by Marek Cichanski
Conditions were, hmm... quite serviceable. It was a little cold and windy, but not enough to ruin things. Observing was still quite do-able. When I arrived about an hour before sunset, there was a strong, consistent breeze blowing. It abated somewhat around sunset, although it never fully went away. I had brought my ED80 / Telepod rig, in case it was too windy to set up the 18". In the end, I set up both. I kept the shroud on the 18" hiked up, to cut down on the amount of sail that I presented to the wind, but the wind wasn't a big problem in observing, except at high magnification. Even so, I still used high mag at times - there were enough calm spells to make it possible.
There wasn't any dew. It was chilly, but dry. I'm not sure what the temperature did during the night, but it was 48 when I left at about 1 am. It seemed colder earlier, but I'm not sure if it really was any colder. I've noticed this many times at MB. It gets chilly after sunset, I put on all my warm stuff, it seems really cold during the first part of the night, and then by around midnight I feel quite warm. I suspect that it's just ME warming up, and not the weather. But, it's hard to say. There was an inversion - it was about 38 when I got down the hill - but no valley fog. Maybe the inversion settled down past us around 11 or 12?
Seeing was variable, but I would rate it at about 3 - 3.5 on my personal "out of 5" scale. Somewhat better than average. Transparency and darkness were decent for MB, mag 5.5 in the southwestern sky, halfway up to the zenith.
A digression - I've mentioned this before, but I have found the the Herald-Bobroff "BM" charts to be extremely helpful in estimating limiting magnitude. I just pick a dark part of the sky, sit down in a comfy chair with the chart on my lap, and see what's the faintest star I can see. (Yes, I use AV. No, I don't care. I keep the question real simple - can I see the star or not?) For me, this makes LM estimates fun.
Speaking of the H-B atlas, George Feliz, Peter McKone, and I had fun bopping around in Canis Major last night, using one of the "D" charts. George had just gotten an H-B, and we were looking at M46 and M47. George decided to delve into his new atlas, and he pointed out that there were a number of other objects in the neighborhood. I flipped over to the same page, and had a lot of fun object-hopping in this area. Here are the objects that I logged (18" Obsession, ParaCorr):
| NGC 2414 | 8:39 pm, 17 Nagler, small field to quarter field, considerably bright, estimated Trumpler class III 3 p. The cluster precedes a bright field star. There's a line of 3 field stars that lies just to the south of the cluster in an E-W line. |
|---|---|
| NGC 2423 | 8:52 pm, 17 Nagler, 3/4 field to full field, bright, estimated Trumpler class III 3 m. I often confuse this cluster with M46 when I'm trying to find M46/M47. I often see it before I find M46, but I get confused by the fact that it doesn't have a planetary nebula in front of it. |
| Rupinder 26 | 8:44 pm, 17 Nagler, pretty faint to pretty bright, quarter field, estimated Trumpler class IV 2 p. The cluster precedes a bright field star. It is shaped like an arrowhead pointing east, with the bright field star being the tip of the arrowhead. Whaddya know, a Rupinder object. Never logged one of those before... |
| Rupinder 151 | 8:48 pm, 17 Nagler, pretty bright, central field to 3/4 field, triangular shape, estimated Trumpler class IV 2 m. |
As we were noodling around on this D chart, I remarked that this is probably my favorite overall type of observing. I really enjoy it when I have a good chart that shows a number of do-able objects in the same area. Hop, log, hop, log... very nice. Overall, I really like this H-B chart. I have memorized about a third to a half of the symbology, which is kind of fun. The best thing about it, though, is the use of line weight to show the overall visibility of the object. That is a real godsend. It really allows one to develop a mental 'calibration file' of what's visible in, say, a Montebello sky, or a Fremont Peak sky. So far, I'm digging this atlas.
