The Starry Night, 64

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9/28/2011. Clouds cleared just after sunset and tempted me to try to pluck a 30-minute exposure of the supernova in M101 out of the twilight and off the roofline. I began in a bright(ish) sky and finished my last five minute frame only a couple of minutes before the galaxy hit the trees. Stars were nice and tight, especially surprising with such a long air-path.



M101 with fading supernova
6x300s L

Surprise! That's one of my sharper images of M101. I didn't take the time to refocus. I just put the ST2000XM with the OAG on the AT10RC, calibrated the guider, and started shooting. I took darks and flats after the galaxy set. It's still the brightest star in the frame, but casual photometry says the SN has faded to about 10.8 since my last look.


M27, another try for the outer shells, this time with a 7nm Baader H-a filter. 10, 15-minute subs plus a set of 300s RGB gave me this, not-especially-artfully-composited image:


The outer shell material is just barely above background and can be found with reference to the more aggressively stretched negative image:

m27 inverted

10 x 900s 7nm H-a Baader filter
1x300s Baader RGB


Attempts to gather matching 900s RGB frames failed owing to bad trailing. The tattletale plot looked good, so something was moving. [In the morning, I found that the tiny grub screws that attach the rest of the OAG guiding head to the pick-off prism had loosened up. I cinched them down tight and resisted the urge to use SuperGlue -- which is fortunate given the mistake I discovered the next night.]


Finally for tonight, I wanted a reality check on plans to do photometry of Edwin Hubble's V1, a cepheid variable in the Andromeda galaxy.

Here's a stack of (only) three, 300s L exposures of the area. I stopped collecting data to refine focus and take RGB frames before resuming L collection. Clouds had other ideas, and the first three L frames are all the useful pixels I got tonight. Fifteen minutes of exposure through slightly hazy skies with a not-particularly-efficient CCD isn't quite enough. That shouldn't be a surprise, but it is a bit disappointing.



M31 with V1 marked
AT10RC, ST2000XM
3x300s Baader L

The star is there, but barely. An hour or so on a clear night should produce a nice, clean signal. I've dimmed the bright starclouds in the lower left half of the frame to emphasize foreground stars and dark nebulae in M31. I've also added this image to a former page (62) with a DSLR image and an AAVSO g-chart of the field.


9/29/2011. The sky the next night was more transparent than any in a very long time. Seeing was not great (around 2.5 arc seconds) while tracking was spot on (after I undid a mistake in reassembing the OAG -- helps if the pick-off prism faces the sky rather than the sensor). With an imperfectly aligned mount (and mine is almost always imperfectly aligned) you can reduce oscillations by correcting declination drift in only one direction. This requires some trial and error, but unidirectional dec corrections work very well when the technique works at all.

V1 does show up very well with an hour's exposure. It shows up even better with four. I added color (a single set of 300s RGB) which highlighted features in M31 very well: ruddy and swirling dust clouds, the older yellow stars of the hub, drifts of bright blue supergiants in the spiral arms. Note the two associations near V1, one is full of blue supergiants and the other is wreathed with hydrogen glowing red. The image shown is downsampled for the web:


v1 color

Hubble's V1 in M31
48x300s L, 1x300s RGB
ST2000XM w/Baader filters
Astro-Phyics Mach1GTO

9/30/2011. There'll be a change in the weather... lows in the lower 40's, upper 30's. 20+ degrees cooler than yesterday. It's breezy in the tops of the trees. The sky is clear but seeing is as bad as any in which I have ever tried imaging (a problem very nicely forecast by the Clear Sky Clock for an observing site about eight miles up river). I couldn't focus below about 3.5 seconds of arc, and there was some large scale motion involved, too. I thought at first from watching the tracking plot that wind was shaking the telescope, but down at ground level the air was not particularly lively. Clouds put an end to this comedy about midnight. Until then, I collected light from NGC 6992, the larger arc of the Veil:



NGC 6992, a supernova remnant in Cygnus
7 x 900s Ha (used as L), 1 x 300s RGB

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                   © 2011, David Cortner