The 10-Micron Limb Darkening of Venus

In June 1964, several diametric profiles of the 8to 14-/z flux from Venus were obtained with the 200-inch Hale telescope operated in the east-arm Cassegrainian mode. These data were recorded with a photometer system described previously [Westphal et al., 1963] as part of a surveillance program [Westphal et al., 1965]. Venus was near inferior conjunction and 52.2 sec of arc in apparent diameter, close to the maximum angular size accessible with the 200inch telescope. Monitor photographs taken during the recording of the data were used to check the exact positioning of the scans on the apparent disk. These photographs also allow an estimate of the seeing disk in the visible to be made and, by a technique to be described below, an estimate of the instrumental spatial response function. An estimate of the true flux distribution along the profile was made by