The Photoelectric Spectroheliometer On ATM

The Harvard College Observatory instrument on the Apollo Telescope Mount (ATM) is a photoelectric spectroheliometer designed to obtain up to seven simultaneouA spectrohRliograms in the range 280 Å to 1340 Å with a spatial resolution of 5 arc sec as well as spectral scans with a resolution of 1.6 Å over the same wavelength range. Because of its large size, this in-strument has a sensitivity far greater than that of any photoelectric extreme ultraviolet (EUV) spectroheliometer flown to date. The instrument has operated correctly since 29 May 1973 and has obtained many thousands of spatial and spectral scans of a variety of solar features. Furthermore, the laboratory photometric calibration has been reestablished in orbit by comparing the response with that of more recently calibrated spectroheliometers flown on sounding rockets in August and December 1973.