Tuesday, October 24, 2017

A New View!

Long time readers know I'm justifiably proud of some of the Mirror Lab accomplishments, including the twin mirrors of the Large Binocular Telescope, each 8.4 meters (about 27.5 feet) in diameter. In particular, I've been on a quest of sorts of imaging the telescope while it does interesting things. It seems to have culminated last Spring when I caught the ARGOS laser propagating into the sky from a distance of 12 miles. From the town of Safford, through a small telescope, I almost had a front-row view of the instrument, visible at left, which is used to project a constellation of artificial stars in the field of view of the telescope to partially correct atmospheric turbulence. Several hundred similar frames were combined to make a short video seen here.

Well, without permission from the powers that be to get any closer (made more difficult by the recent severe fire this last spring that approached within 50 meters!), my most recent query was - from how far away can you see it?! From a post a few years back, I knew that LBT was line-of-sight from Kitt Peak National Observatory, very close to 120 miles away! The image at left is from that post and demonstrates that if you can see KPNO from LBT (flat-topped mountain in center), you can see LBT from KPNO!

So last night after work (working evenings this week at the Mirror Lab), I found my way driving westward - this after confirming with the LBT telescope operator that indeed ARGOS was operating properly. Being that it was dark-of-the-moon, I parked on the last pullout before turning towards the Observatory so that my lights would have no effect on operations there. It was an interesting night - totally clear, but obviously above an inversion layer. I watched the thermometer climb as the van ascended. It was 60F at the base of the mountain, 70F on top! The wind seemed a little blustery, alternately blowing out of the south or the north - weird! But fortunately, I was very comfortable in shorts and a long-sleeved t-shirt.

I had several optics to try - the first was easiest to set up - the 500mm F/4 "big bertha" telephoto. I had it up, pointed and focused on the lights of Tucson in a few minutes. It took me a couple shots to find where the LBT would appear - I'd never seen it from Kitt Peak, as it is quite small. But I knew it would be left of the red-lit radio transmission towers atop Mount Lemmon, so used that as my guide. About my 3rd shot - there it was! The green laser standing out from the occasional star and headlight visible on the Mount Lemmon Highway. At left is shown a 6-frame panorama of part of Tucson. with the green spot of the 18 watt ARGOS laser visible. At right is a single frame at a little larger scale better showing the laser beam.

I then broke out the big gun - the TEC 140 - a 5.5" diameter telescope with 1,000mm of focal length. Again, because of the large magnification, it took a couple practice frames to get it pointed properly. Note that at NO TIME was the ARGOS laser visible to the naked eye or even visible in the camera viewfinder. It was only the power of a 20 to 30 second exposure that revealed it was there. I had started an exposure sequence for a possible time-lapse, and interestingly, the inversion layer is visible just under LBT. In a couple minutes of exposure, it slowly dropped and became a little brighter in the less-affected air. Also visible in the exposure is the south slope of the mountain, brightly illuminated by the lights from Ft Grant prison at its base.

Most of my outings, I usually finish with a practice shot or mini-project that can be completed while putting away gear. This night, approaching 1:30 in the morning, I mounted the 16mm fisheye on the Canon 6D and took a couple frames of the sky from Andromeda to the rising Winter Milky Way. What is most interesting, besides the reddish airglow that looks like clouds to the west (right), is the oval glow just below center. This is called the Gegenshein, or counter-glow - a spot defined by being opposite to the sun in the sky. An optical effect allows sunlight to reflect from meteoritic dust back to us. This may be my best photo of it, and from only 2 stacked exposures shown here. Each of the 2 exposures were 2.5 minutes with the fisheye working at F/4.

Always great fun to be under a clear dark sky, and while chasing an ARGOS viewing might be only an excuse, it doesn't take much to get me out looking up!

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