Solar Variability and Climate: The Balloon-Borne Solar Disk Sextant

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This project will examine the solar diameter at different orientations. A series of past balloon flights of the SDS have demonstrated its ability to measure solar diameters with a precision (rms residuals) at a given orientation of 14 milli arc s for individual measurements. In the present configuration we make approximately 5 measurements per second. Design features of the latest version of the instrument insure that this same precision will be retained at different orientations, and from year to year. The primary objective of these flights is to obtain the relationship between diameter and luminosity changes. When combined with historical diameter data, the relationship will allow the determination of the magnitude (or, at least, upper limits) of the solar luminosity changes for nearly the past three centuries. This information will be provided to climate modelers in order to elucidate the effect of solar variability on climate change. A secondary objective of this project is to obtain a high precision value of the solar oblateness for each flight, and thus test whether it changes with time as recently suggested by other researchers. The five year term of the proposal has two purposes. First, these flights, when combined with the flight recently carried out, will cover over half of a solar activity cycle, and thus provide a meaningful test for variability. Second, according to current plans, the EUDOSSO experiment (a derivative of the SDS) should fly on the ESA mission EURECA 3 in 1997. The present results will provide an invaluable data base for EUDOSSO, and one flight overlap will allow an intercalibration of the results. # //