Monday, May 21, 2012

Ring(s) of Fire

I just got back from a great trip to see the 2012 annular eclipse. It was everything I'd hoped for! Nearly all of us in the northern California part of the path got lucky, and we saw the eclipse through mostly-clear skies. I've been interested in eclipses since 1984 (the partial version of which I saw during high school), and this was my first `central' eclipse. I'm still waiting to see a total eclipse - that'll be 2017, with a little luck - but this was a great `dry run' for that experience, I hope.

It might seem surprising that an aspiring astro-imager would only shoot a few iPhone images of the eclipse, but I decided to keep things simple and make this primarily a visual-observing experience. I knew a lot of other people would acquire great images and image sequences, so I decided to just observe the Sun through a safely filtered telescope, and to soak in the weirdness of the light all around me.

One of the highlights of the eclipse were the crescent- and ring-shaped images of the Sun that were cast onto the house where I observed the eclipse. These were produced by very small gaps between the leaves in nearby trees, which acted like hundreds of pinhole-projection setups. As the first partial phase got  underway, we noticed a few crescents:

As the Moon moved farther across the face of the Sun, the crescents became more obvious, and we started to notice the large ones cast by trees in a neighboring yard:

Even though annularity only lasted about 4 minutes, it was worth walking around the yard to see and photograph the rings shown in the first image. Having read Norm Sperling's piece about his `8-second law' for total eclipses, I knew it would be worth doing more than just staring at the annulus through the telescope. Also, I was happy to share the view through the telescope with some family, friends, and neighbors. Moving around, looking at the tree-projected images, looking through the telescope, and savoring the weird and wonderfully dim eclipse light, made the period of annularity really fun and memorable.

The thing I was most interested in, before the eclipse, was what the illumination around me would look like. I knew it wouldn't get nearly as dark as during a total eclipse, and from what I've read, that's not really quite a `nighttime' experience. It sounds like a total eclipse produces its own unique brand of day-meets-night. The light cast by the `ring of fire' Sun was wonderfully strange. The simplest way to describe it would be `much dimmer than usual', but that hardly says anything. I keep finding myself wanting to say things like `odd', `strange', and `weird', but in a good way. Perhaps the most noticeable thing was the lack of heat from the Sun. Prior to first contact, it was a pretty hot day, around 90F (about 32C). I was glad the backyard observing site had large shady areas in which to set up my telescope, before putting it in the sunlight. During the first part of the first partial phase, it was hot! But during the deep-crescent and annular stages, I'd describe it like this: `A warm-looking cool light'. The light didn't have a `cool color' like blue, but it *felt* cool, compared the hot late afternoon we'd been experiencing a short time before.

If there's one imaging project I wish I'd undertaken, it would have been to try and photograph the light on the scene around me. I wish I could have used a DSLR on a tripod, running through a variety of exposure settings, with a grey card and a color card in the scene, to try and reproduce the appearance of the `eclipse light'. If I do imaging during a future eclipse, like 2017, I think that's what I'd like to do. I'll rely on others to image the Sun itself.

All in all, the 2012 annular eclipse was everything I could have hoped for. We sweated the weather all weekend, but it worked out just fine. A ridge of high pressure allowed me to image some galaxies and M5 on the Friday night (more on that anon), and to observe the sky visually on the Saturday night. On eclipse day, we got lucky! There was a bit of high cirrus during annularity, but it didn't materially affect the views or the experience. And during the last part of the second partial phase, thick high clouds rolled in for good and all - what luck! I plan to be as flexible and mobile as possible in 2017, but this time around, everything was great. I was glad to hear that so many other astro-friends had great experiences, too. Here's to the shadow of the Moon!

Wednesday, May 16, 2012

The (Leo) Luminance Triplet

For such a dry winter, California didn't have a lot of imaging-quality skies in early 2012. We had some late-season rain and mountain snow, which was good for our hydro balance, but not so good for the spring galaxy season. I finally got out in mid-May, and spent a couple of nights shooting M65, M66, and NGC 3628, otherwise known as the Leo Triplet. Here's the result, sized for a 15" MacBook Pro screen:

This is what's known as a `luminance' image, which means it was shot with a black-and-white (or `monochrome') CCD camera, through a clear (or `luminance') filter. In order to make a color image, I'll need to shoot it through 2 or 3 color filters. If all goes well, I hope to shoot it through Red, Green, and Blue filters before the spring season slips away. The subexposures for this image were each 5 minutes long, and I shot about 50 of them over two nights, for a total exposure time of about 4 hours. As always, the imaging scope was an Orion ED80 f/7.5 semi-apo refractor.

This was also the inaugural imaging run for my new (to me) Losmandy G-11 mount. I got a great deal on it from a fellow Bay Area imager, and I spent the April dark-moon period learning some of the ins and outs. I feel like I can polar align, acquire targets with the Gemini 1 (Level 4) goto system, and I can get pretty good autoguiding. During the nights when I shot these luminance frames, the RMS error on my guider corrections was running about 1/2 pixel in both RA and Dec.

I processed this image in Pixinsight, making use of the new Batch Preprocessing script. Very handy! Many thanks to the folks who wrote that script. Also many thanks to Mike Schuster for writing the PSF Estimation script, which auto-picked hundreds of stars and gave me the parameters of the point-spread function, which I used for Richardson-Lucy deconvolution. (Deconvolution is a sharpening routine that I used to bring out some of the details in the galaxies.) The hardest part of the whole processing workflow was the noise reduction, which I did with Multiscale Median Transform. Once I had the noise somewhat beaten down, I could get a halfway-decent stretched image from the Histogram Transformation. I did a bit of HDR Median Transform, but not nearly as much as I might use on, say, a large bright nebula.

I hope to be able to get out and shoot some RGB color data if I'm lucky; it would be nice to add color to these galaxies!