Thursday, April 9, 2015

The Mirror Lab

Image result for very large array
Very Large
Did you ever wonder how and where the extremely large mirrors used in telescopes, like these in the Very Large Array in New Mexico, are made?  How about the ones for the Giant Magellan Telescope, coming soon to the Chilean Andes?  How do they move them?  Aren't they worried about breakage?

I had all those questions and more before I toured the UofA's Steward Observatory's Mirror Lab. Free thirty minute tours were offered to those lucky enough to secure tickets at the Festival of Books; I received the very last one available.... at 9:30 in the morning for a Festival which didn't open until 10.
This was a hot commodity, and I was thrilled to be able to join the party.

High in the sky so that ambient (man-made) light is not a factor, in an area with little to no rain or geologic disturbances.... or people, for that matter, the world's largest telescope will be created by linking seven ginormous mirrors which will collect images at 10x the resolution of the Hubble Telescope.

This is the model.
Three of the mirrors have already been cast.
They are working on the rest.
It's not a simple process.
Those parabolas are 27' in diameter.

They melt glass 
by loading it into a honeycomb mold
the sections of which are secured beneath those silver fastenings and covered with the foam.
It takes almost three weeks for the furnace on which it sits to reach the peak temperature of 1165 C (2129 F).  The glass spins and melts and then spins some more and cools.

It's lifted by a very cool machine which is fixed to the mirror itself by very strong silicone rubber sealant
The mirror is tilted and placed in the turning ring and then sent to the Large Polishing Machine.
You couldn't make this stuff up.
I guess the creativity goes into the engineering and not the naming.

The mirror sits in that white tray and is polished with two diamond polishers which lap one another, creating the offaxis optical surface with an accuracy of about 10 ┬Ám rms.(

That's very very exact.  Because there will be seven mirrors in need of synchronization,  the slightest variation between the Mirror Lab's creations will cause massive distortions.  
It's a gigantic project of infinitely small details.
Where is it happening?  
Underneath the football stadium at the University of Arizona.
How do they move it from Tucson to the Las Campanas Observatory in Chile?
Specially designed trucks back up to the Observatory in the middle of the night.
Once they are loaded, the mirrors are accompanied by a brigade of flashing lights as the highway is closed down.  The thing is too big for just one lane, or two lanes.  It can't be jostled or bumped or caught in a multi-car collision.  So, they close the road.
The mirror is loaded onto a ship, floated to Chile, and put on another truck to travel to the Atacama Desert.

And it all starts here, in my home town.


  1. WOW! That's mega-cool! I guess we take for granted that things like this just appear and don't understand all of the logistics that go into such a detailed telescope. I'm totally gob-smacked!

    Thanks for sharing with us and the pictures.

    Megan xxx

    1. It was amazing! I agree with you; we think things just appear without considering the origins. I, too, was gob-smacked (one of my favorite words!)


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