Molecular oxygen photoabsorption cross sections have been measured at 0.3-¿ intervals between 1214.0 and 1218.6¿ at temperatures of 294, 195 and 82 K. The measured pressure dependence of the cross sections is in satisfactory agreement with earlier observations, but the room temperature cross sections are found to be significantly different from previously reported high-resolution measurments in the Lyman &agr; window. At the lower temperatures the shape of the cross section curve changes, and the cross sections near the absorption minimum are found to be substantially less than at room temperatures. The application of these results to the analysis of rocket measurements of the extinction of solar Lyman &agr; radiation in the atmosphere is discussed, and it is shown that it is essential to take into account both the temperature and the wavelength dependence of the molecular oxygen photoabsorption cross section if reliable oxygen concentrations are to be deduced from the rocket measurements.