Variation in the nocturnal radiation from the sky with zenith distance and with time during the night

Abstract

The hourly variation of the heat radiation coming from different altitudes of the night sky was measured on three nights in April and May 1936 with a Moll’s Micro-galvanometer anda Micro-thermopile provided with a small aperture. These observations show that the nocturnal cooling of the radiating air layers as shown by the decrease in the equivalent black body temperature of the sky is maximum for altitude zero (i.e., horizontal) and minimuni for altitude 90° (i.e., zenith). The authors have great pleasure in thanking the Director-General of Observatories for providing necessary facilities for the investigation.