Actually, the reason that we were looking at M46 was because of a bizarre shootout that I was doing. Since I had brought by ED80, and had set it up to look at the sun in H-alpha earlier in the afternoon (quiet sun, not much to report), I took advantage of having two scopes. It was great! Yes, the extra setup and teardown is an issue, but with an ED80 it doesn't add much. First, I pointed both scopes at M46 and gave them the same magnification. I'll bet you can guess the result - the 18" made the object look brighter than the 3" did. It was really interesting to compare the views like this, though. Both were in 82 degree apparent fields, both were at 120x. The 3" scope was really being pushed beyond the appropriate magnification for this object. Oh, it was there all right, and in some ways it looked good, but it was like trying to get a good picture out of an underexposed negative - the data just wasn't there. I've often noticed that open clusters show what I call "false nebulosity", as though there were unresolved stars hanging about. Well, that may have been partially the case in M46, but it wasn't really the whole explanation. Now I know that it's just some sort of artifact of looking at an OC with too high of a magnification for the aperture. It was also very interesting to look for NGC 2438(?), the PN in front of M46. I could just barely spot it with AV in the 3", but it was prominent and structured in the 18". It was surprisingly fun to do this rather ridiculous shootout.
I then experimented with mag-ing down on the 3". A while back, while hiking up Black Mountain on a blustery day, I passed the time thinking about magnification and apparent brightness. I started asking myself "if an object has a certain number of magnitudes per square arcminute (as seen in the eyepiece of the 18"), how much do I need to cut the magnification in order for it to show the same number of magnitudes per square arcminute in the 6 inch or the 3 inch?" After much hemming and hawing, I decided that the 'squared' factors cancel out, and that it's a linear relationship. Going to a scope with one-sixth the aperture? Go to a sixth of the magnification. Flash-forward to MB last night... I put the Terminagler on the 18", and looked at M46. I had hoped to say "ah yes, it looks essentially the same, just smaller". The reality? - well, not quite. Yep, it's smaller, Yep, it has a greater apparent brightness at 20x than it did at 120x. The 'false nebulosity' was gone. But, it didn't give the same subjective impression of brightness that it had in the 18". The planetary nebula still wasn't very easy to see, probably because it was now so apparently small. The end result... drum roll please... aperture wins. Wow, I'll bet I could knock you over with feather. Two long windbag paragraphs and the bottom line is that aperture wins.
On the plus side, though, it was a real kick to look at a spectacular widefield view in the ED80, and then go to the Obsession for the closeup. From 'refractor stars' to 'strewn with stars'. Life is way too good.
Peter and I found that the head of Hydra was a fun place to galaxy-hop, and I worked my way over towards Leo from there. We found that the NGC galaxy in the middle of the head was quite challenging. (It might have been 2466? Not sure, didn't log it...) I had to use the Millennium Star Atlas to find it. I also logged NGCs 2775 (nice and bright), 2713, 2716, 2718, and 2911.
After that, I mostly had fun. Bopped around Downtown Virgo, using an E-series chart in H-B. Very handy! George, Harry, and I were able to spot 8 galaxies in the same field at the beginning of Markarian's Chain. Had fun going back and forth along the chain, and then going over to M87. No logging, just fun galaxy-hopping. Doing that in Downtown Virgo is like those Donald Duck cartoons where Scrooge McDuck goes to his vault and jumps into his pile of money like it's a swimming pool. Lap of luxury time, for sure. It was also fun to show Harry the Sombrero and 4565.
I also looked at M3 at 470x in the 5 Nagler. This was more worthwhile than it might sound. When that sucker drifts (rapidly) into the field of view, it's a 'whoa' moment.
Also saw Omega Cen in both scopes, but it had just risen, and the stars were Nerf stars, even in the Obsession. Still neat to see, though.
Took many looks at Jupiter. The wind was a bit of a pain, but in between zephyrs there were some very nice views of the GRS. Lots of details in the equatorial belts. During the good moments, the moons showed nice round disks. One could begin to believe Clyde Tombaugh's claim that under the most perfect conditions, it might be possible to see albedo features on Ganymede. (Is an erupting Ionian volcano on the AINTNO list?)
Packed up the Obsession while waiting for moonrise, which took forever. It didn't come up at MB until about 12:40. Had a great view of it in the ED80. The backlit blades of grass looked as though a car was about to drive over the hill.
All in all, a pretty nice MB night. Coulda been a bit calmer, coulda been a bit warmer, but overall quite nice. Let's hope it's good again tonight.
Posted on sf-bay-tac Mar 31, 2005 10:48:56 PT
Converted by report.pm 1.2 Apr 05, 2005 20:08:58 PT