The Equatorial and Polar Limb-Darkening of Venus in the 8–20 μm Region

The spectral dependence of limb-darkening of Venus in the 8–20 μm region has been measured for both the equatorial and polar directions. It is shown that the magnitude and spectral variation of the polar darkening are, in general, greater than the equatorial darkening. The equatorial darkening, in fact, appears to be nearly spectrally invariant in this wavelength region, at least for the portion of the disk covered by the observations. The magnitude of the equatorial darkening is consistent with a temperature lapse rate of roughly 3 K km^(−1), assuming a model in which aerosol is distributed exponentially and mixed homogeneously with atmospheric gas.