Hence it is obvious that if we know the temperature and the integral
humidity as functions of the altitude, we can calculate the radiation of the atmosphere at different altitudes, provided that the relation between radiation, temperature, and humidity is also known.
In 1896, noting that moonlight had to pass through more atmosphere when the Moon was lower in the sky (a nice paradox to entertain grade schoolers with), Swedish Nobelist Svante Arrhenius used the recently invented Langley bolometer to plot IR from the
Moon as a function of its altitude.
Now to answer your question, -LSB-[«But there is a normal atmospheric lapse rate, by which temperature tends to decrease
as a function of altitude.