Friday, March 24, 2017

Tucson, AZ - Mirrors Into the Past

Our second stop of the day was at the Caris Mirror Lab at the University of Arizona, #1 in astronomical research in the US and one of the premier telescope mirror facilities in the world. We got there at 12:45 and they opened up the door for anyone who needed to go to the bathroom right before the tour. Funny - 10 men and 2 women went. Usually it’s the women who have to wait in line. This time, it was the men.

The hour of classroom explanation and the 3/4 hour of actual tour was fascinating - much more so that we had expected. No one in our group was even an amateur astronomer and our guide’s presentation was such that we could all understand it. Because telescopes and the mirrors that make them work are so expensive, they are a collaborative effort. for example one they built here was financed 10 ways:

        25%                University of Arizona

        25%                Germany

        25%                Italy

        12.5%             Ohio University

        12.5%             6 other universities.

And, each one can use the telescope for the percentage of time that they paid for. Thus, there is no secrecy behind them and we could take any pictures or movies that we wanted in the lab.
Here’s some history: In 1608 the first telescope was invented but it was pretty limited and was only like what a Captain of a ship used to see other ships.

In 1609 Galileo wrote a letter to the Prince of Venice telling him that he could build a telescope that would enable the Prince to see what ships were coming in to shore sooner than anyone else: whether they be trading ships with goods or enemy war ships.
In 1668 Newton built mirrors for telescopes that became the standard. The top part of the writing in the middle of this slide that our guide showed us is Galileo’s where he is advertising his telescope and on the bottom is when he is discovering that Saturn has 4 moon.
The bigger the mirror, the better the resolution, the more you can see. And, the University of Arizona, here at this lab are building the world’s biggest telescope incorporating 7 mirrors 8m in diameter, the GMT, or the Giant Magellan Telescope.
Below is a picture of it showing its size compared to a man standing in front. So far they’ve made about 3 of those 7 mirrors and soon they will set those up for at least a partial telescope. These mirrors will be 8’ in diameter with each one shaped as a parabola. The 7 mirrors combined are also shaped as a huge parabola - considered the best shape for a telescope.
Here at Arizona, Roger Angel worked to build a bigger and bigger mirror. He began at home using custard cups until his wife told him that hie needed to take his experiments elsewhere. He found an empty Jewish synagogue to use. One of his first projects was for the Vatican. An Angel building a Vatican telescope in a Jewish synagogue. Cool.

After our guide’s presentation we walked out into the lab itself.

How they make these large telescope mirrors is way above my pay grade but - here’s my layman’s explanation of what they’re doing. And, believe me, I am a layman.

An 8m x 2m cylinder of glass/mirror would weigh a lot and be too cumbersome to deal with. They needed to make it much lighter. They begin with a base shown here in the photo. This base needs to withstand the > 2000 degree temps that the mirror will be heated.
Then they wrap it with steel plates.
Next they fill this with 6-sided silicon cubes to fill this 8m diameter cylinder.

Here’s a picture looking down on the honeycomb design with the ceramic cores in place. The molten glass will now flow between them.
Then they arrange lots of specially designed glass on top in a parabolic shape - thicker on the outside, thinner in the middle.

Finally, they put the ‘oven’ on top of the whole structure.
They seal it and then begin to heat it up over 5 days to a peak temperature of 2130° to melt the glass to a consistency of honey so that the glass melts and fills the spaces between the silicon hexagons.
Meanwhile the whole structure is spinning at a speed of 5 rpm so that centrifugal force and gravity will cause the melted glass to form the correct parabolic shape.

The oven is then cooled to 990° during the next 4 days. Over the next 40 days the whole structure is cooled to 840° and then over the next 66 days it is cooled to room temperature. The ‘oven’ is opened, the structure is put on edge and the silicon hexagons are hosed down and washed out.
Voila - you’ve got a honeycomb mirror than weighs 80% of what it would weigh if it were total glass.
Voila, you’ve got a huge piece of glass but, since it is honeycombed, it will not be as heavy as a huge piece of glass. Ha, ha.

Now you need to put a thin sliver of aluminum on it and polish it to a fare-thee-well. Pretty simple, huh? Here’s the polisher which is entirely run by electronics.
Got that? It’s a pretty spectacular process. Now you know all I know - nah, I don’t want to sell you short. However, even though I might not understand all the physics of the process, I certainly appreciate how intricate it is and what it will enable astronomers to do.

Neither Gary nor I have any experience with astronomy, nor do we own telescopes, but we would certainly recommend the Caris mirror lab to you to see this for yourself. Very cool.

Afterward we walked around the campus to see the original observatory.

We only saw it by accident since it is pretty well tucked away behind lots of other buildings.
Afterward we walked through the Campus town area and found the 4th Avenue Street Fair which runs this weekend.
On our way back we found the Baskin Robbins. Perfect ending.

We’ve seen craftsmanship of many different forms today, from old cars lovingly restored to telescope mirrors scientifically engineered to home crafts artistically designed to ice cream exquisitely whipped. Hmmm, maybe I’ve gone too far here.

‘Change is inevitable, except from vending machines.’


  1. Hi, there, Marleentje, glad you're enjoying the blog. I'm working on your comment problem. This is a test.

  2. And, another test commenting as 'Anonymous'.

  3. On the test above, I did have to check the box that says 'I am not a robot' and then had to click on the 'publish' button again.

  4. on the test above I commented as Nancy Ferguson and did not have to check the 'robot box. This time I'll comment as anonymous.

  5. It seems that when I comment as 'Anonymous' I have to check the robot box and then have to click on 'publish' again. When I comment as Nancy Ferguson I do not have to do either. I just click on the publish box once.