Absolute solar flux measurement shortward of 575 Å

A rare‐gas ionization chamber was used to obtain an accurate measurement of the absolute solar EUV flux in the 50‐ to 575‐Å region. The instrument, operating in total and near‐total absorption, was flown on a solar‐pointing sounding rocket on August 16, 1983. For the day of the flight the solar activity indices were F10.7 = 132.1 and RI = 80, and the integrated solar irradiance at the earth, corrected for atmospheric absorption, was found to be 4.31 ± 0.31×1010 photons cm−2 s−1. Almost exactly a year earlier (August 10, 1982) the same instrument measured an integrated solar flux of 5.71 ± 0.42×1010 photons cm−2 s−1 during a time of enhanced solar activity (F10.7 = 209.5 and RI = 155).