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Saturday, November 1, 2008

Cetus on a crystal clear night

Friday night was crystal clear, so despite being tired (eyes especially) and having some back pain, I just had to get out observing. So I went to my favorite close-in spot about an hour away in the foothills of the Blue Ridge Mountains, where the limiting magnitude is about 5.8. A raccoon and I were the only ones out there, not counting the unseen multitudes that slither and crawl (no, there were no political campaigners out there!).

With transparency about 9/10 but seeing only 5-3/10 (progressively worse) it was a good night for faint galaxies. What space is more fertile than Cetus for that? To me Cetus forms the shape of Aladdin's Lamp with a long handle. So I spent some time inside the lamp, around the spout toward the west. All observations were made with my 10-inch Hardin dobsonian using my Baader Hyperion zoom eyepiece and a barlow (sometimes adding an NPB filter) only. This gives me a range from 52x to 312x. About 75% of my observations take place at 52x to 156x, that is, without using the barlow.

I know I said galaxies, but planetary nebula NGC 246 was my first target. It's a whopping 245" in diameter--considering all the tiny compact planetaries that abound, that's on the "whopping" end of things--and magnitude 10.9, according to the Historically Corrected NGC. There's a narrow triangle of two 12th mag stars and one 13th mag star that falls within the nebula, although the apex star is just outside the edge--in the scope it looks like it's right on the edge. One of the stars forming the base is the central star. This is the brightest of a type called a PG 1159 star, which is in a hydrogen-deficient transitional phase toward becoming a hot white dwarf. This star varies in brightness slightly (i.e., get out your photometric device if you want to detect it) in a matter of hours. The nebula responds well to my DGM NPB filter (narrowband nebula filter), making the outline of the disk more distinct. NGC 246 is considered a "high excitation" planetary nebula, so be prepared to get excited if you observe it!

But we're talking primarily galaxies last night, and here's a rundown:

NGC 255: 11.7 mag. Not far from the planetary in Cetus, it's a round smudge in 156x, just slightly brighter in the center. Low surface brightness- looks a lot dimmer than 11.7. We're looking at a face on barred spiral with this one.

MCG-2-3-19: I'll usually stake out a spot in the sky when galaxy hunting and check out anything in the area. This one is 13.9 mag and about all I could make out was its lenticular shape in higher power. A 13.2 mag geosynchronous (or nearly so) satellite passed through the field. I haven't picked up one of those in a while, but when observing at this altitude in the southern sky, it's not as uncommon as you might think, being as there's so much stuff in orbit now. This was drifting slightly north and varying slightly in brightness, so it may be old or off-station. Geosynchs generally stay put in your field of view while the stars around it drift to the west. It's a bit of an eerie sensation when you first pick one up.

NGC 283: 13.6 mag, which I found to be the most difficult object of the night so far. Just a hint of it, barely confirmable.

NGC 286: 14.1 mag. Small and compact. I just got glimpses of it.

IC 51 (ARP 230): 13.0 mag. The DSS image I have looks like it's a polar ring galaxy, and sniffing around the Internet bears that out, not that I could tell in the scope, though it appeared elongated NE-SW at first. Formed from two colliding galaxies. There's a 15.2 mag star visible just off to the SW.

NGC 210: 11.1 mag. Appears somewhat round with a well condensed stellar core, brightness drops off pretty dramatically outisde the core area, levels off for a while, then piddles out with ragged edges. The linked image mistakenly places it in Fornax.

NGC 151: 11.6 mag. Soft glow with soft edges. Oriented ENE-WSW, small brighter core, nearly stellar. Oval glow around that. I couldn't make out the spiral arm that curls around the south to a 13.4 mag star to the east that's visible in images. Brightness drops off a little more abruptly on the NE side of the core.

NGC 157: 10.4 mag. Looks a bit similar to NGC 151, though a bit fatter. Appears to be a faint star off the NE end. I can't see the dimmer one next to it that's visible in images, though I thought I might have gotten occasional glimpses of it. A wispy arm extends out that way on the southern side, just discernible in higher power. This one is tantalizingly close to showing a lot of detail in the 10-inch. I'm just picking up a little of it. Center gets a little brighter but only hints of a distinct core visible, though there seems to be a spine of brightness running through the center. It's funny how these objects look like nothing more than little fuzzballs at first, but then start showing the faintest, subtlest details if you look long enough.

MCG-1-2-34: 12.8 mag. Less than a degree away from NGC 157. Dimmer than the mag suggests. Elongated a little E-W. A little fluff of cotton, ovoid and a little hairy around the edges.

Okay, so at this point I took a coffee/warm up break and then began straying a bit farther for other interesting objects.

IC 298 (ARP 147): 15.0 mag. I had to go for this pair of galaxies because the Hubble Space Telescope is working again and this is the first published image since the fix. Only the faintest glimmer in the 10-inch, however, though that's probably a combination of the galaxies and some nearby stars. They're in the eastern part of Cetus, below the long "handle" of the lamp.

Baade 1: 13.9 mag. I've observed this planetary nebula before, but didn't have my NPB filter at the time so I thought I'd try for it again. Just the faintest spot visible about 5% of the time with the filter on and only when I'm actively zooming slowly between about 125x and 150x--one of the reasons I really like the zoom eyepiece. Could also spot it at about 225x without active zooming. Images of this one are hard to come by--hint to any advanced imagers out there! Scroll about 3/4 down the linked page for a rare shot.

Abell 12: 13.9 mag planetary nebula. This one is right next to 4.1 mag Mu (61) Orionis, and is pretty much lost in the star's glow. It's just on the NW side of the star. I thought I got a flash or two of it with the NPB filter on, but couldn't confirm. The seeing had gotten pretty bad by this point, too. This is one I'll have to try for again, especially right after I clean the scope's mirror.

NGC 2022: 11.6 mag planetary nebula in northern Orion. Shows up well in 300x with the NPB filter. Disk with slightly darker center and a fairly sharp edge. The southern edge is the brightest. Slightly elongated N-S. Also does well without any filter. Couldn't see the central star, which is 15.9 blue mag.

Abell 11: 17.1 mag planetary nebula in Orion. No expectation to have seen it in the 10-inch. I figured I'd try anyway, but no luck.

Abell 10: 15.2 mag planetary nebula in Orion. Best view in 200x with the NPB filter. A small round patch, uniformly bright across the disk. Again, the filter helps to define the disk better.

It was about 3 a.m. at that point, so I made the usual pilgrimage over to M42, then gawked at open cluster M35 and nearby NGC 2158 before packing it in.

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