Infrared picture of Venus from the Pioneer Venus Orbiter, 1978.

Pioneer Venus Orbiter, launched on 20th May 1978, went into orbit around Venus in December 1978 and radar mapped 93% of the surface as well as returning over 1000 images of the Venusian clouds. This picture of one of the polar regions of Venus shows the heat emision at the infrared wavelength of 11.5 micrometres (20 times longer than visible light). It was taken during the first orbit of the spacecraft around the planet in December 1978.