An evaluation of the sky Lyman alpha emission in International Ultraviolet Explorer (IUE) spectra

An emission line at 1216 A is noticeable in International Ultraviolet Explorer spectra for exposure times longer than about 5 minutes in low dispersion. For a set of seven sky-only spectra the expected Lyman alpha column emission rate was calculated from standard models of geocoronal and interplanetary hydrogen. The geocorona contributes between 5% and 50% of the signal, depending on the observing geometry. The calculated emission rates are higher than the observed ones by approximately 19% with a scatter of 11%. This discrepancy is smaller than the combined errors of observation and calculation.