Special Observing ReportMonte Bello: May 29, 2002
I had been hoping for a night like this. Moon approaching rebirth. Clear blue sky by day. Light winds. Cool temperatures. It all added up to what could turn out to be the finest night of seeing in over a month. And I had just the spot to observe from - Monte Bello.
"Why Monte Bello?", you ask. Surely, Backyard Boulder Creek gets darker skies. And if you really want to "run deep", head on up to China Ridge or better yet - drop by astrobud El Marko's "deep sky sanctuary" on the Bonny Doon Ridge.
But no, I was willing to sacrifice the half magnitude gained from the backyard, and the full magnitude from El Marko's or China Ridge. Why? Like most astro's I sometimes appreciate a crowd. And I was pulling for Monte Bello to finally get a "knock your observing socks off" night.
Did I get it? Yes and No. Though the Monte Bello Open Space Preserves parking lot held its fair share of vehicles and equipment, there was plenty of room to spare. And though the sky was decent overhead and passable to the south, there still was that "rim of illumination", swinging around from the northwest to the southeast.
Aside from observing out of MB on one of its finer nights, there was another story unfolding. And that story was El Marko's. For you see, that very day El Marko had received his TV-85 back from Televue in New York where it had undergone "remedial action". That action consisted of righting the lens cell after it had mysteriously gone out of alignment. El Marko was looking forward to seeing if the astigmatism detected last month after comparing views seen through Dan's Tak, AstroTalk's Vicki, the Pup, and Argo had been banished.
And last night El Marko got his answer.
We arrived around 9:00pm. We parked adjacent to fellow TACo Phil who was hiding behind a 10 inch dobsonian. (Quiet, I wasn't supposed to tell anybody.) But Phil wasn't the only astro sporting a "rocker box". Across the parking lot a 12 inch Discovery Dob was set up. El Marko and I debated the aperture. I thought 12, El Marko, 10. El Marko headed off to nail down the facts. And while I setup the 80mm Pup, Mark conversed amiably with the owner.
By the time El Marko returned, I had almost completed my pre-skydark doubles tour. At 275x, nice airy disk on Antares - but the primary's diffraction rings were just too rapacious to distinguish the green companion. Delta Cygni however, gave a more promising result. There it was, a "faint bluish brightening" on the first diffraction ring southwest of the second magnitude primary. Nothing definitive - but close. El Marko was hesitant to turn the 85 on the Double Double, but the Pup is never at a loss on this pair. Results are sky condition dependent only. And on this occasion the matched Epsilon-2 pair were cleanly distinguished at 120x. Meanwhile, the E-1 disparate required a bit more concentration. El Marko wanted to give the scope a little more time to "chill" before the attempt...
With the advent of true skydark (around 9:45) turned the Pup on M13. Several dozen faint 11-12th magnitude stars stared back at me. A fine view and a tribute to the roughly 5.5 ZULM skies hanging overhead. The Ring too gave an excellent view - with the annularity well aspected against the black of 120x space. In making the usual telescopic limiting magnitude check, found that the 12.3 reference star in the "Challice of the Ring" asterism just dissolved on direct inspection. Telescopically, the sky was magnitude 5.8 deep overhead and the Pup was holding stars down to magnitude 12.0.
It wasn't long after this that El Marko took the plunge and we had our first look at the Double Double. Splendid 140x resolve! Three small balls of light joined by a tiny fourth. Later we ran the magnification up to about 250x, and there in the yawning gulf between the two doubles shown clearly and directly the 12.0 and 12.5 magnitude comes. Truly an accomplishment for a three and change incher and again a tribute to the depth and stability of the sky.
I also had look at the Ring through the 85. At 140x the background sky was ebony-black. The Ring stood in high relief and the 12.3 mag test star could just be held direct.
Later El Marko and I turned our scopes on M22 in Sagittarius. Both scopes resolved several dozen menmbers easily, but the TV added that extra touch of "pointillism" and "contrast" that often distinguishes a fine apochromat from an good achromat.
The mood to catch a few rapidly westering Ophiuchan globular clusters missed earlier in the month came over me. It was "heads down" time. First on the shortlist list was 10.2 magnitude NGC 6235 - located well out in the hinterlands of Ophiuchus north-northeast of Antares. This is one of those "you can't get there from here" studies. There was just no good way to turn it up. So after several abortive attempts to hop along a series of stars from Theta Oph, I made an effort to pick out 5th magnitude 24 Oph and triangulate off a nearby 6th magnitude star to its northwest. The cluster proved to be an extremely difficult, but definitive find. At 48x, could just make out a faint, diffuse, and slightly condensed sheen some 15 arcmins southwest of a triangle of 9th magnitude field stars. Direct observation could not hold the cluster. So this one was "on the edge" - right where I like to find 'em.
Two more remained. Both located near Tau Ophiuchus - well north and east of 6235 in a region much more amenable of approach. 10.3 magnitude NGC 6517 lies southwest of Tau and proved every bit as challenging as its predecessor. The cluster formed the eastern apex of a small isoceles triangle including a north-south pair of 11th magnitude stars. Like NGC 6235, no real structure discernable. Like NGC 6235, It too lay just this side of the edge.
9.6 magnitude globular cluster NGC 6539 takes a position at the northern apex of a finderscope triangle that includes Tau and a neighboring 5th magnitude star. Locating the field was quite simple. Center the crosshairs at the expected locale. Switch over to the one degree 48x field and bingo: There you have it - one of the most starless regions ever encountered anywhere near the Milky Way. Nothing resembling a cluster in sight. Bearing an average surface brightness of magnitude 13.6, this 7 arc minute sized cluster is outside the "phase space" of sky and scope.
But this does not mean the cluster could not be viewed... Earlier in the evening El Marko and I had a made the acquaintence of Jake. And it was about this time that I dropped bye for a visit with Jake and his C11. So we punched in "NGC6539" and had a look at this critter. Now normally an 11 inch scope will do a decent job of revealing structure - even some resolution - of a sub 10th magnitude globular. But 6539 would have none of this. What jake and I saw was a "vague quarter-sized" diffuse blob of gray light lacking much in the way of condensation. Thus the reason for the 80mm Pups failure was revealed - there was simply no part of this particular cluster bright enough to reveal itself to a scope limited to magnitude 12.5 (under aversion) at 48x.
So the bulk of the night's mysteries were resolved. El Marko's TV-85 now lived up to a pair of "optophiles" expectations. On its best night's the sky at Monte Bello could give some sassy deepsky views. And 4 arc minute sized 10th magnitude globular clusters could prove consistently susceptible to 80mms of unobstructed aperture. But one more remained...
For even as I sought my trio of globs, Phil and James were making a painstaking search for globular cluster NGC 6496 east-southeast of Theta Scorpii. Despite numerous starhopping and field jumping attempts nothing globular rvealed itself. Ultimately, one final trick was employed: What the heck is this thing supposed to look like anyway? So referencing software on Phil's laptop, we had a look at the cluster. And cluster it wasn't. Just a vague grouping of brightish stars - no nebulosity, no compact "beehive" of resolved stars nothing. What astronomer in a sober state of mind would categorize THAT as a cluster.
After packing up the Pup, and as El Marko was doing likewise with the TV-85, visited with Ben. Ben had been doing some imaging using an SBIG 10 and 4" AP Traveller. During the course of the evening, he had captured a fine view of the Trifid Nebula. It seems fitting to conclude with a link to the image on his website.
Enjoy.
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