Staring @ the Sun, 51

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06/05/2012. Me and my baby view the transit of Venus. Again.
For the 2012 transit of Venus, we dragged the A-P mount, the 5-inch A-P refractor, the Lunt solar 'scope, plus a computer, deep cycle battery, and assorted bits 300 yards to the west, up and out of our holler, to where the setting Sun would shine down a piney colonnade. And we got... clouds, mostly. At 6:04, a few minutes before nominal first contact, I found the Sun and a tiny notch in its NE limb. Bingo! Venus against the bright chromosphere, dimly silhouetted against the innermost corona. I thought, focus? And I punched Robofocus. OK, enough, now grab the clip. Recompose? No! grab the clip! Just let me tweak the focus one more time... No! Grab the clip! And I did. Likewise, I captured a second video during the next brief clearing (distilled image shown below). A third clip a minute or two later caught a few seconds of the transit being swallowed by intricate, dramatic clouds. Thirty minutes later, through a fourth fleeting clearing, Amy saw the transit in the eyepiece of the A-P, and I stole a glimpse before rushing the Canon 50D onto the A-P just in time for a few frames. Here's what I have so far, while Pacific and Asian observers watch the end of the show and a steady rain falls here just after midnight:


Lunt 60THA50DS, PGR Chameleon
100x34ms, 6db
Best 258 of 400 frames manually selected with HandyAVI, best 100 of those used by AVIStack 2.
Registax for wavelets, Focus Magic for deconvolution, color in Photoshop


transit 2

Hope springs eternal. Or at least for a couple of hours.



...and is duly rewarded!
0.4s, Canon 50D, A-P 5" F6, iso 200
Thousand Oaks visual solar filter.


Video clips: All the images I'm going to get of the 2012 transit have to come from the source files behind the following video clips. The originals total about 1.5GB, so these have been trimmed down for the web by a factor of about 500. There's 56 seconds of video containing something other than a blank screen because of clouds. That's it.

I was exposing "hot" to get something through thin clouds and to try (successfully!) to get Venus silhouetted against the chromosphere beyond the visible solar disk. As a result, the big active region at the bottom of the frame is overexposed when really clear air comes along. I can probably pull detail out by selecting sharp frames in which clouds act as neutral density filters if it ever seems important for the composition. So far, it doesn't.

Have a look. This and a two minute clear spell about half an hour later when we admired the view (and when Venus was full on the disk and nowhere near as interesting, I think) is all I saw of the 2012 transit of Venus. It was enough, I think, to get some good images, but this time around I am going to earn every pixel. [For 2004's easy trick, click here. It was "762mm and be there." Project for the summer: compile the places around the world that ran it.]


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 Ingress begins.



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Ingress continues.



The portion of clip 2 which was refined into the image at the top of this page can also be processed to yield this ghostly image of the planet silhouetted against a few faint prominences. Look just above the gap in the chromosphere at the left side of the frame:


venus outside sun's disk


Here's the critical portion of the image at full resolution, with a matching key. On the right, I've added a white circle outlining where Venus blocks the sun's atmosphere:









06/08/2012: Venus near inferior conjunction, redux. It's a little more exciting trying to shoot Venus as the planet moves away west of the Sun into the morning sky than it was as the planet approached from the east. Now, if the telescope drive stops for any reason, the Sun will glide into the field of view a couple of minutes later and cook whatever sensor happens to be watching, electronic or protoplasmic:



Venus in near IR
Baader IR-pass filter (670 - 700nm)
0.27% illuminated, 4.3° from Sun


No fancy poles or aperture masks this time, just a long "dew"-shield to knock off the worst of the direct sunlight. I decided to follow the example of experts and use deep red light to minimize turbulence. This seems to be effective. Note the narrower crescent in these two similarly processed images. The bloated crescent in these photos is essentially the sum of seeing-smeared images of the hairline crescent, and there is less of that in the near IR image. The Baader continuum filter has a 10nm FWHM bandwidth centered near 540nm. The near IR filter's bandpass opens near 670nm and is centered at 685nm. If the filter's band continues into the IR, it's moot because the Maxbright diagonal closes the window at 700nm:





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Except where noted, solar photos are made with a Point Grey Research Chameleon camera behind a Lunt Solar Systems 60mm THa solar telescope double-stacked wtih a 50mm front etalon for an achieved bandwidth of about 0.55 Angstroms. The telescope uses a B600 blocking filter and is mounted piggyback with an Astro-Tech 10-inch Ritchey-Chretien (carefully capped!) on an Astro-Physics Mach1GTO mount. An Acer Aspire One netbook running Point Grey's Flycap software provides camera control and capture services via USB 2.0. Images typically begin as 20 second AVI's captured at 15 fps. 300 frame clips are aligned and stacked using Registax 6 or AVIStack 2.0. The resulting files are processed via wavelet functions in Registax and / or the FocusMagic 3.0.2 deconvolution plug-in in Photoshop CS4. (PixInsight is rapidly supplanting some of those steps.) The imaging train usually includes an Orion "Shorty" 2x barlow screwed into the 1.25-inch prime-focus snout. Exposures are on the order of 4-8 ms with gain set to 10-12 db, or 12-18ms at 0 gain. The barlow is sometimes replaced by an Antares 0.5x telecompressor sandwiched between the 1.25-inch snout and the C-adapter on the PGR Chameleon; this produces a full-disk image (during most of the year) and allows exposures in the 1ms range with slightly less gain. A RoboFocus motor with a timing belt looped around the stock (or, sometimes, a Feathertouch) focus knob enables remote operation.



                   © 2011, David Cortner