The use of the moon as a standard gauge by recording Baily's beads caused by the topography near the moon's rim requires the precise knowledge of the lunar limb. The observation of stellar occultations can refine the lunar profile better than any astronautic exploration, yet. Especially grazing occultations steadily improve the precision of the lunar profile in its polar regions. The MOONLIMB project of IOTA-ES (by D. Büttner) incorporates the data of lunar occultations into a new database of the lunar limb profile.

Due to librations the lunar profile periodically changes. But during a solar eclipse the libration in latitude is always close to zero, while the longitude libration may have any value. Therefore the projected outline of the polar regions of the moon only slightly varies, while other regions may completely alter their appearance. This strongly preferes the polar regions for the analysis of the solar diameter.

During a total or anular sun eclipse, the moon's polar regions are projected on the edges of the eclipse path. Another advantage is the slow proceeding of bead phenomena along the edge of this track. Besides the less accurate knowledge of the lunar profile far from the poles, Baily's beads observed from deep inside the eclipse path develop too rapidly for a sufficient time resolution. Any observer who records thoroughly timed Baily's beads from the edges of an eclipse path with video equipment can gain valuable data and contribute to the knowledge about the variability of the sun's dimensions.

For more informations please contact Konrad Guhl.