Saturday, April 29, 2017

A New View of LBT!

It is never my intention to go a month between blog posts - it just seems to work out to that lately - I have no excuse! Case in point is this post about the Large Binocular Telescope (LBT) - the photos were taken nearly 2 months ago! I was initially looking for permission from their director to ok the release of the images, but after so long, I guess I'll be looking for forgiveness rather than permission if they complain!

I feel sort of possessive of the LBT telescope as I supervised the polishing operations on the primary mirrors. Entering "LBT" in the upper left search window will return a number of posts, including some on the ARGOS instrument - my current favorite. ARGOS, of course, stands for "Advanced Rayleigh guided Ground layer adaptive Optics System" - an instrument mounted on the telescope that uses lasers to focus 10km above the telescope, those artificial "stars" are used to analyse and correct the atmospheric turbulence along the path. It really is exciting stuff, as it can improve seeing over a relatively large (up to 4 arc-minutes) field by a factor of 2 or 3.  While a factor of 2 or 3 doesn't sound that groundbreaking, note that the INTENSITY or brightness of a focused star goes up a factor of 4 or 9, by improving the sharpness that factor of 2 or 3.  Improving your star detection ability by a factor of up to 9 really is a big deal! This post really isn't about the instrument, merely observations of the lasers involved. For more information of the system and results, even from this run, go to the Max Planck Institute site - the sponsor of the instrument.

There was an ARGOS run in early March. With fresh snow on the mountain, I didn't even consider an observing site on Mount Graham, instead, went to the town of Safford, some parts of town enjoying a direct view of the telescope. I had obtained telephone permission to observe from the Discovery Park campus, but their view was a bit too obscured, so moved about a mile eastward for the good view shown above right at about sunset. You can see in the photo if you go west or north, the rise to the right of LBT starts blocking it. From my vantage point, LBT was 12 miles away - the closest I've been for an ARGOS run! The image at left shows my setup - from 2 sturdy tripods I was running a 500mm lens on the Canon 6D (full 35mm format) for a wide angle shot of the telescope, and the TEC140 (1,000mm with Canon XSi APS format) for the narrow field-of-view.

Looking very carefully at the above image, the laser projecting upwards from near the peak of Mount Graham can barely be seen. It was much more obvious through the optical aid of the telescopes and telephotos! At left is the view through the 500mm. Coupled with the larger format of the 6D, it gives a very nice wide field of view.

Through the TEC140, as with the photo at the top of the post, lots of details can be seen, including antennae in the sunset shot above! I took a series of photos with both setups, typically 30 second exposures under the nearly full moon was sufficient to get a good histogram. In the wide shot above, a wisp of clouds can be seen hugging the mountain. There was a layer of smoke that I suspect was from a controlled burn from the Tucson water treatment plant. The "Sweetwater Wetlands" had a burn of vegetation to control mosquitos, and can be seen as an enhancement in the laser scatter just over the telescope in some of the shots.

I chose to use only the narrow field in making the time-lapse of the evening, since the details were so stunning. In addition, I was able to start taking images before the dome opened, another advantage of knowing the phone number of the telescope operator and getting briefed on the observer's plans. So shown here are about 270 frames taken over a 3 hour period covering the dome opening, setup and following the first object of the evening. While it looks like the telescope is tracking across the sky much more slowly than the stars in the field, realize we are looking just over the horizon with a considerable focal length while the telescope is looking much higher in the sky.

Note that at no time was the green beam of the ARGOS laser visible to the naked eye. Even in my decent pair of 9X63 binoculars was it barely seen. Of course, as seen above, it photographs well! Finally as I was driving home with the telescope on its second object, I could barely detect a "green star" from inside the enclosure directly by eye, but that was all that was visible in my nearly 4 hours there! I've heard rumors that locals are upset at the lasers, but as you need optical aid to detect them, it hardly seems obtrusive! At the same time, with the gains in observing efficiency they are seeing it is proving its worth.

Before leaving, I took a few frames of the Discovery Park campus a mile to the west from my location. It is a cool place with interesting displays of both historical interest from the region, and the ground-breaking science going on at LBT and the optics from the Mirror Lab, including a cool 20" Tinsley telescope in the dome. Shown here is a 2-frame mosaic illuminated by ambient moonlight, and some security lights on the grounds that give it a nice glow...


Anonymous said...

Very cool Dean. I see why I couldn't see the laser from a scratchy plane window. (Kevin Bays)

Anonymous said...

Great pictures. Thanks for posting! Fire phasers Mr. Sulu!