Re: [ATM] New home built 12" ultralight dob

[Mark Holm <mdholm@telerama.com>]

Per work done by Alan Adler and Brian Greer, reported in Sky and 
Telescope, the best place for a fan is blowing horizontally, across the 
front of the mirror.  This not only cools the mirror effectively, but 
also breaks up the boundary layer that causes that swimmy effect.

Slow swimming is probably the result of warm air rising off of the 
mirror, unless you were observing on a very still night.  Your 
observations are in exact agreement with Adlers.  He found that a front 
blowing fan could clear away that swimmy effect in about 5 seconds!

References for Adler and Greer's work are at 
http://www.atmsite.org/contrib/Holm/yolo/index.html
Scroll the index to the bottom and click the link "Links".  Scroll to 
the bottom of that page for the ventilation references.

-- 
Mark Holm
mdholm@telerama.com


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