Astrogeology maintains the highest quality data on the brightness of the Moon via the Lunar Calibration Program, which provides essential data for many satellite missions. These data are used to calibrate many spaceborne Earth observing instruments, including the OLI (Operational Land Imager) on Landsat 8, and the NASA flagship remote sensing instruments: VIIRS (the Visible Infrared Imaging Radiometer Suite) on Suomi NPP and MODIS (the Moderate Resolution Imaging Spectroradiometer) on Terra and Aqua. Lunar calibration is planned by virtually all future operational satellite missions, including National Oceanic and Atmospheric Administration (NOAA) (GOES-R ABI), NASA (VIIRS on JPSS), the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) (MTG FCI and EPS), and Japanese, Chinese, and Indian meteorological agencies. Consistent calibration is essential for comparing data collected by different instruments over decadal time scales, thus allowing climate and land use changes to be accurately assessed. Lunar calibration provides a reliable method to collect visible and near-infrared data that are consistent through time and comparable across imaging platforms.