I noticed a very curious thing on the weekend. On two consecutive nights, the temperature had fallen to just above freezing. Dew wetting everything. But the secondary mirror of my 17.5" dob was frosted over! The secondary's holder is all metal, painted black & hollow, & filled with a dew heating strap that was NOT ON. I just cannot understand how this secondary mirror could frost over???
Anyone have an idea as to why, please?
I can only think that the metal casing is acting like some sort of heat sink where the atmosphere is pulling out heat.
AND, I've also noticed up at Katoomba Airfield, black surfaces actually having dew form on them, regardless of the material be it metal, vinyl padded seat, whatever, just black, yet no other surface had dew form on it, including metal ones, even bare metal.
Why is it so???
Mental.