Cassiopeia
Planetary Nebula
RA: 01 30 30
Dec: +58 23 30

Sh2_188_DSS.JPG

DSS image of Simeis 22 / Sh2-188

I was inspired after reading Scott Harrington’s article in the December 2022 issue of Sky & Telescope. He wrote about planetary nebulae in Cassiopeia, many of which I wasn’t familiar with, so I put my copy of the magazine in my observing bag so I’d be ready for the next clear night. Unfortunately, I’ve only had one night since then with a good enough sky to give some of these nebulae a shot. Happily, Simeis 22 was surprisingly easy to see from my semi-dark backyard.

To find out more about this PN, I refer you to either Scott’s excellent article or this page (https://www.deepskycorner.ch/obj/sim22.en.php). I won’t rehash all that here, and will concentrate on sharing my observing experience of this intriguing object.

Located about 2 degrees south of magnitude 2.7 Delta Cass (Ruchbah) and about 1.5 degrees east of the popular open cluster NGC 457, Simeis 22 is relatively easy to find in even a moderately light polluted sky. Easy enough that I found it on my first try, which isn’t always the case.

It was immediately visible in a low power eyepiece + OIII filter, which framed it quite nicely. My notes:

“This is a pleasant surprise – I can see an arc of nebulosity. Its edges are indefinite and I can’t tell if I’m really seeing an arc or a straight segment of the nebulosity. A faint stream of stars intersects its western end, giving the impression of the nebula curving along with it. 113x, OIII filter, 20.24 SQM (30-inch f/2.7)”

Sh2-188_stars_adjusted.jpg Sh2-188_stars_adjusted_invert.jpg

North is to the upper right in my sketch, and you can match the small curl of stars near the western end of the nebulous arc to the DSS image.

Simeis 22 was invisible without the OIII filter, but I have the feeling it could be seen in a darker sky, and that the strongly curving arc would be more pronounced with an OIII then too. Time will tell as I definitely plan to come back to this wonderful object.

In the meantime - well, you know!