How long does it take to cool a large mirror being produced for one of the world’s largest astronomical telescopes?


Specific Question:


What I want to know is – how long did it take the mirror to cool off? That's the most amazing part, to me. I just can't get my head around how you let something like that cool properly, so it doesn't warp. It's one of those science-y things that gives me shivers.




From: Phil M. Breidenbach

Date: Jun 3, 2005 9:35 AM

Subject: RE: Subaru Mirror

 I can't tell you actual times, but I do know it was close to a year, if
not longer for the glass to cool down.  They made a furnace at
Corning to do
this job; in fact, I believe they had to build an entire building to make
the blank.  As the glass cooled, it was monitored closely.  After the
process of cooling was finished, it was shipped to
Pittsburgh where the
grinding and polishing process started.  This removed any excessive warpage
that might have happened during the cool-down process. I believe during the
final polishing processes, they had the blank on the active support
structure to mimic the final resting place of the mirror. This also helped
to avoid any flexing or distortion.

   I hope this helped a bit.  I envy anyone that has the opportunity to use
the telescope in any way!

   Have a good day!

Phil Breidenbach
member: Amateur Astronomers Association of Pittsburgh
             North Hills Amateur Radio Club
Active: reader, bibliophile and bicycle rider


For more information, or a clarification, send your request to the following electronic mail 
                  < >.
Editor’s Note: This Science question was answered by a very experienced amateur astronomer, named
Phil M. Breidenbach, who also is involved in amateur radio (call sign: AB3AW). Mr. Breidenbach is 
employed with the Brashear Division of L-3 Communications. The Brashear Division, located in 
Pittsburgh, is a direct descendent of the original John A. Brashear Company, which, beginning in
the late nineteenth century, was known for the production of high quality optical and scientific 
The immediate corporate predecessor to the Brashear Division of L-3 Communications, Brashear L.P., 
grinded and polished the large mirror for the 8.2 meter Subaru Telescope, of the National 
Astronomical Observatory of Japan. This telescope is located on the summit of Mauna Kea, a
dormant volcano on the Big Island of Hawaii. The Subaru Telescope started scientific observations
in January of 1999.
Glenn A. Walsh, Author and Editor of History Web Sites on the Internet:
Electronic Mail - < >
* Buhl Planetarium, Pittsburgh: 
  < > 
* Adler Planetarium, Chicago: 
  < >
* Astronomer & Optician John A. Brashear: 
  < > 
* Andrew Carnegie & Carnegie Libraries: 
  < > 
* Duquesne Incline cable-car railway, Pittsburgh: 
  < >