11:50 p.m. 26 May 2000 PDT (0650 27 May 2000 UTC)
A recent protracted illness wasn't life-threatening, but it was still serious enough to keep me from observing for more than a month, much to my frustration. Of course skies were generally clear during that time. As I mentioned in a post on SAA, one of the hardest things to do is to start up again after a period of inactivity, and one way that I find it easier to succeed is to have some specific observing program for when I do return.
My targets, then, for this first night back in over a month were some bright Messier globulars. That is, they're normally bright under dark skies, but observing them under a bright Los Angeles sky provides its own challenge. This evening, the zenith limiting magnitude was about 4.6, plus or minus 0.2. However, I was targetting M3 and M5, and at midnight from my home over here on the west side of L.A., the limiting magnitude in that area of the sky is a bit lower, about 4.4. I didn't attempt a rigorous assessment of the seeing, but it was negligible at the lower magnifications (only up to 100x) that I was using.
First up was M5. I find it at the right-angled corner of a 30-60-90 triangle between alpha Serpentis and epsilon Bootis, also known as Izar. Izar is a splendid double, but I didn't look at it this evening. After spotting up that triangle corner by using the finder as a reflex device, I looked through the main scope at 52x. Nothing. I strained a while, knowing that it could be lost in the murky light pollution.
Not a chance, as it turned out. I tried scanning in RA, from left to right, and as it turns out, M5 is startlingly bright, even under suburban skies. There were two features that I could see, both striations in the otherwise smooth texture of the globular. One was a streak running north from the core and bending to the northeast. The other was a second streak running southwest from the core and bending to the west. Modulating the magnification on my zoom eyepiece revealed the optimal magnification under these skies to be at 12 mm, for 104x. I compared it at that power with M13, which was also up at the time, and M5 certainly didn't suffer there. It is every much as impressive a sight as the Grand Old Hercules Cluster.
M3 was next. For some reason, although M5 is prominently featured on the Sky and Telescope centerfold map each month, M3 is nowhere to be found. It is somewhat dimmer, to be sure, but it's still easily seen through light pollution. I found it at the third corner of a 60-60-60 equilateral triangle whose other two corners are Arcturus and rho Bootis. I almost couldn't find it at first; it turns out to be rather close to a 7th-magnitude field star.
Use of the zoom showed best detail at 18mm for about 69x. It seemed to have significant mottling at the center, which I thought might have been a chance occurrence of stars, since it is otherwise smooth. There was a trio or quartet—I couldn't tell, exactly—somewhat west of center, with one lone bright star east of center.
When I was done, I came in and consulted my copy of Stephen O'Meara's guide to the Messier objects. I must admit it was gratifying to see that he had seen the same features as I had (as well as some others, to be sure!). It's good to know I'm not just making this stuff up!
11:30 p.m. 26 June 2000 PDT (0630 27 June 2000 UTC)
We've been doing a lot of home improvement work, and the skies haven't cooperated either. Enough excuses, though—it was time to do a quick observing session, mostly to review old targets but also to try a new quarry.
Sky transparency was fair: limiting magnitude was about 4.8 at the zenith, about 4.6 in the area where I'd be working the hardest, in—ah, but you'll have to wait a moment for that. First up for Opus was Vega, high overhead, for a moment's collimation. The waddling scope had held its collimation pretty well over the last month of disuse, so it only took about a minute or so to correct it to my satisfaction. The star danced somewhat, revealing about one-arcsecond seeing.
With this adjustment done, the first real target was the Double Double, or epsilon Lyrae. It was clearly split in the eyepiece I used for collimation, the 9 mm ortho, for 139x; it was also cleanly split in the 15 mm Plossl (83x) and the 24 mm end of the Vixen zoom (52x), but the 32 mm Plossl (39x) only showed some elongation. To convey my idea of a clean split, let me say that in Opus's 5-inch aperture, the Airy discs of the southern pair were distinct, but the first diffraction rings of the two stars appeared to be touching.
My two review targets were M57 (the Ring Nebula) and M27 (the Dumbbell). M57 was surprisingly bright through the suburban light pollution, and showed its usual corpuscular or "smoke ring" appearance. I felt the UltraBlock (Orion's narrowband filter) made M57 easier to see, but didn't uncover any extra detail. M27, on the other hand, was dimmer than I thought it would be. The UltraBlock did show some improvement; the nebula appeared rectangular without the filter, but with the filter in place, a bowtie or black-widow shape was superimposed on that rectangle.
The tough target of the night was M71, a dim, small globular in Sagitta, and that is where I figured a limiting magnitude of 4.6. Stephen O'Meara, in his book on the Messier objects, gives its distance as 13,000 light-years, and its magnitude as 8.0 (as opposed to a "classical" magnitude of 8.4). Its closeness and sparseness would probably have given it a granular appearance under darker skies, or with a larger scope, but under the circumstances, I was merely trying to see it.
That indeed was the right challenge. Sagitta is primarily composed of four stars in the shape of an arrow, but there are two other stars in the arrow that are somewhat dimmer. M71 is near the easternmost of these two. My observations were made with the 8–24 mm Vixen zoom, at a variety of magnifications and with and without the SkyGlow filter (Orion's broadband filter).
I tried at first without the filter, but nothing showed, not even a dim smudge. With the filter in place, it was sometimes difficult to find the right focus point, for the stars too were dimmed by the filter, but it seemed to show a slight brightening in the right location, especially at 16 mm (78x). Removing the filter once more gave me my best view of M71, at 12 mm (104x). Hardly any detail was visible under these conditions; the only feature I could make out, and it was tentative, was a northeast-southwest striation along the southern edge of the globular. O'Meara's drawings certainly show no such feature—in fact, if anything, they have a northwest-southeast streak at that point.
Copyright (c) 2000 Brian Tung