec²
Distance 4200 ly

Minimum requirements to detect: 6-inch under dark skies


IC 289 is a pretty little planetary nebula in photographs and  large-aperture instruments.  Discovered by Swift in 1888, it lies just to the south of the 10th magnitude star BD + 60 0631, which makes it a fairly easy find.  At high magnification it appears to "flip" orientation!

IC 289 has been described as faint and homogeneous in an 8-inch.  A UHC or OIII filter helps make it more visible.  The UHC is recommended for scopes less than 14-inches, but the OIII will show more detail in larger instruments.  N.J. Martin described IC 289 as, "A nice, faint round planet like planetary nebula.  The uniform oval disc shows some irregularity in brightness but is not obviously brighter at the edge."

In my 18-inch f/4.5 IC 289 appeared as a small elongated hazy spot at 97x.  I noted that it was faint, but averted vision was not required to see it.  The OIII filter improves its visibility greatly.  At 250x it appeared elongated and diffuse, with a slight outer ring.  This planetary must be fainter than the reported magnitude of 12.3, perhaps more like 13.3, to account for the relatively low surface brightness.  The number given above of 19.8 mag/arc-sec²  seems much too bright.  I'd estimate it as more like 22 mag/arc-sec². 

My best view came at 430x with the OIII in place, where the light was spread out enough that it was nearly an averted vision object.  The outer ring was much more easily detected.  What really stood out at this magnification was a new sort of "blinking" phenomenon.  The planetary has a faint outer envelope which is round, or perhaps even aligned at a right angle to the elongated inner region.  This outer envelope only becomes apparent with averted vision.  As you switch from direct to averted vision the nebula appears to flip orientation!  The effect was as dramatic as it was unexpected.


The field in an 6-inch f/8 at 50x.  North is down and east is to the right.
Millennium Star Atlas Vol I Chart 45
Sky Atlas 2000 Chart 1
Uranometria 2000 Vol I Chart 18
Herald-Bobroff Astroatlas B-01 C-04

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