The Starry Night, 31
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11/27/2010: Before driving with Amy to Tennessee for a delayed Thanksgiving dinner with the Tiptons, I set the A-P mount and 5-inch refractor into Park 1 position using an electronic level, then commanded the mount to Park 3, which is the outfit's most compact position, and covered it with a mylar sheath.
We left at 1:30, got home at 8:30 when I uncovered the telescope and asked for a slew to Deneb. I refined the polar alignment, then took the netbook outside, plugged everything up, and began a series of photos of the Double Cluster in order to make a direct comparison between the Astrodon Generation One E-series filters and the new Baader LRGB filters. I wanted to verify the effectiveness of Baader's anti-reflection coatings, and I took notes to decide which one filter provides the best starting point for 3- or 4-color imaging. It should not be a surprise that the B filter is not it. So far, the L filter seems best.
The Pleiades cleared the trees earlier than I expected, so I devoted some time to four, 6x300s sequences, one each in LRGB. I shot the half-hour of L first, because I thought it would be compromised more than the rest by the rising of a just over half-full Moon. All the data look pretty good. Here's the take, first L+B in monochrome, then RGB:
6x300s L + B (1 hr total)
Part of the Pleiades,
an open cluster in Taurus
Is Tennyson's "silver braid" an illusion due to imperfections of vision or an alusion to the nebulosity that does indeed entangle the Pleiades? The reflection nebula (especially the part near Merope, the leftmost Pleiad above) is easy to see in a dark sky using even small binoculars, but no visual experience really compares to the intricate braid shown in photos.
As for imperfections in the imaging train, I think it is safe to say that reflections in the Baader filterset are well controlled. After seeing this result, I had no qualms about trying a deep exposure of the Rosette nebula whose embedded stars are far fainter than those of the Pleiades. That advantage will become apparent when I add color data. Tonight, I started with the H-a foundation.
By the time the Rosette cleared the treetops, it was close to 3:00 AM. I experimented some with the Horsehead and the Christmas Tree cluster while waiting to get started. Being able to hop between NGC's and IC's this casually with the mount is wonderful!
I needed color data to do a good job with the Rosette, but I needed sleep more, so I set the telescope to shoot 3 hours of H-a in a dozen 900-second gulps beginning at 3:05 AM. I figured the last frame or two would be lost to dawn, but in fact all 12 were just fine. I got up briefly at 6:15 to unplug the kit and bring the computer inside. The temperature was 19F with a decent frost in the grass, which is pretty brisk barefoot and otherwise. The CCD held -30C with only a fraction of its cooling capacity (I think I saw 28% when I covered the control package and left it sitting on a heating pad under a Tupperware box for warmth and protection against frost).
Here's three hours of hydrogen-alpha of the Rosette Nebula. I'll add color by and by:
NGC 2236 - 46 (various), the Rosette
The first improvement suggested by tonight's adventures: arrange a timer to turn the telescope drive off automatically while leaving the computer and heating pad on. This was easily arranged using one of the digital timers that used to control the lights at my Mom's house.
The next improvement bears some thought: I need to make some kind of indexing ring or scale which would allow me to replace the CCD at a specified rotational position in the focusser. Ten degree marks from 0-90 degrees would probably suffice. A simple engraved ring for the CCD mounting tube and an index mark on the 2-inch clamp [vice versa would be easier] was my first thought. I'm still cogitating on what would work and how to make it.
Third, everything needs (even more) exposure. There's a good bit of noise in these images because I am still tempted to push them (too) hard when processing. Nice images also result with less aggressive processing, but the ones I want demand either more push or more light (and the latter is much preferred).
11/28/2010. I can't decide if it's going to remain clear or not. It's almost midnight, I want to go to bed, and I want H-a images of IC 443, "the Jellyfish Nebula." The Intellicast water vapor image suggests that the clear spell I see now may last, despite the scattered clouds that have typified the night until half an hour ago. Why did I buy the good stuff if not to use it? And I need the practice. Deploying the kit should be routine. I wondered if I could get started by midnight (20 minutes).
Didn't make it. It took 30 minutes to uncover the telescope, reset the meridian so I could begin with the OTA "under" the pier, recalibrate on M45, slew to IC 443, cool the imaging chip to -30C, frame, focus the guiding camera, select a guide star, calibrate the guider, focus the imaging camera, and begin a long series of 15 minute exposures (21x900s). Maybe the subject will move into the top of a pine tree and I'll lose the guide star (if that happens, it will be in the next hour). Maybe the sky will cloud up; maybe dew will blind the optics. Maybe all will be fine. At 6:15, the timer should cut power to the drive but power will stay on for the covered computer, its heating pad, and the guide and imaging cameras. We'll see what awaits in the storage directory (and out in the yard) in the morning.
