NASA / SCIENCE PHOTO LIBRARY. NASA / SCIENCE PHOTO LIBRARY.
Pioneer Venus 2 ultraviolet image of the full disk of Venus showing the cloud markings resembling bow-like waves. The patterns rapidly rotate around the planet from east to west, completing a circle in four days. The cause for the rapid rotation of the clouds around a slowly rotating planet is unclear. The markings also rotate towards the pole, but more slowly. Pioneer Venus 2 began its orbit of the planet on December 4th 1978.
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