MadSci Network: Physics

Subject: How can I predict when dew will form on a corrector plate.

Date: Thu Dec 23 18:43:42 2004
Posted by Howard C. Anderson
Grade level: grad (science) School: No school entered.
City: Tempe State/Province: AZ Country: USA
Area of science: Physics
ID: 1103849022.Ph

Schmidt-cassegrain telescope.  Corrector plate collects dew under certain
conditions.  I read the posted article re dew.  Corrector plate radiates to 3
degree Kelvin sky.  Air molecules contribute air temperature heating to outside
of corrector plate.  Inside telescope, walls of telescope conduct heat from
outside, warming the air molecules which transfer heat by conduction to the
inside of the corrector plate.  Air inside also presumably radiates heat through
the corrector plate. Assuming thin steel telescope walls 25 inches in length and
a corrector plate thickness of 3/8 inch and diameter 10 inches, it should be
possible to calculate the surface temperature of the outside of the corrector
plate using the heat equation, the thermal conductivity of steel (.115), air
(.0000568), glass (.002) and the air temperature. (Does the radiative efficiency
of glass also play a part?)  The dew point can then be used to determine
approximately when dew will start forming.  (I think if my old college
professors had thought of this, it would have been on one of my tests.  It is
only at this time of year that this begins to be a problem for me here in
Arizona... See my web site and you will see why it
matters to me.)

Re: How can I predict when dew will form on a corrector plate.

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