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The diameters of Venus (7,520.8 miles) and Earth (7,917.5 miles) are comparable, but the disparity of the length of the day for each planet - as expressed in terrestrial hours - is enormous; a day on Venus lasts 2802 hours vs. an Earth day lasting 24 hours (it's 116.750 times that of Earth).

How can there be such a great timespan difference, when the size of the two planets is nearly the same? Does the retrograde rotation of Venus relative to all of the other planets in our solar system affect the length of its day?

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The difference is simply due to the different rotational rate of the planets. It is not known why the planets rotate at different speeds. The retrograde motion has nothing to do with the rotation rate. A day is measured as the time to make one complete rotation.

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  • $\begingroup$ Your last sentence seems to refer to the sidereal day, but most people think more naturally about the solar day. On Earth and Mars the two are not very different, but on Venus and Mercury there is some funny business. $\endgroup$ – rob Jun 16 '18 at 2:36

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