Venusian days vs. Terrestrial days: Why the Big Difference in Length?

Question

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?

Two theories. In his Alone in the Universe, Gribbin notes that whatever event gave Venus its relatively young surface occurred at about the same time as the mass extinction on Earth that ushered in the Cambrian Period. — rob, Nov 13 '16 at 02:58
Why should there be any relationship between diameter of a planet and day length? Is there any theory that predicts such a thing? — , Nov 13 '16 at 09:34
Cross-posted on earth science SE: http://earthscience.stackexchange.com/q/9097/ — David Hammen, Nov 13 '16 at 14:21
Isn't a Jovian day something like ~10-11 hours? I second @tfb in his comment. — honeste_vivere, Nov 17 '16 at 16:14
Possible duplicates: https://physics.stackexchange.com/q/7819/2451 , https://physics.stackexchange.com/q/23104/2451 and links therein. — Qmechanic, Jun 16 '18 at 01:56

score 1 · Answer 1 · answered Jun 16 '18 at 01:20

1

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.

answered Jun 16 '18 at 01:20

Natsfan

2,652

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. – rob Jun 16 '18 at 02:36

Venusian days vs. Terrestrial days: Why the Big Difference in Length?

1 Answers1