If you have access to a psychrometric chart, you can plot the dry bulb and wet
bulb temperatures, and then determine the surface temperature of your telescope
(probably close to the dry bulb). If the scope's surface temperature is below
the dry bulb / wet bulb temperature intersection on the chart, you'll probably
have dew form. That is the method we used in air conditioning design procedures
to determine an ideal coil temperature for a given set of cooling conditions.
Cave Creek, AZ
Brilliant Sky Observatory
Dedicated to speckle interferometry of close double stars…
[mailto:az-observing-bounce@xxxxxxxxxxxxx] On Behalf Of Paul Lind
Sent: Wednesday, January 18, 2017 1:31 PM
Subject: [AZ-Observing] Predicting Dew
This morning I noticed large amount of dew on things in my yard, reminding me
of observing sessions that were ruined by severe dew. I'm talking about puddles
of water on my observing table and water dripping off my scope.
So, my question is this: Is there a way to predict dewing from the
Clear-Sky-Charts and other data, say, by comparing transparency, humidity, and
temperature? The air-temperature/dewpoint relationship is not a good indicator
of dewing because radiative cooling from a clear sky can cool objects well
below both the air temperature and dewpoint. It's a good predictor of fog.
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