Solar variability observed through changes in solar limb-darkening function and mean diameter. Final report, February 1, 1987--August 31, 1993

The advantages of a dedicated, ground-based observatory over measurements from spacecraft are its relative adaptability, ease of maintenance, and low cost. However, groundbased observations must contend with problems introduced by observing through the Ear-th`s atmosphere and by changes in the long-term stability of the observing instrument. Both of these problems have been addressed at SCLERA and currently pose no limitation of solar diameter measurements at the parts-per-n-tillion level. The atmospheric problems of seeing and differential refraction are managed by separate procedures. For the former, a technique is used for the definition of the edge of a solar limb which exhibits a greatly reduced sensitivity to atmospheric seeing (Hill, Stebbins, and Oleson 1975). For the latter, diameters measured at several solar latitudes are used to yield a solar oblateness and diameter with reduced sensitivity to differential refraction. Differential radius measurements are used to detect changes in the solar limb-darkening function with a reduced sensitivity to differential refraction. The long-term stability of the telescope is monitored with an interferometric technique which is itself stable over long periods of time. Exploration of information contained in the global oscillations of the Sun is the basis of solar seismology programs. Such exploration permits the examination of the internal structure of a star at an unprecedented level of detail and accuracy. Changes in the internal structure of the Sun relevant to changes in energy output can be detected through observing changes in the mode frequency of oscillation. This approach is also used at SCLERA in its study of long-term variability in solar irradiance