Enlarge / This bow-shaped wave forms only in the afternoon. (credit: ©Planet-C) You wouldn’t expect a toy spinning top to be rotating at precisely the same rate every time you glance at it, but you probably would expect a planet to. Yet observations of Venus over the years have come up with slightly different numbers when calculating the length of a Venusian day based on its rotation. Venus is weird enough that we have to be careful to specify what we mean by “a day.” Because Venus slowly spins clockwise as it orbits clockwise around the Sun, sunlight takes a lap around the planet faster than Venus itself does a 360.