Height of the Twilight Sodium Layer: Evening–Morning Effect observed at Victoria, British Columbia, from February 1967 to February 1968

Abstract

AN interesting variation in the height of maximum density of the twilight sodium layer was observed at Victoria, British Columbia, during a year long series of observations, between February 4, 1967, and February 29, 1968, using a birefringent photometer directed towards the zenith sky. It has been found that, in general, the height of the sodium layer during the morning twilight period is lower than the evening twilight layer by an amount which varies throughout the year. The difference in height appears to be greatest around the times of the equinoxes amounting to approximately 5 km, and least near the solstices, when the difference diminishes to zero.