by Peter Chapin
Tonight was a meeting of the VTC Astronomy Club. Rob, Ed, and I attended. We spent some time on club business (such as the budget) and then we reviewed the club's equipment. I'm impressed by the club's inventory and look forward to taking advantage of some of the club's equipment in the months ahead.
Since the sky was good we took out the club's 8" Dobsonian along with two pairs of 10x50 binoculars. We observed from the entrance to the VTC orchard just across from the dorms (not the lower entrance off the South Randolph Road). The observations that follow, unless otherwise noted, were all made with the 8" Dob using a 25mm plossel eyepiece (48x). In some cases we also used a 9mm eyepiece (133x). The Dob had a f.l. of 1200mm and a speed of f/6).
The sky was clear and reasonably dark. The moon had largely set by the time we got outside but the lights from VTC did cause noticable light pollution at our observing site. Nevertheless the trees did offer some protection and the limiting magnitude was >5 based on the naked eye observability of certain stars in Cyg. There was significant degradation of the sky conditions near the horizon. (A formal sky conditions report is at the end of this write-up).
We looked at several deep sky objects. I did not record our observations formally so the description that follows is from memory (write-up about 24 hours afterwards).
M31, M32, NGC-205 (And). We first put the 'scope on the Andromeda Galaxy. The view was most impressive. M31 was very bright, of course. M32 appeared as a large bright fuzzy star. It looked very circular. NGC-205 was fainter but still easily seen. The oblong shape of NGC-205 was clear. We were able to readily get the core of M31 in the same field of view as NGC-205 resulting in a most interesting view. I spent a little time scanning for some of the brighter features in M31's outer arms but I didn't see anything obvious. I'm not sure how large a scope is necessary to observe those features. It would probably have also helped if I had known better where to look.
NGC-7789 (Cas). This has always been one of my favorite clusters and I looked forward to seeing it in the Dob. Unlike the view in my 75mm, the cluster appeared fully (or almost fully) resolved. It was quite rich and the "dark lane" that I mentioned in previous observations was plainly visible. To be honest I almost prefer the partially resolved look that I'm used to. The Dob makes the cluster seem less "mysterious" somehow.
M2 (Aqr). This globular cluster was quite interesting in the Dob. It was bright and obvious but did not show any real signs of resolving using the 25mm eyepiece. However, in the 9mm I was able to make out a few member stars; the cluster had a generally granular appearance. Altogether a nice object.
M15 (Peg). This globular cluster also gave an impressive view. It seemed easier to resolve. Some stars were visible with the 25mm and the 9mm showed many. The cluster looked like a snowball in space.
M71 (Sge). I was most impressed with this object. M71 is in a limbo between open clusters and globular clusters and it made a good showing in the Dob. The rich Milky Way field enhanced the view yet despite that the cluster stood out clearly from the Milky Way background. It was only partially resolved. Although there were many member starts visible, the core of the cluster remained a foggy mist.
M57 (Lyr). The Ring Nebula. The Dob showed the doughnut shape clearly (especially with averted vision). The best view was with the 9mm. We noticed that the ring was not perfectly circular but rather somewhat oblong. A small star was clearly visible just outside the ring. I looked for the central star but saw nothing (I wasn't expecting to).
M27 (Vul). The Dumbell Nebula. Amazingly bright in the Dob. We were able to make out a "ragged" edge to the nebula although the central portions of the object seemed relatively featureless.
M33 (Tri). This face-on galaxy was surprisingly difficult to see in the Dob. Although it showed up easily enough, it was diffuse and less interesting than I had hoped. The low altitude didn't help; M33 was difficult to make out in the binoculars tonight. I look forward to studying this object under more favorable skys later in the season.
NGC-884, NGC-869 (Per). The double cluster. A beautiful view in the Dob! Both clusters fit comfortably in the same field and the richess of the view was very striking. An impressive object.
All in all it was a great night. This is the first time I've ever used a Dobsonian and I rather liked it. The finder on the club's Dob was broken from an earlier mishap and we ended up taping it together tonight. That made it a bit difficult to align it properly but with a little practice I was able to locate objects with it reasonably well. I found the 133x magnification to be a bit too high for the Dob... not due to limitations of the scope's optics but rather due to the scope's mounting. The Dob has no slow motions so the fine positioning necessary at the higher magnifications was tricky (but possible). Also the lack of an equatorial mounting (not to mention clock drive) was more of a problem at the higher magnification as well. Finally I had some concerns that there was light loss with the 25mm Plossel eyepiece. Optically the eyepiece seemed fine, but the large exit pupil made it look as if some of the Dob's collected light would be spilling out to the side of the observer's eyes. For very serious deep sky work a different eyepiece might be more suitable (not sure).
Overall, I found using the Dob a pleasure. It was easy and simple to deal with and the views were great. When I aligned the finder on Altair I got very sharp, well formed images (although I admit that I only used the 48x magnification).
Formal sky conditions follow:
<observation> <datetime format="ISO" timezone="EDT">2002-09-12:22:00</datetime> <location> <notes>Vermont Technical College. "Upper" entrance to the orchard across the street from the dorms.</notes> </location> <observer>Peter, Rob, Ed</observer> <sky-conditions> <weather> <notes>Cool, but not excessively cold. Observing without a coat was acceptable although perhaps a touch chilly. There were no clouds at the beginning of the session but some started to move in towards the end of the session (just past 10:00pm EDT).</notes> </weather> <limiting-mag> <value method="EST">5</value> <notes>The Milky Way was visible but not as intensely as I've seen it. Fifth magnitude stars in Cyg visible with averted vision.</notes> </limiting-mag> <light-pollution> <notes>The lights of VTC caused some washing out of the sky, particularly to the north. There was no real light pollution to the south or east (the west was blocked by trees).</notes> </light-pollution> <moon> <notes>The waxing crescent moon was setting. It did not cause any significant problems.</notes> </moon> <notes>A good night. Despite the proximity of VTC's lights, the sky conditions were still decent for deep sky objects. The site is largely protected from VTC by a row of trees and that helps considerably.</notes> </sky-conditions> </observation>