Special Observing ReportObserving At Large: March 31, 2002
China Ridge
By quarter to six, was on Big Basin Highway driving west from Boulder Creek, CA to China Ridge Road. Ten minutes later, began bumping and swerving my way toward the northern loop of Big Basin Highway. Destination: China Ridge and a now little used (by me) turnout thereon which presents expansive views southeast to southwest.
This was to be my first visit to the China Ridge observing site since last summer. Had no difficulty finding the spot. By sunset Argo was all setup. That tree to the west would be problematic. It was unlikely that I was going to be able to turn up M74. But M77 remained a possibility...
No, I wasn't planning a Messier Marathon. I hoped to get a sense of how susceptible these two studies would prove some one week after the vernal equinox. Then I'd be off to track down the Great Andromeda Galaxy and a few other much descended studies as well. With luck and by Moonrise, I'd have gone on to enjoy a few "full tilt" studies in parts of the sky obscured from Backyard Boulder Creek...
But I wasn't attached to my plan. Already that sprawling tree to west had disabused me of expectations of success.
But success can be measured on many levels...
While absorbing the beginnings of dusk, a young family pulled up in a minivan. Young, smiling couple with two beautiful children emerged. I pointed out the breach in the mountain ridge west of us. There the Pacific Ocean peeked through. A low mist enshrouded what appeared to be frozen waves in the distance. Those binoculars had already proven themselves an invaluable addition to the evening's kit.
"Goh Mop Sumnida". And they were gone to enjoy the rest of their vacation in these United States...
A few minutes later two other groups arrived. Again the binoculars proved their utility. A quiet sense of goodwill pervaded this visitation as well. Nature has a way of bringing out the best in people. Nothing in the way of "red in tooth and claw" here!
Finally I turned to greet a mountain biker who had rolled up unawares. Drawn by Argo, this particular visitor was clearly interested in astronomy. And no wonder, the "stranger" turned out to be a fellow member of the Santa Cruz Astronomy Club. At first I didn't recognize him - the context wasn't quite right. And of course, riding gear and sunglasses also make cognition a little difficult.
It wasn't long before the evening's observing venue changed dramatically...
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Bonny Doon
Mark headed down Big Basin Road while I packed Argo in the hatchback. Park headquarters is located maybe ten kilometers from where I'd setup. Paid a lot of attention to the inside shoulder of the road on the drive to headquarters - never makes sense to run over hospitality.
Mark must have made serious time on the tarmac. I overtook no cyclists along the way. This surprised me given the distance involved. After five minutes, Mark pulled up and we pointed our vehicles east toward Jamison Creek Road. The drive was brisk. Nightfall preceded apace. Always a tortuous route, we encountered numerous switchbacks and doglegs. The climb up and up led to Mark's preferred Bonny Doon observing locale. Argo was setup and ready for pleasure not too long after skydark.
The sky was quite deep - especially given the twin hits of a passing lunacy and the "dust across the waters" experienced of late. (A huge dust storm occured west of Beijing China on the 22nd. Dust plumed high enough to enter the jetstream. It then took the 10K kilometer fast lane to Northern California. OK you Martian amateurs, write and tell us how much you liked the Earth's version of last opposition's "maria obscura"...)
As deep as Mark's sky was, seeing stability was marginal - maybe 6/10. (Could barely detect Saturn's Cassini. Three belts visible in Jupiter's cloudtops.) Later in the evening, made a 52x threshold limiting magnitude check using my favorite 12.7 magnitude star in Praesepe. Could just hold it with moderate aversion.
After 220x views of Jupiter and Saturn, Mark and I started tracking down a few deepsky studies. Started with reflecting nebulosity in the Pleaides. This brightly scattered cluster appeared embroiled in a "gauzy haze" everywhere we looked. Certainly atmospheric water or aerosols could account for it. By sweeping well away from the brighter stars, we found a very definite region of concentrated nebulosity. Without expectation, we dropped the ultrablock filter into the 35mm ultrascopic. Although the background sky darkened perceptibly, no improvement in nebular contrast was seen. As one might suspect, "reflecting nebula" are generally absent the kind of ionization needed to radiate in the hydrogen alpha and forbidden oxygen bands.
From our spot, Orion was partially obscured by trees. Before long, Alnitak emerged. With ultrablock filter in place, only the brightest lobe of the Flame Nebula could be seen. Removing the filter revealed the main dark lane that splits the nebula in twain. We made no effort to seek counsel from the "Horse's head". It would take Arizona skies to locate such an faintly-traced obscuration through 150mm Argo...
It wasn't long thereafter when the Great Nebula emerged. Definite nebulosity extended well out toward the western field stop of the 50 arc minute eyepiece. Little nebulosity was seen to south and east. Adding the filter made east-extended nebulosity perceptible. Mark commented that, although the filter had revealed more extensive nebulosity, some of the texture had been lost. It's possible that the various tufts and folds seen in the Great Nebula are of the reflecting rather than the ionizing type. Should make an interesting study to follow up on in the future...
