[bmitc]

> The AIM-9X is infrared imaging based rather than heat signature based.

Isn't heat detected by infrared? What's the difference?

[Sharlin]

Cloudless sky is cold, and at 30,000 feet extremely cold. Anything not-sky is going to contrast against the sky, even if it has no internal heat source (and remember: if it has electric things in it, it produces heat).

[hammock]

Yes warm bodies put off infrared, but so does the sun, and the suns IR rays are reflected by objects just as they are in the visible range. These reflections used for imaging

[aembleton]

The balloon reflects IR, just as it reflects visible light