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31 August 2001
UK SAS Members Begin Work on 42" Telescope
by Steve Taylor
Fellow SAS members might be interested to hear of the project of which I am Technical Director. The Astronomy Centre is a UK based group of amateur astronomers who have been working for close to 20 years on creating a top-class telescope facility for amateurs to use. Despite some fallow periods, close to ten years of zero and even negative progress, we are now pushing ahead very quickly on many fronts. Members have dedicated huge amounts of time and not a little amount of hard cash to building a large observatory building to house an instrument now specified as a 42" reflecting telescope operating at F4. We have some other instrumentation already, including a 30" and a 17" instrument as well as 12" reflecting BINOCULAR telescope, the largest pair of binoculars most of us have ever seen! Coming reasonably soon is a spectrohelioscope (based on old Amateur Scientist articles) and of course ultimately all our equipment will be available over the net.
The big catch is that WE will be making the mirror for the 42" scope and the early stages of the project are now well under way. Last Monday, we took delivery of the glass blank specially made in Canada for us in a fairly exotic material, a modified glass, heat treated to give it extremely low thermal expansivity and high stiffness. The material is in some ways only slightly inferior to fused quartz. As you can see one odd property of the glass is that it is opaque and black.
If you take a look at our website (http://www.astronomycentre.org.uk), you can see some pictures of the glass blank (and the technical team working on the project too!). Please take a look at the rest of the work we have been doing too. A 30 foot diameter dome, with doors 30 feet long, all built by a team of eight people; a building with no roof and floors rotted out restored by the same team.
We will be taking very cautious steps to learn how to handle the glass very soon. To much laughter, we cast a CONCRETE "mirror", of identical weight and dimensions as the $8,000 blank this week, as a test piece to work on handling procedures. When we cast the "mirror", the sheer scale of our project suddenly hit us all.....The dummy mirror weighs close to 250 pounds, and there is an awful difference to seeing a line 42" long and a surface 42" in diameter !
To give some idea of the scale of our problem, for non astronomers/telescope builders, by our reckoning, if the mirror was as wide as the ocean between the Uk and the USA, the maximum "wave height" we want on the surface is just 1.5 feet !
I hope to be able to post periodic updates on the instrument's construction to the SAS newsletter.
