Mxsmanic opined

Ash Wyllie writes:

Actually, it can. I have seen frost on metal surfaces (like wings) when the
air temp is above freezing.

What was the temperature profile of the air during the preceding
hours, and at the exact time of the observation?

If the air is warming up and moist, metal surfaces might well be below
that temperature and below the dew point.

It was before dawn, and the temp had dropped over night (and was still dropping).

A clear night sky is /cold./

Yes, because large masses of water vapor have a moderating effect on
temperature, making warm days cooler and cold days warmer.

Look up _radiational cooling_ . Space is in the single digits absolute, and
the atmosphere is pretty much transparent to radiation. Objects will radiate
energy trying to heat up interstellar space, and cool in the process.

You might drop in on some of the amatuer telescope groups. They have the same problem.


-ash
Cthulhu in 2005!
Why wait for nature?