The timer worked well. At 7:45, over coffee, I found the telescope stopped and aimed low to the SW, not at the horizon, not upended below it. Broken clouds filled the sky, and these quickly turned into a solid overcast. When did they arrive? According to the images waiting on the netbook, things began to go bad during the image exposed from 01:55 to 02:10. Then the guide star was lost and Eta Geminorum began a rapid drift ("rapid" being relative; it was still on the chip almost 3 hours later). Images after about 2:30 show only trailed images of bright Eta Gem and noise. Sometimes, the guider grabbed something. In fact, it seized on a series of different somethings, and the camera recorded either streaks, wobbles, or a line of seperate images of one bright star. Here's what I got before clouds thickened:
IC 443, The Jellyfish Nebula, a supernova
remnant in Gemini
That's promising, but no better than I got with less exposure a couple of years ago. This exposure is "thin," probably because of poor transparency, so think of this as an engineering test. The power cut-off worked. Stars are considerably defocused on one side which suggests that I need to reseat the 2-inch adapter and remove some of the spring tension in the bracket that locks the camera in place. If that doesn't do it... well, then, uhm... try something else. Note the large and familiar reflection around Eta. Try this field through the the 2-inch, narrower band, anti-reflection Baader filter mounted out at the nosepiece instead of the wider-band, uncoated, filter-wheel mounted Schuler. Finally, one of the USB cables caught on the rising camera and was under some tension this morning. Pay particular attention to how cables will move and potentially snag as the telescope rotates; as anyone who's used or configured a remote telescope knows, that issue deserves more than the passing thought I gave it last night.
11/30/2010. A little machine worrk. I thought about cutting out and turning a rotating bezel for the front of the camera adapter. I could engrave (or have engraved) several hash marks and provide for it to turn and lock down with a thumbscrew. But I think that is altogether too cute and a little wrong-headed. A simple printed and taped-on "setting circle" scale will do the trick along with a single line scribed into the 2.7-inch adapter.
I drew the scale in Photoshop, then resized it so that 0 and 90 were seperated by 1/4 of the circumferance of the spacer tube (which is 2.4 inches in diameter). Print, trim, encase in Scotch tape, then tape to the tube. Every composition is available somewhere on that quarter turn. This will provide experience to suggest whether cutting metal is necessary (or wise). Look here:
0-90 degree scale, graduated every 5
There's nothing especially precise or absolute about this scale; it's just a reference so that the CCD can be repositioned for multi-night efforts or when using filters not mounted in the filter wheel. The scale only has to be good enough to let automatic alignment software do its stuff. Still, the closer to actual E-W / N-S the end points represent, the better.
Other incremental improvements for today involved the camera brace and the tube used to maximize performance of the telecompressor. I added a couple of bends to the camera brace so that it does not torque the CCD when tightened down. Then I seperated the functions of its anchor bolt. That 2-inch 10-24 bolt formerly both anchored the brace and acted as a set screw to hold the 2-inch prime focus adapter inside the tube. (I know: I need to wave hands or provide cutaway diagrams for that remark to mean much. Sorry.) Now the anchor bolt does nothing but hold the brace, and a seperate set screw beside it locks the adapter in place. Finally, I drilled and tapped holes for three set screws near the camera-end of the adapter. I tossed the paper-tape shim (forgot all about that one) in favor of these three new set screws. They may aid in squaring up the sensor, or maybe they'll just hold the camera adapter a little more securely.
The Nikon lens mount on the CCD's faceplate has some discernable play -- probably enough to be a problem. Even so, there is much less flex in the entire rig now than there was an hour ago and less an hour ago than yesterday. Thus is progress made. (Remember to restock 10-24 set screws in various lengths.)
12/01/2010. Last night (in a steady, cold rain on the eve of December) I bought four brick pavers and some pea gravel with an eye toward establishing a semi-permanent location in the backyard to accomodate the trailer and its dominoes (when did I start calling those 6-inch blocks "dominoes"?) when in use. The trailer-mounted telescope and these brick footers appear to be what my long-cherished notion of putting up a backyard observatory has come to. Whether for good or "for the present epoch," we will see.
The lawn is sloped such that five 12x12x1 inch brick tiles are required: one under the E/W arm near each wheel of the trailer, and three under the tongue (Amy picked up a fifth paver while at Lowes looking for Christmas lights; it's item #19184). With three under the tongue, the dominoes can be arranged to hold the trailer in a level-ish orientation. Some good dirt and grass seed, and I should be able to make this perfectly presentable.
12/04/2010. Clear weather (at least a little) is in the offing this week, but nightly lows are forecast to drop into the low teens. Tomorrow night is forecast to be clear, 20F, with winds to 25mph. Taken all together it's time to get some remote control software running on the netbook.
This was a piece of cake using Access-Remote 4.12.1. I'm not sure what the current version is like, but this is what I used to use on the Vaio and it's what was already installed on the desktop. I had to name the Aspire One ("Ivy," short and sweet) and create an account through which to access it ("aspire1") and give the account a password (my usual for such purposes). I set the netbook to start the remote control software whenever Windows starts. Then I rebooted, came into the office and bingo! There it was.
I'll be able to change filters, take darks, ask for exposures, monitor guiding, keep an eye on the battery, etc. I shall be able to live large while taking data. With another USB port out there, or a hub, I could control the mount to retarget the telescope. With yet another, I could tweak focus, too. But the prospect of damaging cables and driving it into trouble means I'd rather be present when slewing, at least for now, and as long as I keep to the LRGB filters or to the H-a filter, I should not need to refocus too often. All this is good. This is very good.
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