Lyman α scattering in the Earth's hydrogen geocorona: 2.

Analysis of experiments bearing on Lyman α excitation in the night glow leaves two possible explanations. One is a combination of direct scattering in a distant hydrogen cloud following the earth and multiple scattering in the thermosphere and exosphere. There is a difficulty accounting for the presence of the hydrogen cloud or geocoma. The other explanation is that during the night the thermosphere and exosphere contain 4 to 5 times as much hydrogen per unit column above 120 km as during the day. Although considerably more hydrogen is expected at night because of the much lower temperature, it is questionable whether a large enough change can occur in half a day.