On Sat, 29 Nov 2014 22:55:50 +0000 (GMT), "Dave Liquorice"
wrote:

A clear night sky is at around -40 C. Thermo dynamics mean that the
different temperatures try to equalise but space is a bit big and
there isn't enough heat in the screen to warm up space. So the screen
just radiates heat into space and cools and cools and cools...

Was trying to see how the windscreen would be below air temp, but I
had neglected the radiation component. Doh.