The Starry Night, 230

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Too many clear nights in a row!

09/22/2022. I am worn out. But I have to use them, or else I can't kvetch about NC's weather when it returns to its usual pattern. This afternoon, a tiny, pop-up shower erupted just for us. I scrambled outside and covered the delicate bits of the observatory and got utterly soaked in the process. I took it as payback for "complaining" about too many clear nights in a row. In cloudy twilight, I took an improved luminance flat, then covered the kit for the first time in several nights.

First, some housekeeping. I changed the way I store image files. I have to grab data in 2-3 hour snippets because of my pine-restricted sky, so if I file the captures by date, most targets' data are spread out across multiple directories. This makes it feeding Pixinsight harder than it needs to be. Starting with September 1's data, I've begun storing raw images in directories named for the subject, the instrument, and its EFL ("M31_pile_AT10RC_1200MM") rather than the date of acquisition. "Pile" means it's a pile of data from multiple nights.

I reworked the Orion ST80 for better guide images. I swear to god, I think the objective was mounted backwards after I took a cleaning fit many years ago. I turned it around (and cleaned it while I had everything apart). When I ask for multiple guide stars now, sometimes I get 6, 8, 10, or more rather than 2 or 3. Stars are actually reasonably starlike on the guider's sensor, and there are, of course, so many more.

I removed the diagonal I'd been using behind the X:Y stage which made everything nice and compact, but I don't think it helped in any other way. I used instead a short extension tube to hold the guide camera and cranked the focuser out to the 37mm mark. Is that the best way to get this extension? Images are sharper on-axis than off (duh...), so don't go twisting the offsets unless you need to. But then I need to know where it's aimed when the stage is set near offset 0:0 (found it, will mark the stage so I can easily return to zero offset from the main OTA's point of aim).

I saved some guide camera images to see just where the ST80 is pointed. At a guess, I think it's aimed about three quarters of a degree from the main 'scope.

At a measurement, it was offset more like half a degree from the main OTA. That's easily within the range of adjustability of the X:Y stage. I tweaked the alignment and marked the X:Y stage in order to be able to return to 0,0. This reminds me that I need to improve polar alignment, not for guiding, per se, but to reduce image rotation when using off-center guidestars.

Note to self: in case you need to know, the guide scope has a FL of 402mm according to the astrometry script in PixInsight.

The combination of tracking outside the main image and my decent but still only approximate polar alignment produces field rotation that's easily visible in a 15 minute exposure when subs are stacked without digital alignment. It's just discenable within each 180s subframe. At the moment, this is the biggest cause of my elongated stars. These are the perils of finally getting really good guiding and tight, 2-3 arc second, stars.

Today's improvements are measurable, and maybe visible: I'm seeing guiding in the 0.15 - 0.25 pixel range, which is more than twice as tight as what has counted for excellent so far this year and calculates out to about 0.3 - 0.5 arc seconds. Because all was set up, I took a short run on M56, and left it all to carry on overnight with NGC 7331 and Eduoard Stephan's Quintet.

(The next night, I took M13 with the guider and the telescope agreeing on where to look. Also NGC 6888. And NGC 7331. Analysis to come.)

Enough housekeeping. Let's look at some pictures.

SpaceX launched 54 Starlink satellites into orbit during evening twilight. Here's the launch, with notes about each photo.

[1,2,3 SpaceX photos]

Almost exactly 24 hours later, the payload came around in a magnificent twilight display.

[Starlink chain]

Apart from that, Messier and NGC objects attracted my attention. I routinely started one target in fading twilight, changed to another about three hours later, and then another, and then left the telescope to its work the rest of the night. The AC power outlet timer works well; the shutdown utility on the computer (and the auto screen-off settings) saves a lot of battery life.


[NGC 6960]



[NHC 7331]

[M31, a couple of ways]

There are a lot of ways to put that much data (and more) to work. I have decent starts if I can just find the time to show them off! Hurricane Ian ought to give me some rest.

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My deep-sky photos are made with a variety of sensors and optics. Deepest images come now from a ZWO ASI1600MM Cooled Pro CMOS camera, an ASIair (model 1) and sometimes one of several laptops. A good many images come from an unmodded Canon 6D but a lot more will be coming from an R6. Video and video extracts begin in a Canon EOS M, usually running in crop mode via Magic Lantern firmware (but the 6D and especially the R6 will probably see more use). Telescopes include an AT10RC, an Orion 10" F4 Newtonian, and a pair of apochromats: a TMB92SS and a AT65EDQ. A very early Astro-Physics 5" F6 gets some use, too. So do lots of camera lenses on both the ASI1600 and on the Canons. A solar Frankenscope made using a 90mm F10 Orion achromat and the etalon, relay optics, and focuser from a Lunt 60 feeding a small ZWO camera will see more action as the Sun comes back to life (Autostakkart!3 is my current fav for image stacking). Mounts include an iOpton SkyTracker (original model), a bargain LXD-55, a Losmandy G11 (492 Digital Drive), and an Astro-Physics Mach1. PixInsight does most of the heavy lifting; Photoshop polishes. Some of the toys are more or less permanently based in New Mexico. I desperately hope to get back soon.







                   © 2021, David Cortner