I forget the exact number, but the clear night sky is equivalent to a very cold black body radiator, around -30C or so (can't recall the actual value and it pro

I forget the exact number, but the clear night sky is equivalent to a very cold black body radiator, around -30C or so (can't recall the actual value and it probably depends on local temperature too). Radiative equilibrium with it will push your temperature way down. This is the main reason why it suddenly gets so cold at night. From a radiative perspective, you might as well be facing a ceiling of Arctic ice above you. I'm an amateur astronomer. When I do observations at night, I always add an extra layer of clothing. It's amazing just how really cold it gets when all you do is sit under the clear night sky. When it's cloudy it's different. The chill effect due to the (lack of) radiation is much less intense.