Another Learning Adventure!

On Thursday after a long day in the Arizona Cancer Center keeping Melinda company for her latest round of chemo, I was ready for a drive just to get out of town. The IV drugs they administer help her with the immediate side effects of the chemo for a few days, so knew she would be ok at home. They make her a little sleepy, so likely she would relax at home, surrounded by cats.

For my adventure, there was a bright moon, so no astronomical imaging of the usual sort, but I'd been keeping my eye on ARGOS from a distance. ARGOS is an instrument on the Large Binocular Telescope (LBT) and stands for Advanced Rayleigh guided Ground layer adaptive Optics System. In short, a laser makes an array of guide stars around the field of view and instrumentation partially corrects the distortion caused by turbulence in the atmosphere over an extended field of view. Most large telescope's artificial guide star systems work over a field of view of a few arc-seconds, but ARGOS corrects a field of 4 arc-minutes, a huge improvement. I've blogged about it before - the 18 watt lasers can be seen for many miles, and with post-storm clearing, I was hoping to get another chance to take more images. The image at left shows an shot from 22 miles away that I was hoping to improve on. This image, taken on 8 November, 2013 resulted in a blog post, but the images taken with a 200mm lens at left and the William Optics scope showed some color shifts, and even though I had intended to do a time-lapse, I never attempted it with all the work involved.

So I made the 90 minute drive, arriving just at dark, looking for a site a little closer than that I used before. I quickly found a nice quiet deserted site a little off the paved road. Unfortunately, my first exposure showed that the only cloud in the sky was found hugging the profile of Mount Graham, my target! Shown at left through the 200mm lens, it was pretty close - stars were above the mountain, but residual moisture from the storm left a defiant cloud cap. Staff on the mountain had found the season's first snow the previous day, and I know from my experiences on Kitt Peak that even the humidity that sticks around after the clouds dissipate would likely keep the scope closed. Fortunately, this trip I had the phone number for the console room of the telescope, so could use my cell phone to find out directly what was going on! And the operator Thursday was Geno - who I've worked with occasionally a couple decades ago when he worked at a metrology place here in town. Geno confirmed they were, indeed, in a cloud cap and were unlikely to open anytime soon, because of humidity as above... Oh well, it was such a pleasant evening too!

Well, since I was there, I got out one camera anyway and took a few frames. My first shots of the night provided a learning moment for me! I saw Ursa Minor with Polaris nicely placed so thought I'd take a short exposure of it. After carefully focusing on distant farm lights, I pointed it up to Polaris and took a 30 second exposure. My eureka moment was seeing not pinpoint stars, but little wormy trails. While I had carefully turned off the autofocus feature of the lens so it wouldn't go hunting for focus in the dark, I had NOT turned off the image stabilization (IS). For longish exposures (30 seconds here), the corrective optics get lost and drift, resulting in trailing star images. I corrected the issue and re-exposed, shown at left. The inset is from the exposure with IS turned on and you can see the effect. Also in my sky, the Big Dipper asterism was hugging the horizon, so I took a 2-frame panorama to capture it and Mount Graham. The lights are from local farms and the nearby community of Fort Grant. The Dipper is at left and the cloud-capped Mount Graham is at right. There is an artifact from the vignetting of the two images that result in a darkening in the center...

With the bright moon and little chance of LBT and ARGOS making an appearance anytime soon, I decided to head back to Tucson for an early evening of it. I got back pretty much right at 9pm. The next morning, I got an e-mail from one of the engineers that said that was about the time they were able to open the telescope... Which was ok, because with that late start, taking a couple hours of images would have resulted in a return time well after Midnight. Will try it on another time...

But when searching for the topmost image on my last ARGOS imaging session, I returned to the files taken nearly 2 years ago. I've spent the last day or two going thru them and making the time-lapse I had hoped to. On that trip, Melinda and I recorded about 2 hours of images through my 70-200 zoom set to 200, and also on the William Optics scope, with 770mm of focal length. The former had 1 minute exposures at F/3.5 and the scope needed 2 minute exposures working at F/7. I do not know the details of the program that night, but they apparently were set up on the same part of sky for those hours. Also visible are a number of planes, cars going to and from the mountain, and of course, the LBT can be seen rotating to keep the object in the field. It apparently was tracking something just north of the zenith as the dome was turned north, not south towards us. Since I've got a new telescope with more focal length (the TEC 140), I'm ready to try it again when I get a chance. Enjoy the time-lapse - watch it full screen in HD if you can...