The Starry Night, 38
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12/25/2010 So let's talk about this White Christmas thing. See, the last forecast before the snow began was for 1" on Christmas Day (Saturday), maybe another 1" that night, then clearing skies by Monday night or Tuesday. Six and a half inches of snow, most of them unexpected, might not be much of a deal to my friends in Minnesota, Ontario, Ohio, and other alien climes, but let me tell you: that's enough to cause some excitement in the mountain south.
At 11 AM on Chrstmas morning, light snow began to stick. Fine, thought I, I'll just leave the telescope set up under its cover and be ready when the sky clears Monday or Tuesday. Let's go watch "Polar Express," and maybe "Millions," or "Love Actually," and not worry about it.
By 4:00, the forecast had changed for the better (in a Burl Ive's kind of way), but with the air full of fine, slightly damp snow, I didn't want to uncover the telescope and its attached electronics. Nor did I want to try to roll the fully-assembled outfit across a steep, icy lawn into the basement.
By 10 AM on Boxing Day, we had six or seven inches on the ground, with a little more in the air. In a lull about 24 hours after the snow began, I went out to bring the optics and the CCD inside and to make sure that the electronics under the blue Tupperwire bin were dry.
No problems anywhere. The TeleGizmos cover worked great and the stuff under the Tupperware was bone dry. If I wanted to make a habit out of this, I'd replace that light sun-cover over the telescope and mount with a TeleGizmos 365 series all-weather cover designed for permanent outdoor use.
Enough whining. Monday night is still supposed to be clear, not so cold (low 20's), and breezy (30mph winds gusting to 45). We'll see. If that forecast is as far off as the one I relied on, the temperature might be either -20° or +80°, and the wind could be calm or 90 per. As long as it's clear, I promise not to complain (much).
12/27/2010. Try some more guider options: If the sky is indeed clear tonight, use the Shorty barlow threaded directly into the DSI. That might be a nice compromise between field of view and guiding sensitivity. The barlow in its ordinary configuration requires that the focuser be racked out almost as far as possible (see photos above). It can't be particularly solid. A wide field of view (such as when using the ST80 at its native FL) is nice because it lets me use the guider as a digital finder for initial calibration on twilight stars. The extra guiding scale is not needed with the A-P OTA which is guided just fine at the native 400mm. It might be needed for some future OTA, though, and it will be good to know what works.
In fact, for the 538mm EFL's at which I've been imaging lately, try guiding with the Antares telecompressor on the guider (which produces a just under 200mm EFL) and see how that goes. Given the effectiveness of sub-pixel guiding on calculated PSF centroids, it should be just fine. It means very little extension and a very wide field. Well worth a try.
After squinting, recollecting, and measuring some, it's entirely possible that the 2-inch TeleVue Big Barlow will not offer an accessible focal position for the ST2000XM with the A-P nosepiece and CFW-8a. It is even less likely to do so now that the thicker Muscle Plate is fronting the CFW-8a. Even if I do find an accessible point of focus, the field may be excessively curved (the last point is taken from the A-P catalog regarding their reservations about using their Barcon for deepsky photography behind fast glass; it may apply to larger film formats more than to the relatively small ST2000XM chip). Small, dangerous thought of the day: I'm considering threading my own extra lock screws into an A-P 2.7 to 2-inch converter. How hard could that be? [Piece of cake, see below.]
Winds are not as bad as predicted, but they're enough to fill the air with fine ice crystals. The low tonight should be in the upper teens. Tomorrow the ice should be gone and the air will be ten degrees warmer. Reluctantly -- it's very clear! -- let's wait a day to try more imaging.
12/28/2010. After the snow... with the Shorty Barlow screwed into the nosepiece of the DSI (same way I use another Shorty Barlow screwed into the nosepiece of the Point Grey Chameleon for solar photography), the guide telescope has an EFL of 749mm. The focuser still seems too extended to inspire confidence, but I'm using it that way tonight to guide photos of the two faint nebulae near Gamma Cassiopeia, IC 59 and IC 63. An hour and change in, the guiding performance in PHD is the best I've ever seen (Osc-index 0.01, RMS 0.10; maximum excursions appear to be +/- .2 pixels but see note below for a post mortem on that). I'm guiding on a 10th magnitude star, one of the brightish blue stars between the two nebulae.
I thought tonight's targets were reflection nebulae, but from the first three images, a 900s RGB triplet, they look very much like emission nebulae. I should try an H-a exposure, but tonight I am committed to RGB and L data. I'm taking L frames for the rest of the evening.
