1811 T. Adams 107 Our gilded sterns point to the zenith sky.
1938 22 July 8/1 The measurement of the brightness of the light in the zenith sky an hour after sunset and an hour before sunrise made the findings possible.
2001 (Nexis) 16 Dec. 1 d Welbon would rather..recite fluctuations in air pressure or light levels of the zenith sky.