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-secē
seems much too bright. I'd estimate it as more like 22 mag/arc-secē.
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. |