Cool Stars 14 - Submitted Abstract # 200 This version created on 05 October 2006 Preparing for Kepler: Understanding Solar Microvariability Kurt Soto, UC Santa Barbara Gibor Basri, UC Berkeley Francisco Ramos-Stierle, UC Berkeley Tristan Lewis, UC Berkeley Ansgar Reiners, MPI für Sonnensystemforschung The key to understanding total stellar irradiance variability is understanding the mechanisms by which continuum contrast is affected by magnetic flux. The MDI instrument on the SOHO satellite has obtained magnetograms along with contemporaneous continuum images throughout Solar Cycle 23. These pairs of images can be used to study the correlation of brightness with field over the entire disk. To properly study these effects, MDI magnetograms must be corrected for geometrical effects near the limb. We derive the correction by assuming that the distribution of true magnetic flux in the active latitudes should not depend on viewing angle. We examine a series of 106 image pairs from 2001, using both annular rings at various limb angles, and following individual active regions over their full disk passage. We are able to find a simple law which successfully corrects the magnetograms over the full disk (a big improvement over the naive correction by 1/mu). The relationship between continuum images (with limb darkening removed) and contemporaneous corrected magnetograms at all limb angles is used to produce a 3rd-order polynomial surface of continuum contrast vs. magnetic flux and disk position (similar to the approach of Ortiz et al. 2002, A&A 388, 1036). We show how well this procedure reproduces actual solar features. This methodology is useful for predicting stellar microvariability, given assumed magnetic configurations, or attempting the inverse problem. ----------------------------------