188 Alaskan Science Conference 



auroral zone. Hence Alaska is an exceptionally favored region 

 for the study of these variations. The measurements of signal 

 behavior at College reveal definite correlation with magnetic 

 (and hence auroral) activity. Such correlations are being made 

 and in the future will become a more significant part of the 

 activity at College. 



Auroral Heights 



Beginning in 1948-49 the National Bureau of Standards pro- 

 vided for the resumption of auroral height determinations as 

 part of its general ionosphere program. The old cameras used 

 in the Polar Year were used at the previous locations. These 

 manually controlled cameras were replaced after the first season 

 by automatic, unattended K-24 cameras (coated optics, f/2.5; 

 exposure 50 seconds) operated by a radio link between the 

 camera stations which are 7.6 kilometers apart. The heights 

 determined for all types of aurora vary from 50 to 250 kilome- 

 ters with a mean at 116. 



Intensity of the Light of the Night Sky 



The light of the night sky at College, Alaska, usually includes 

 the aurora in addition to the airglow, zodiacal light, starlight 

 and light from the milky way. Measurements of the illumina- 

 tion of the night sky at College have been made from time to 

 time and will be continued through this winter. Early efforts 

 were made during the winters of 1941 through 1946, first by 

 means of a visual photometer, and later by means of photo- 

 graphs of the zenith at 2.5 minute intervals. The earliest meas- 

 urements with the visual photometer were difficult to make 

 and therefore crude. The equipment was cumbersome. Meas- 

 urements made later in this period were made on the equipment 

 modified by the introduction of comparison wedges and by the 

 careful control of processing. Even with these changes it took 

 one man's full-time efforts for 18 months to analyze six months' 

 film. 



In recent years the measurements of the intensity of the light 

 of the night sky have been revived. The measurements are 



