Optical investigations of the moon and spectrophotometric standards

Spectral and photometric base data are presented for two lunar areas recommended as standards for exoatmospheric spectrographic measurements. Ground-based observations of the Plato and Le Monnier lunar crater regions have been made in the wavelength range 3225-7475 A during different phases. Normalized brightness factors have been determined, together with the phase dependence of the color index of the craters. Increases in the steepness of the spectral curve with phase angle were found to occur at a rate of 0.20% per deg for the B(0.56 micron)/B(0.40 micron) index, and 0.15% per deg for the B(0.70 micron)/B(0.56 micron) ratio.