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Venusian day [Q&A]


Vibha of Poornaprajna PU College asks, why is the Venusian day longer than its year?

Venus takes ≈225 days to revolve around the Sun, but takes ≈243 days to rotate around its axis. What is more, it rotates backwards, along an axis that is opposite to the orbital rotation axis, so compared to North as would be defined on Earth, the Sun rises in the West and sets in the East. (Not that you would be able to see it from the surface.) This causes the actual day on the planet, that is, the duration between sunrise and sunset, to be ≈60 days. See this very nice wikipedia illustration of how that occurs — NASA_SP-3029_Figure_13-1.tiff

The slow retrograde rotation has not yet been explained. It seems likely that a large scale dynamical event early in its history was the cause, though what that event was is hard to establish.

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