I was fortunate enough to be at the Sewell Mirror Lab on the day that the glass melted for the first off-axis segment for the GMT. VERY cool process and incredible technology to make the mirror both strong and light. They put ceramic hexagonal "rods" in the oven and put he raw glass (in block form) on top of it. They then rotate the oven at the correct speed while heating the glass. The glass melts and forms a shape that is very close to the final shape needed. After the glass cools (which takes months), they remove the rods. They then do their final finishing of the mirror. We also got to see the mirror for the second halve of the large binocular telescope undergoing final testing.

Very cool all around. The main problem is that I couldn't figure out how to get an 8m mirror in my mini-van.

__________________
Clear, Dark Skies

Mark