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Sunday, March 29, 2009

A cold winter finally nears an end

I did finally get out observing again on Friday, March 20 for a few hours up in the Blue Ridge foothills. Although it was clear, the transparency (and seeing) were disappointing and the temperature hovered around freezing with a lower wind chill. But it was nice to brush the cobwebs out of the scope tube and see a few interesting objects. No one else from the club came out despite my post to the mailing list that I was heading out. Observations were made with my 10-inch dob, Baader Hyperion zoom eyepiece with 2x barlow and DGM Narrow Pass Band filter, where applicable. That's my basic setup that works wonderfully for everything I observe. I like to keep it simple.

I had picked out a few objects in Monoceros for the last time I thought I was heading out but didn't, so I started with those.

NGC 2324 is an 8.4 mag open cluster also cataloged as Collinder 125 and Melotte 59. Per Collinder was a Swedish astronomer who also wrote a notable book on the history of marine navigation and who died in 1975. Philibert Jacques Melotte was a British astronomer of Belgian parents. He discovered the little known 50 km wide moon of Jupiter named Pasiphae in 1908 and died the same year I was born- 1961. NGC 2324 is not too far from Delta Monocerotis and pretty close to the Canis Minor border. It wasn't really obvious in the 10-inch at lower power. Though I could resolve most of it at 60x, the handful of brightest stars are around 11th mag and the rest- about 60 or so visible- are dimmer. Rich but faint. It has a ragged oval shape reminiscent of the Crab Nebula. There's a dim little double star of about 12.5 and 13 mag down off the SW edge, outside of the cluster, with a position angle of about 200 or so on the secondary. The cluster got better as I went up in power until about 180x at which point the seeing, which wasn't better than 6/10 at any time, limited the resolution. This is a relatively young, metal-poor, and distant cluster.

Nearby is the 11.6 mag planetary nebula NGC 2346. Or so I thought, anyway. I had never observed this one, and it turns out I left out a "-" sign in the McNeil planetary file, so I had it plotted about 1.5 degrees off. I've corrected the position in the file I have on the Astronomerica site. You can change yours just by adding a "-" before the declination, making sure the columns after it line up by removing a space. Anyway, once I did find it, it was fairly unmistakable as a planetary with an 11.5 mag central star surrounded by a diffuse glow. Nothing like the images that give rise to its nickname the "Hourglass" or the "Butterfly." In fact, the slightly oval-shaped inner glow was all that was visible, oriented NNW-SSE, which is perpendicular to the "wings" or glass bulbs of the hourglass that are visible in images. Still it's a pretty nice one, especially if you take a filter to dim down the central star and get a better look at the glow. You'll need to start at about 150x and go up from there to see any shape to it. There's a 13.5 mag star just off the eastern edge of it, and it appears that the glow on that side has a slightly sharper, straighter drop off. This planetary is somewhat unique in that its central star is actually binary, with the pair of stars locked in a tight 16-day orbit. This situation is probably what caused the butterfly "wings" effect. The planetary is about 2,000 light years away and about 1/3 of a light year across.

I took a brief look at Saturn, but the seeing really didn't favor planetary observing tonight. The rings are a bit thicker than when I observed them last, two months ago, and I could detect a little tilt to them already.

With a cold breeze picking up, I decided to face the other direction, and turned to IC 3568, a 12th mag planetary in Camelopardalis. There's a bright double star nearby, Struve 1694 (32 Cam, WDS 8682), 5.3 and 5.8 mag, which is where I started from. It's a nice wide one, and sometimes included in lists of the best bright doubles in the sky. The separation is about 20" or so and it's like a pair of white eyes peering back from deep space. There's another dimmer double not far from it- Struve 1720, but at 9th mag and with a separation less than 2", I didn't bother with it, given the relatively poor seeing.

Onward to the planetary. This one showed two concentric shells, not well defined, with the dimmer outer shell extending about halfway out to a 14.3 mag star about 50" to the west. I don't usually see much blue in planetaries anymore, but this one had a hint of it when I first caught it in low power. I used the NPB filter to dim down the central star to get a better look at the nebulosity, though it doesn't do a whole lot to bring that out. IC 3568 was discovered by Robert Grant Aitken, his only IC discovery, using the Lick Observatory 12-inch Clark refractor in 1900. The planetary was misclassified as galaxy UGC 7731 in the Uppsala General Catalog, and it shows that designation along with the IC number on my charting software. So don't go looking for the galaxy!

UGC 7410, however, is a real galaxy of 14.2 mag, less than half a degree to the WNW, but I couldn't spot it. Here's an image from the Aladin Previewer that might help you to try to spot it yourself (north up, west to the right, field is 12' wide, bright stars are 9.3 and 9.0 mag):

UGC 7410

So I decided to go for a few galaxies not quite midway between Alpha Draconis and Mizar and Alcor, the "horse and rider" in the handle of the Big Dipper. NGC 5308 is 11.7 mag. It was an easy pickup in 60x, with a stellar core and nice thin arms- clearly a fine edge-on. The linked SDSS image shows it having thicker, fuzzier arms, but in the scope they look quite thin. If you look at the image you'll see a couple of faint galaxies close in, with a guide star near each of them. I tried to locate the galaxies, and although I could make out both guide stars, I couldn't pick up the galaxies. I'll bet a darker sky might give them up.

A brighter neighbor to NGC 5308 is NGC 5322 at 10.1 mag. It's about 49" away to the SSE. This is an elliptical, which normally doesn't excite me much. See if you can pick out the star just south of the nucleus. The nucleus itself appeared not quite stellar to me, although that may have been a result of the soft seeing. In the linked SDSS image the glow is much more extensive than I could see in the scope. It's really interesting to compare your view to images, so you see how much larger these objects really are! For example, the star south of the nucleus is almost lost in the glow of the nucleus in the image, but in my scope it was just inside the galaxy's glow. The stars to the east and west of the nucleus are only about halfway out to the edge of the glow in the image but well outside the glow in my scope. These stars are also nowhere near as prominent in the scope as the star just south of the nucleus.

After a break to warm up in the car, I took a look at Mizar and Alcor. I sometimes forget what a nice system that is- good for showing off in the scope at public star parties because a lot of people are familiar with it only as a naked eye double. NGC 5204 is an 11.3 mag galaxy about 3.5 degrees to the NNE. It's dimmer than I thought it would be, but I could still pick it up easily in low power. It has the look of a dwarf galaxy, with no clearly defined nucleus and a diffuse shape with hints of subtle texture in higher powers. It is, in fact, classified as a "magellanic spiral," halfway between a bright spiral and a dwarf galaxy, a classification introduced by Gerard de Vaucouleurs in his de Vaucouleurs modified Hubble sequence. He was also co-author of the Third Reference Catalog of Bright Galaxies (RC3). NGC 5204 is home to an ultraluminous X-ray source that has been studied with the Chandra X-ray Observatory and the Hubble Space Telescope.

A quick look at M101, which wasn't too great with the transparency having steadily degraded throughout the night, and with Comet Lulin behind a tree at that point, I packed it in around 1:30 a.m.