High-altitude measurement of the Lyman alpha nightglow at solar minimum

Observations of the geocoronal Lyman α emission rate were obtained as a function of altitude at local midnight near the minimum of solar activity. Solution of the appropriate radiative transfer equations for several hydrogen models, combined with observations of both the solar flux and the extraterrestrial Lyman α background, suggests a reference hydrogen density at 100 km in the range from 6.3×106 to 2×107 cm−3;, with a best estimate of 1.6×107 cm−3. This implies an increase in the hydrogen production rate of nearly a factor of 2 from January 1964 to fall 1967.