Open Clusters in Cassiopeia

21 – 22 September 2020, 21:45 – 01:00

Conditions: Mild to begin with, but soon turning chilly. No wind. Condensation increasing over the course of the session.

Seeing: Average
Transparency: Poor

Again, with a couple of hours to spare before Mars reached a usable altitude, and the transparency no better than the previous night, I filled the time by touring some of Cassiopeia’s many open clusters.


M52, open cluster, Cassiopeia

133x. Rich, vaguely delta-shaped cluster with a bright star on the eastern corner.

Also of note: between 21:50 and 21:55 BST, while looking at this cluster I spotted an unusually slow-moving satellite of about 8th or 9th magnitude, winking into view every three seconds. It was travelling west to east, and passed just south of M52, taking about a minute to cross the field of view. Later, when I was back indoors, I used a quick back-of-the-envelope calculation to estimate it was on a 12-hour orbit. This puts it squarely in the Medium Earth Orbit (MEO) range; the first time (as far as I can remember) that I’ve observed one of these satellites.

NGC 7790, open cluster, Cassiopeia

133x. Compact cluster of about 20 faint stars with an underlying unresolved haze. Quite a nice view. In the same field of view to the NW was an even smaller triangular cluster of about 6 stars plus an unresolved haze – what I assume to be NGC 7788.

I looked (rather optimistically, it has to be said) for the galaxy IC 10, but couldn’t see it. However I did spot a very close double star nearby, just to the north.

NGC 129, open cluster, Cassiopeia

133x. Large, loose cluster with a mixture of bright and faint stars. No underlying haze that I could see.

NGC 225, open cluster, Cassiopeia

133x. Large cluster of about 20 to 30 similarly bright stars.

King 14, open cluster, Cassiopeia

133x. Faint stars plus haze in a rich star field, just NW of 15 (Kappa) Cas. It's a nice field in the Nagler, but the cluster doesn’t really jump out.

NGC 7789, open cluster, Cassiopeia

133x. Not so well resolved tonight as on previous occasions, but still wonderfully rich. Looked like a hazy “swarm” of stars.

NGC 559 (Caldwell 8), open cluster, Cassiopeia

133x. Small, hazy, rectangular cluster with bright stars on each corner; the brightest stars on the eastern side formed a triangle. More stars popped out with averted vision.

NGC 663 (Caldwell 10), open cluster, Cassiopeia

133x. Rich, large, lots of bright stars, plus that distinctive horseshoe shape. Always impressive.

NGC 659, open cluster, Cassiopeia

133x. Small, arrowhead-shaped cluster near NGC 663. Fainter stars of similar brightness plus two bright ones (are these foreground stars?).

IC 1747, planetary nebula, Cassiopeia

I added the 2.5x Powermate to boost the magnification to 333x, but before heading to Mars, I paid a return visit to this little planetary nebula. There wasn’t much to see other than a faint little disc – but at least it was an obvious disc as opposed to a bloated star. With averted vision it seemed slightly brighter on the western side, but this feature (if real) was very subtle.

Mars: 333x. The seeing wasn’t quite as good tonight as it had been over the weekend, but the Sinus Sabaeus region was still showing well, with just a hint of Syrtis Major on the evening limb.