The investigators will explore the possibility that there are systematic changes in the diameter of the sun on timescales ranging from years to centuries. Such changes, and their consequent effect on total solar irradiance, can affect weather and/or climate. The main effort is to conduct a detailed analysis of data obtained on flights of the Solar Disk Sextant, a balloon borne instrument first operated in 1992. Analysis of individual flights has demonstrated that the instrument is capable of measuring the solar diameter to the required precision of one part in 100,000, but systematic effects have to date resulted in flight to flight variations much larger than this. In the present project, the principal investigator will work in collaboration with experts on the calibration of optical astronomical instruments to understand and correct for the systematic effects in past data. If this effort is successful, more flights of the payload will be made in collaboration with the NASA Goddard Space Flight Center.
