telescope Warm up

I've heard lots about cool down time but what about warm up time?? Say like moving a dob from an air conditioned house to the great hot/muggy outdoors??

Does it heat up faster than it cools down??


Mark V

That depends on a lot of factors. In general, telescopes conduct, convect, and radiate heat at rates based on color, materials, and design, and warm up would be similarly impacted (thermal inertial). I failed Thermodynamics, but recall that heat energy soaks faster (or at least more efficiently) going from hot to cold depending on the size of the mediums for same delta T's.

There is a tug-of-war between competing thermal effects, including overshoot as outside temps drop (or rise). I use a Radio Shack digital indoor/outdoor temperature meter to see how close the primary optic is to ambient air temp, but they never are equal.

Best not to store optics at cold temps and introduce them to warm, moist air, as this can cause other problems (dew).

A cooling-down mirror has two problems:

1) heat waves rising off the face of the mirror
2) shape-changing of the mirror due to different parts of the mirror cooling at different rates (center vs. edge, etc.)

A warming-up mirror has the second problem, but not the first, since cooled air from the mirror will be sinking off the backside instead of rising in front. You will still get wavefront distortion from the mirror being the wrong 'shape' while it's equilibriating.