Rocket twilight observations of H I 1216 A horizon brightening near 150 kilometers

Two rocket observations of Ly α with a solar zenith angle of 120° indicated that the ratio of the brightness near the solar horizon to that near the zenith and antisolar points was 1.6±0.2 and 1.8±0.2, respectively. The first was predawn and the second post sunset. In the second observation, the brightness close to the antisolar direction varied less than 15% between 135 and 105 km. These phenomena are consistent with geocoronal models of multiple scattering of solar Ly α radiation.