Substitute material, not glass, for Newtonian type telescope mirror; what would be best?

7 Comments

1. Harold J says:

   April 23, 2010 at 3:47 am

   Diamond has a very strong bond, but any substance can be melted At normal atmospheric pressure, the melting point of diamond is 3550 degrees Celsius (6422 F). It can be done.
2. rpm92 says:

   April 23, 2010 at 4:45 am

   Melted diamond would loose its structure and whilst it would still be carbon, it would not be diamond anymore! Additionally, the high temperature would ignite it if it was heated in air, and the diamond then burn to form CO2 and water. An expensive mistake!
   One option is to use liquid mercury on a rotating platform. The speed of rotation creates a parabolic reflector. Thus speed could be altered to form a desired focal length.
   Even if Hg had too low a boiling point for the application you have in mind, its density is such that a moldable material, like an epoxy resin could be formed on top, the hardened product could then be silvered.
3. mike1942f says:

   April 23, 2010 at 4:58 am

   Telescopes have been made with mirrors of rotating mercury with the obvious problem that it can only point straight up and the mercury vapors are toxic.
   Modern telescope mirrors are made of low expansion Pyrex-type glass (borosilicate) with a relatively thin reflecting surface and a grid of glass cells behind for strength and to allow air conditioning to keep the temperature and thus the curve of the glass under control. They are cast is a huge rotating kiln so the glass surface is already curved, greatly reducing the cooling time and the amount of glass that needs to be ground off to make as perfect a surface as possible. Blanks 8 meters in diameter are made regularly at the Mirror Lab of the University of Arizona http://mirrorlab.as.arizona.edu/
   Almost any other material would either have greater expansion, have a much higher melting point or cost a fortune.
4. claptic says:

   April 23, 2010 at 5:09 am

   Try building your own telescope using mostly aluminum parts with I think pyrex lens. Thermal equilibrium is nearly the same and temperature change becomes less of a factor. You would need to verify what I am saying as quartz may be better in this adaptation.