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Thursday, November 27, 2008

Casting around in Cassiopeia

I was able to get back out to my site in the Blue Ridge foothills last night (5.8 limiting mag). Owing to a partly to mostly cloudy sky, I had to confine my observations to the northern part, with increasingly frequent breaks for clouds. There were a few objects in Cassiopeia I wanted to try for. I had my usual scope, a 10-inch dob.

NGC 457, the "Owl" or "E.T." cluster, was a nice starting point. This is a bright open cluster that I can see in the finderscope. A good one for beginners and veterans alike. Fifth mag Phi is the brighter "eye" star, which looked yellow to me this time, but is actually white.

NGC 436 is another open cluster nearby. Just go below the "feet" of NGC 457 about 2/3 degree. It's a small, compact cluster. I found it to be best at around 150x in the 10-inch. Using averted vision really brings out the richness of the cluster, which I'd guess has about 50 stars visible in this scope, most of them quite faint. I prefer the rich faint clusters to the bright, scattered ones.

Sharpless 2-188 is an ancient planetary nebula not far from the two clusters. This large, crescent-shaped nebula is easily mistaken for the Medusa Nebula (Abell 21) in Gemini. Too bad it's not as easy to see in the scope! I tried, with and without the nebula filter, but couldn't get any glimpse at all of it. There are some faint stars in its location, but that's all I saw. I'm wondering if the transparency just wasn't good enough at the time, so I'll have to try again on a different night, perhaps from a darker site.

IC 10 is a dwarf irregular galaxy in the Local Group toward the western end of Cassiopeia.It's the nearest starburst galaxy to the Milky Way. It was not an easy observation, just a small, faint, inconspicuous patch around a 12th mag star. It's just northwest of a triangle of 10-11 mag stars. There's a dimmer star very close to the east, a pair to the north a little farther out, and one to the northwest about the same distance as the pair to the north. All of these appear to be superimposed on the galaxy. Had to use the barlow to get a big enough image scale. Try this for a challenge with a 6 or 8-inch from a dark sky.

NGC 129 is another open cluster (this is Cassiopeia after all), located about 1-1/2 degrees northeast of IC 10. It's rich, but large and scattered. Most of the brighter stars congregate toward a 6th mag star to the south, with the rest scattered about in other directions. My program says the 6th mag star is supposed to be a double with a 9th mag companion to the west, but I couldn't see it. The seeing was only about 5/10 at the time, however. Berkeley 2 is a tiny cluster nearby (shown in the linked image), but I didn't have a position on it, so I didn't locate it in the scope.

NGC 103 was perhaps the highlight of an abbreviated observing session for me (abbreviated by the clouds). At first I thought it was composed of several loose clusters forming one larger grouping, but then realized the cluster is really the most condensed of these smaller clusters. It's an odd one, a very thin, small grouping pointing to the southwest with a curved tail on one side. The brightest star in the wider base of it is only 11th mag. I couldn't resolve most of its members, but it's still a cool little cluster. Would probably be best on a night of good seeing with about 200x. A good target for astro imagers, as there aren't many images of this one around.

I finished up the night with two goose eggs- no luck seeing either planetary nebulas PK 136+5.1 or Abell 6. Granted, they were both long shots, but I like to finish with something nice. However the clouds had taken over before I could get a filter on the Abell 6 field, so I packed up. Of course, once I had packed up, it cleared beautifully, but I needed to allow for the drive home, so I had to leave. Ain't that the way it often goes...