23 April 1965
Vol 148, Issue 3669

About The Cover

The rayed band is an aurora emitted at altitudes above about 100 kilometers when oxygen and nitrogen are bombarded by electrons with energies of several thousands of electron volts. The source of these electrons is not known. The band is a horizontal region of dense luminosity, and the rays are narrow, magnetically vertical columns of light. See page 499. [V. Hessler, College, Alaska]