Recent analyses carried out on spacecraft total solar irradiance measurements have shown quite convincingly the importance of faculae in active regions and network for irradiance variation over the solar cycle. Also, infrared photometry of faculae places new constraints on the mechanisms responsible for heating in these magnetic structures. One element of the program funded here consists of accurate photometric observations in the infrared to enable a study of the deepest layers in the structures in more detail. Comparison of the results with mhd models of facular and sunspot flux tubes should be a powerful new diagnostic of the mechanisms that lead to facular excess brightness. A second aim is to evaluate the contribution of active region and network faculae to total irradiance over the solar cycle. It is intended to use photospheric distribution obtained from archival KPNO magnetograms, and an empirical relation between their magnetic flux and contrast that will be derived through photometry in the visible and near IR. The results of these studies should considerably advance understanding of solar luminosity modulation mechanisms and their relation to photospheric magnetic activity. The overall aim is to understand solar luminosity variations as they might apply to terrestrial changes (eg. climate). Proxy data might permit reconstruction of solar history in the recent past.
