Observing report for 8,9,11 October 1996

Location/Conditions

Gear

Objects

Comet Hale-Bopp, Comet Tabur, Gegenschein, M31, M32, M33, M110, North America Nebula, NGC 752

Report

I'm in the second night of a 6-night observing run at Kitt Peak so to rest up for a tiring eighty hours of work in six days, I was sort of taking it easy last week. Thus, I had my evening free to do some silly things like amateur astronomy ;). This is a long-winded report based upon the three nights I obseved and photographed up in the mountains. My equipment consists of a pair of Bushnell 7x50s, a Bushnell 60mm f/11 refactor (both of sufficient but not great quality) a Minolta X-7A 35mm SLR with several lenses, a single-arm barn-door tracker based upon the design in the July 1987(!) Astronomy magazine, and glasses with -6.5 diopters of correction ;). (I was shooting Fuji Super G+ 800 all three nights).

Spurred on by two naked-eye comets, I finally decided to test out the Snowy Range west of Laramie as an observing site. I'm trying to get back into amateur astronomy, mostly thanks to Hyakutake. I've been extremely busy the last several months (typical grad student life), but we've had a spell of remarkably good October weather, and as mentioned in the first paragraph, I had some free time. Thus on Tuesday evening I headed for the Snowys, 30 miles by air from town.

The Snowy Range proper is basically a few-mile long ridge line, which is nearly vertical in places on the southeast side which faces Laramie. Below this are several alpine lakes, and a seasonal paved road winds it's way through the area. By about 7:30pm, I had found a very good spot well of the main road at Mirror Lake at about 10500ft above sea level. The horizons were mostly unblocked, except for the bottom 1/4 of the northern sky blocked by the steep mountain slopes. Most important, the line of sight to the main road was almost totally blocked so headlight pollution wouldn't be a problem. With such good weather, and given the location, obviously the transparency was great (more on this later).

The first target of opportunity was Hale-Bopp. I can't say that I was terribly impressed (the memories of Hyakutake are still fresh), but a 1.5-2 degree fan tail in the 7x50s still makes it one of the better comets I've seen. I didn't attempt to make a precise brightness estimate, but it seemed about 5th magnitude like everyone else says. I shot three photos with the 135mm lens at f/4, but they weren't very impressive. I also shot a 9 minute exposure of the summer Milky Way setting behind the mountains. This showed a lot of Mikly Way, but alas, as I had somewhat expected, the used 28mm lens I recently purchased is crap for astrophotos. And besides, I caught *three* jet aircraft in the frame.

For freedom from the manual tracking for a while, I took a couple of star trail photos, which finally gave me time to stargaze. I was really wanting to make a careful limiting magnitude estimate for the site. I asked about this here a while ago, and one of the things I was going to try was counting the number of visible stars in areas of the sky bounded by relatively bright stars. When I tried this for an area nearly overhead, I was rather overwhelmed by the task because there were so many. Thus, I decided to fall back on the north polar chart in the RASC Handbook. I know I was in trouble when I saw a couple stars that weren't on the chart :). I ended up barely being able to see the +7.1 star near Polaris pretty much everytime I made a concerted effort. The closely packed +6.5, +6.6, and +6.1 stars in the upper right of the chart were fairly easy. After this, a quick check yielded a naked-eye sighting of M33 (comparable to seeing a +6.5 or so star).

After some more general scaning, I stumbled upon the Gegenschein in Pisces, which was actually rather noticable; actually easier than M33. I think I was seeing part of the zodiacal band extending up and to the right but this was hard to confirm. The North America Nebula region was naked-eye visible, and both M32 and M110 were easy binocular objects. The surprise naked-eye object of the night was NGC 752; it wasn't particularly difficult, but I had to look it up in Uranometria to figure out what it was.

Unfortunately, while taking a 20 minute star trail photo, my batteries died in the near freezing temperatures. It was about 10pm and I had had a long day so I decided to pack up and leave.

I decided to head back on Wednesday night. I wasn't feeling quite as well early, and I wasn't able to see quite as faint early on. However, by about 10pm, I was able to acquire the +7.1 star again. The air was dead calm (and the temperature dropped below freezing by midnight), so I took a couple of pictures trying to see how well Mirror Lake would live up to it's name. These turned out pretty good, but the amount of light pollution from Laramie was surprisingly large for being 30 miles away. In addition, light pollution to the north was noticable in a 30 minute exposure of the mountains silhouetted against the northern sky. The only sensible source this is I-80 about 15 miles away; there aren't any towns big enough to be that noticable. The recent dry and breezy weather might have also contributed to a larger than normal amount of particulate matter in the air which may have been a factor.

I stayed later this time, and observed Comet Tabur as it rose over the mountains after midnight. Most interesting was that in the pictures I took of the two comets, Hale-Bopp was distinctly yellow while Tabur had the same blue-green color of Hyakutake. This would be explained by greater dust output in the former.

I didn't get the pictures from these two nights developed until Thursday, and most of the tracked photos showed large tracking errors as compared to, for instance, the Hyakutake shots I took. The tracking on those was as good as I've ever had using the tracker, presumably due to the sub-zero cold. I had an unpleasantly large amount of dental work done at 8:30am on Thursday after getting home at about 1:30, so I skipped Thursday night.

On Friday I worked on the tracker a little bit and with the few cirrus clouds of the day moving away, I headed for the mountains again. This time it was windy, but much warmer; good because the first gaffe of the night was forgetting to bring a pair of gloves. At times I used an extra pair of wool socks that I brought, but at times I just went without. The other problem was much more serious. I had been noticing that the sheath on my cable release was fraying, but hadn't really though too much about it. Unfortunately, after taking a couple of Hale-Bopp frames, the cable failed. Uh-oh; that's the only was I can take long exposures. A round trip back to town would take 1.5 hours and I would have to try to find a friend with a spare cable. After about 15 minutes, I managed an unexpected kludge which allowed me to have the cable end constantly touching the contact in the camera. I could then use the on/off switch to start and stop each exposure. Phew!

The main goals were to get a great shot of the North America Nebula and to record the Gegenschein. However, my tweaking of the tracker didn't work and the picture were bad. I did get some more good star trail photos (it's hard to screw these up). This night the limiting magnitude was 'only' about +6.9, possibly due to the poor seeing. M33 and the Gegenschein were still no problem, as expected. This night I had my 60mm refractor, but it's unstable mount was no match for the 25mph wind gusts.

Final comments. Although this is the first time I've ever identified a 7th magnitude star, I've had skies as good or nearly as good while growing up in southeastern Iowa. It really ticks me off how so many guidebooks all but say "don't even think about trying to see the Gegenschein, you dolt!!!". I'm sure I could have seen it several times as a kid if I had known to try. I realize that for most people a truly dark site isn't easy to get to, but even the RASC Handbook says that a +6.4 limiting magnitude is a "superb" sky, which is an overstatement, IMNSHO.

On a lighter note, I wondering whether this was nearly as good as it gets for this site, or if I can push it out to +7.5 or more naked-eye. Part of the problem is that there are a lot of 7th magnitude stars that don't have accurate photometry. I'm looking into this and I'm trying to come up with a better north polar chart based upon published photometry. I'm also hoping to make a naked-eye estimate here at Kitt Peak, but I've been solo the first two nights so I can't leave the control room for long enough to dark-adapt. I have a student I was supervising last summer coming up for the weekend so if the weather holds I'll try this weekend.


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