You may be wondering why binoculars are worthy of a Peripatetic Traveler blog post. What if I told you that this particular pair is 5000 x 8408 and consists of two mirrors, each of which is about 27 feet (8.4 meters) in diameter? Would that pique your interest?
Yesterday, I had the opportunity to tour the Large Binocular Telescope (LBT) on Mt. Graham in southeastern Arizona, not far from the town of Safford. The tour was conducted by Dr. John Hill, who is the LBT’s technical director. He is also a member of the Tucson Rough Riders and sets up this tour every couple of years as an official club event.
We left Tucson shortly after 10 AM and caravanned east on I-10 to the junction of US 191 (north), which is a bit past Willcox. About 30 – 35 miles later, we turned left onto AZ 366. We regrouped at the Base Camp complex, after which we drove up to the telescope itself. Just before the pavement ended, we stopped for a late lunch at a “scenic view” pullout. This was our view toward the west:
After finishing lunch, we all piled back into our vehicles for the final few miles to the top of Mt. Graham. The mountain is about 10,700 feet high, which made it significantly cooler than Tucson. When we arrived in midafternoon, the temperature was in the 50s, and by the time we left shortly after sunset it had dropped to 34. (By contrast, it was right around 60 in Tucson when I got home at 9:30 last night.)
This is the telescope enclosure. The green part of the building is stationary; the white part is the enclosure itself and rotates with the ‘scope – but is physically separated from the telescope by a small gap in order to minimize or eliminate any movement due to wind.
After touring the lower part of the building, we took an elevator to the “transfer level.” This is the top level of the stationary section, where people going higher have to switch to a second elevator that is wholly-contained in the upper (moving) section. Then we went up another level to the telescope room.
Like any pair of handheld binoculars, the two mirrors of the LBT are separated. This photo shows the central part of the telescope assembly. The shiny arcs are the load-bearing surfaces on which the whole instrument rides; they’re physically separated from the base during movement by a microns-thin layer of oil. This oil layer reduces friction to the point that four 3-hp electric motors (a total of 12 horsepower) can move the whole thing 90 degrees, from horizon to zenith, in just over a minute. Even when you’re standing right next to it, you can’t hear it move.
Each mirror is mounted to one side of the assembly; this photo shows one of the mounts.
We were able to climb up on one of the catwalks behind the telescope and look down on the mirrors. This is the “right hand” mirror, seen from the top. All of the light that it captures is reflected up to one of two devices: a collector, or a secondary mirror that focuses the light back down through the center opening in the big mirror to a third (flat) mirror below. The third mirror redirects the light to the instrument(s) in the center of the telescope.
This is what the right side looks like with the whole assembly rotated to a zero-degree elevation (so it looks at the horizon).
Just before sunset (around 5:10 PM) they opened the main doors. Then they rotated the telescope (with the building following along) to make sure everything was working smoothly. It was.
By this time the temperature had dropped from chilly to COLD. With an unobstructed wind blowing through the building, the wind-chill was probably in the lower 20s, if not the teens. Despite this, I was surprised to learn that they often run the telescope room’s A/C almost every day. The reason is because if the telescope isn’t at ambient temperature (i.e., the same as outside), then there will be air currents around the ‘scope that will distort the incoming view. “Ambient” ranges from, say, the 60s in the summertime to below zero in winter, but it’s not the absolute temperature that matters – it’s the difference between the outside temp and the telescope’s temp. So they typically open the doors before dark to help cool off the structure and scope. It gave us a perfect view of the day’s sunset:
Some of us left shortly after; others stayed for a while to look at the stars. Either way, it was a fantastic day and tour, and an opportunity to see something that most people can’t.
[Please note: Any inaccuracies in my account are entirely due to a faulty memory and not to any misinformation that Dr. Hill gave us on the tour.]