Mark went on to explain that through his 12.5 inch dob, the M43 region takes on a decidedly reddish hue. Although this hue was not visible through 6 inch Argo, it was clear to us that M43 nebulosity lacks the kind of "blues" seen in nearby and overpowering M42.
Sweeping the field north of the Great Nebula we noted the nebulosity (NGC1973-5-7) enveloping a pair of stars just south of brightly scattered open cluster NGC1981. The cluster itself included a nice widish evenly-matched double I didn't recall seeing previously. Before leaving the Hunter entirely, dropped in 120x to get a look at Alnitak. This closish, mildly disparate pair is tough through marginal skies. And that was the case this evening. The two stars remained an oddly shaped unity...
Mark had heard of our next study but had yet to see it. We started our foray by dropping in on the Castor pair. At 120x, and even under 6/10 seeing stability, very cleanly separated. Mark was more impressed with the view than it warranted in my estimation. Then I learned why. Mark has yet to see how stars look under fine conditions. Large dobs don't often show airy disks with concentric diffraction rings. One reason is the fact that high magnifications and dobsonian mounts do not make for a good pairing. Another, is that the airy disk seen in a fine 12 inch scope is about .8 arc seconds in diameter. A third reason: Fast newts, and large scopes in general, lack the kind of optical train integrity needed to reveal airy disks. Still another is that atmospheric distortion is an area function while resolution is linear. As a result, the kind of sky stability (7/10) needed to reveal airy disks is rare for large scopes. And finally: Larger scopes collect far too much light from bright stars to form airy disks at the eyepiece. Generally a scope capable of magnitude 15 reach needs to be turned on 5th magnitude stars to show that .8 arc second airy disk under scope-centric 7/10 seeing. The upshot: Mark hasn't really seen much of airy disks...
Although Argo shows wonderful airies, the seeing wasn't up to it. So the Castor pair (almost too bright for Argo's 13 magnitude reach anyway) appeared a pair of flashing jewels of light in the night. And Mark didn't get to see the 1.6 arc second star disks Argo is well capable of revealing...
Having viewed Castor, I dropped in the 52x eyepiece and slewed north to pick out the two faint stars that situate near the Intergalactic Wanderer. This 10.4 magnitude, 4 arc-minute sized globular cluster is located more than 100KLY from the Earth. Very nice view. Easily held direct with central condensation. Best had yet through Argo in a while. And of course, Mark could only be thinking, how really well it might look in that 12.5 dobsonian...
Praesepe now lay well overhead. Dropped in to made my check. Too large a cluster for Argo at 52x. This one belongs to the Pup. Several nice wide doubles and triples.
M67 was another matter. At 52x took up maybe a third of the field. Much more of "beehive" than the Beehive in Argo. But the cluster looked somwhat more "spherical" than recalled from last year.
Somewhere in here, Mark navigated me to a fine fifth magnitude "star of color". Probably a carbon star, X Cancri presented the typical "pumpkin" color to my eye.
Mark and I then set sail for Hubble's Variable Nebula. Easy enough to locate. Pick out that Christmas Tree Cluster then drop south-southwest. Vaguely cone-shaped nebulosity with faint 11th magnitude star located toward the apex.
After a break from observing, we caught the first glimmerings of Moontide. The sky was loosing it quick. Settled on the M81/82 region. Took in the two fainter nearby members as well. Then on to the Leo Trio. Through the moon-washed sky only the two Messier's could be seen. On to M3: Only a few stars resolved at 120x. And these required extreme aversion.
Earlier in the evening we had taken a look at the closish Theta Auriga disparate pair. Resolvable at 120x but uninspiring. Better were 24 Coma Bernices and Cor Coroli. These "pairs of color" are too well separated and matched in brilliance to suffer much - even as the sky completely fell apart.
So Mark and I settled in for a chat while waiting for the Moon to clear the trees. Once it did, there was nothing especially inspiring about it. A couple of fine craters could be seen along the terminator. One resembled an old-fashioned "juicer" - the kind you press a half-orange into and rotate by hand. Huge, well-illumined central peak within a foreshortened "rim" of luminosity. Mare Crisium appeared half-engulfed in shadow. A single frozen wave, crested its broad surface. But there was no real clarity to any of the features. I had hoped to be able to show Mark Shroters Valley to the east, but between sky position, seeing, and lunar phase, nothing doing.
While packing up the scope, I reflected on how much the sky had changed over the course of the evening. Early on, countless stars swarmed the heavens. In fact, so many that my hard-won (hardly-won) ability to navigate celestially was impaired - both unaided and through the finderscope. Later that luminously gibbous Moon had all but evicted the brightest stars from the sky. Nothing renained up there to hold my attention any further.
Biding Mark "Sleep well", I was off...
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