Telescope (Big Professional Kind)

[Astronuc]

I looked for a thread that had something about history and some information on large telescopes, and didn't find one.  So here it is.

The word "telescope" (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') usually refers to optical telescopes, but there are telescopes for most of the spectrum of electromagnetic radiation and for other signal types.

http://en.wikipedia.org/wiki/Telescope

 

[Retrospector]

I think there's quite a lot of interesting history regarding the big telescopes, such as those at Mt. Wilson and Palomar. The one at Palomar was the key instrument in faint object astronomy for a long time before the Hubble Space Telescope in space and massive instruments in places like Hawaii came along. Optical fabrication has grown by leaps and bounds in recent decades. I think I read somewhere that the glass disk used to make the mirror for Palomar too a year or so to cool (glass has rotten thermal conductivity.) Don't quote me on that number though! These days fabrication methods have grown much more sophisticated.

[Skyjim]

Also, you have to carefully cool a slab of Pyrex like the 200 inch mirror blank - most of the cooling time was actually in a annealing oven.  If you simply took it into ambient temperature after pouring, the blank would develop major cracks. Eight months were spent annealing and cooling.

The pouring of the mirror for the 200 inch was quite an adventure.  First attempt failed as the firebrick forms for the honeycomb design on the back of the mold broke loose and floated to the surface...

A pretty good condensed account here:

http://www.americanheritage.com/articles/magazine/it/1985/1/1985_1_12.shtml

Jim