Phase coverage of Venus during the 1975 apparition: Diurnal variations in equatorial infrared brightness

Day-night contrasts in the equatorial infrared (8- to 14-ωm) flux from Venus were observed in digital images obtained during the 1975 apparition. A systematic increase in 8- to 14-ωm flux associated with the emergence of the atmosphere from daylight into evening was observed and is shown to exhibit significant day-to-day variability. The data also show that the daytime side of the morning terminator is warmer than the dark side, but this night-day asymmetry is systematically smaller than the day-night brightening seen in the Venus evening.