Records of solar activity that describe a Sun “covered with spots” began almost 3000 years ago. The frequency of these “sunspot” observations was greatly enhanced beginning in the early 1600’s with the discovery of the telescope and its subsequent rapid spread throughout Europe. By the 1700 and 1800’s, key scientific discoveries about the physical characteristics of sunspots and their approximate 11-year cycle in number and latitude dependency had been made. In more recent times, scientists have searched for evidence that changes in the Sun’s total energy output (irradiance) have corresponded with changes in the physical features on the surface of the Sun. By the 1980’s, sunspots were shown to “block” a portion of the Sun’s irradiance, which we now know is tempered by bright features on the Sun that increase its total irradiance.
Concurrent observations of solar activity and solar irradiance allow for the development of regression models that link these phenomena and provide an avenue to extend the modeled relationships back to the past using “proxy” indicators of historical solar activity. The Naval Research Laboratory’s (NRL) solar variability model is one such example. In this talk, I discuss the recent evolution of the NRL model estimates of solar irradiance variability between 1610 and present day in context with new, although yet incomplete, understanding of the Sun’s variability.