Results from the Occultation of Regulus by Venus, July 7, 1959.

Teams of observers from the Harvard and Smithsonian Observatories, stationed at Madrid, Le Houga, Merate, Catania, Beirut, Shiraz, and Bloemfontein obtained visual times of ingress and egress of Regulus. Photoelectric light curves at ingress were recorded at Le Houga and Bloemfontein. Analysis of the visual observations, supplemented by published data from six European and two South African stations, has yielded the differential geocentric coordinates of the center of Venus with respect to Regulus on July 7,1959, at 14h24m00s U.T. a (Regulus) -a (Venus) = - 9"1 11 ~0"013 p.e., ~(Regulus) -~(Venus) = -0"342~0"012 p.e. The difference between observed (U.T.) and computed (E.T.) times of mid-eclipse is - 28S.00~0S.40 (p.e.). If U.T. - E.T. - 34s for 1959.5, aprovisional correction to the ephemeris data is 0- C + 6S.0. The radius of the atmospheric shell corresponding to half-intensity was 14"403~0"007 p.e., or, at unit distance, 8"500~0"005 p.e. If the optical radius is 8"41 (ephemeris value), the corresponding altitude Zo is 65 km above the top of the cloud layer. Analysis of the photoelectric observations by the theory of differential refraction yielded the scale height at this altitude H(z0) =RT/mg, and its variation with z in the range Iz-zoi ~20 km, viz., H(z0)=6.8~0.2 p.e. km, and (1/H) (OH/Oz) = +0.010~0.002 p.e. km-1. If the acceleration of gravity is 860 cm sec~2, and the mean molar mass m=42.5 (CO2 =0.90, N2 =0.09,A+ =0.01), then T(z0)=297~10p.e. 0K and OT/Oz= +30 deg km-1. The pressure at Zo is 2.6~0. 13 p.e. dynes cm-2, the mass of gas above zo is 3.0 X 10-~ g cm-2, the reduced thickness 1.7 cm. The observed pressure at zo is consistent with an atmospheric model in which the pressure is 160 mb at the top of the cloud layer.