QUESTION:
Is there any protective covering between the telescope and the sky?

ANSWER from Terry Richardson on October 17, 1995:
I'm not sure if you mean a protective coating on the actual surface of the 
mirror, or if you mean between the telescope and the sky.
 
I will answer both questions for you, starting with the protective coating
on the primary mirror of the telescope. The main mirror (primary) of the
telescope has a silicon monoxide over-coating which protects the surface of
the mirror from dust and contamination. 

As for the other part of this question, there is nothing between the 
telescope and the sky (nothing protective anyway). 

I hope this answers your question, 
Thanks for writing.

Terry Richardson