Gamma Cassiopeia is the middle star in the "W" of Cassiopeia. Here are its two fading companions:
Gamma Cassiopeia, IC 59 and IC 63
After the fifth luminosity sub, high thin clouds began to drift over. I took another couple of frames, and one might add something other than noise to the view. The clouds wouldn't've mattered except that Gamma Cas puts out a lot of light to scatter and these IC's are faint. Then I captured a few 120s frames so I could eventually mix down the overwhelming brilliance of 2.1 magnitude Gamma Cas (about 10,000 suns, 610 light-years away), and I took a fresh dark frame, just because I could. For the moment, let's go with this.
I feel the urge to mess about in a BOTE. Those clouds are on the order of half a degree, or one hundredth of a radian, from Gamma Cas. At small angles, the angle is equal almost to the sine and the sine to the tangent, so at 610 ly distance, that angular seperation corresponds to about 6 ly (assuming they and the star are coplanar). If those clouds are 100x closer to the star than I am, then the star looks 10,000x brighter from their vantage. The magnitude scale is based on the fifth root of 100, so a difference in flux of 10,000x is 10 magnitudes (requisite logs and exponentiation are left as an exercise for the reader). Gamma Cas is about mv 2.15 as seen from Earth (it's a variable star, so that changes some), so from the distance of those clouds, it shines at -8 magnitude, or about 40x brighter than Venus in our skies, as bright as a substantial Moon. And a great deal of its light must be in the ultraviolet spectrum. It's pretty impressive that it's eroding and ionizing those clouds from that distance.
I think there may be some interesting dark nebulae above and left of the second brightest star in the frame. On a clearer night, it'll be worth trying some very deep imaging in this area. A flat would help, and I'll leave the rig intact until tomorrow so that I might get one.
I did not realign on the pole before tonight's session. Almost all the guiding corrections were in the same direction. I should've taken a clue from that and had a look at polar alignment, because Maxim has a terrible time aligning these subs. Two star manual alignment is really the only way to go with the L frames.
In other news...
I modified an older A-P 2.7 to 2-inch adapter to use 3, 10-24 socket head screws rather than its single thumb screw. This may help with the (few microns of) sag which CCD Inspector measures and which shows up when using a laser collimator. Next flex to think about: I caught the ST2000XM trying to rotate slightly under its off-center weight while I was preparing last night's run. Maybe I should do something similar with the Feathertouch clamp? Or think about a counterweight [done, from aluminum hex stock and some flat bar stock; it also serves as a handle and cable organizer; film at 11. I tried to rebuild this using a 1-inch steel bar as a more compact counterweight -- took 90 minutes to gnaw my way through it on the lathe, aiming for 5.00 inches in length; I got 6.05. Got to measure those initial cuts Just A Little Better. And as for the 3-bolt adapter, the laser collimator suggests that the newer adapter with the compression ring clamp holds accessories straighter. The 3-bolt version is more secure, but "secure" isn't the problem (if there is a problem) while squareness might be. However, if I replaced the bolts in the 3-bolt ring with set screws I think I could reduce the EFL more by gaining considerable in-travel for the focuser, but by how much and why?].
Would PEMPRO be a worthwhile addition to the software kit just for its polar alignment tool? Possibly, considering that I don't anticipate a permanent pier for the outfit and would welcome the ability to use more of the lawn, including areas from which Polaris is inaccessible. I'll download a 30-day trial copy the next time there is the prospect of several clear nights over which to give it a try. [Wait! There's also PoleAlignMax, which is freeware but which appears to require me to configure computer-based goto, hence a serial adapter, more cabling, another USB device.... But wait again! Why don't I just learn to use the alignment procedures outlined in the A-P manual using the GTOCP3 software? They are good enough for Roland, and they are good enough for you.]
I downloaded a beta program which purports to provide a front-end for scripting Nebulosity sequences. It worked great the first time I tried it (I called for 5s LRGB and dark frames which it produced as neatly as could be), but it has not worked properly again since. I'll work on that some after the first of the month and see if I can get it tamed. More when I know more. The ability to set a long series of LRGB frames would be very nice. According to the Nebulosity docs, this can also be done manually using a text editor. Also, I've done this in Maxim DL, but if I could do it without leaving the comfortable and cushy Nebulosity environment, better.
The effective focal length of the telecompressed A-P with the Mandel Muscle Plate replacing the stock front plate of the CFW-8a is shortened by 1mm to 537.4mm.
A cheap fleece from CVS now covers the computer when in use on its heating pad and serves as an added layer over the telescope when throwing the TeleGizmos cover over it.
The weather better clear
up soon before I get completely caught up
Also at CVS, I picked up some 91% isopropyl alcohol, the Canon-recommended variety for clearning lens contacts, and used that to clean the gold connections on the 17-85mm AFs IS which has been giving me communications errors on all bodies lately. I dampened a paper towel with the alcohol and thoroughly swabbed each contact using a dental pick. No more problems.
The repaired and cleaned 50D came home from Steve Swearingen of The Camera Clinic in Sparks, NV. Works like a charm. Google them for camera repairs!
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