text: Radiative cooling is commonly experienced on cloudless nights, when heat is radiated into outer space from Earth's surface, or from the skin of a human observer. The effect is well-known among amateur astronomers.
  The effect can be experienced by comparing skin temperature from looking straight up into a cloudless night sky for several seconds, to that after placing a sheet of paper between the face and the sky. Since outer space radiates at about a temperature of , and the sheet of paper radiates at about  (around room temperature), the sheet of paper radiates more heat to the face than does the darkened cosmos. The effect is blunted by Earth's surrounding atmosphere, and particularly the water vapor it contains, so the apparent temperature of the sky is far warmer than outer space. The sheet does not block the cold, but instead reflects heat to the face and radiates the heat of the face that it just absorbed.
  The same radiative cooling mechanism can cause frost or black ice to form on surfaces exposed to the clear night sky, even when the ambient temperature does not fall below freezing.