Measurements of the limb darkening of faculae near the solar limb

Measurements are presented of the contrast at 525 nm of solar faculae. The measurements were obtained using an extreme limb photometer (ELP) in 1975 and 1979 at the San Fernando Observatory. The mean contrast of active regions was determined from the limb inward to 54 arcsec, averaged over an annulus determined using the slits of the ELP. It is found that the contrast of faculae increases with heliocentric angle theta, from mu approximately 0.25 to mu approximately 0.065, where mu is the cosine of theta. The average value of the mean contrast of facular regions is 2.1%, with a possible upper limit of approximately 5% at mu approximately 0.1, determined from regions with the greatest filling factor. When corrected for a filling factor of 10-15%, this mean contrast implies a contrast for individual faculae of 30-50%.