RE: [ATM] Ball bearing for triangles

["lou krajci" <loukrajci@comcast.net>]

>From: A. Suijkerbuijk [mailto:a.suykerbuyk@wxs.nl]

>...What interests me most is: can the cooling of a mirror be
>predicted? Is there a certain balance between back and front side?

It depends on the environment your telescope is in.  Is your telescope
always in the same thermal environment?  If yes, and you can measure and
characterize the environment sufficiently well...then you should be able to
come up with a reasonable model.

If you are always in the same environment...then just measure temperature
differences a few times, a few nights, at various times...and you'll have an
empirical model.

>The program "cool" uses just the thickness of the mirror, which puzzles me.
>I would say two mirrors of the same thickness have not the same cooling
>rate, the larger one will cool faster. In other words: numbers like surface
>and volume of the mirror play a certain role.

In this case an assumption is made.  We assume that the mirror
radiates/absorbs its heat only from the front and back faces, not the
side/edge.  For large/thin mirrors this is an acceptable assumption because
the amount of surface area devoted to the side/edge is a small fraction of
the  surface area of the front/back faces.  For small/thick mirrors this
assumption is not so good.

I hope this helps.

Tom Krajci
Albuquerque, New Mexico

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