Expert: Jayendra Upadhye - 5/7/2008

Question
How long is a day, from sunrise to sunset, on Venus?

Answer
Hi,
Found your question on the question pool.
Interesting question, in the light of the fact that the planet rotates retrograde as compared to other planets.

ref:- http://en.wikipedia.org/wiki/Venus_(planet)
The para "Orbit and Rotation" clearly states ...
    "Venus rotates once every 243 days—by far the slowest rotation period of any of the major planets. A Venusian sidereal day thus lasts more than a Venusian year (243 versus 224.7 Earth days). However, the length of a solar day on Venus is significantly shorter than the sidereal day; to an observer on the surface of Venus the time from one sunrise to the next would be 116.75 days.[35] The Sun would appear to rise in the west and set in the east. ".

    However there is a twist! The same site mentions that the planet has a large axial tilt! 177deg.
    
That boils to actual 180 - 177 = @3 deg. (177deg tilt is same as 3 deg tilt excpet poles would be inverted. actually they arent, it is a way of saying the planet turns retrograde. Physically the effect is to have a reverse turning planet with 3 deg axial tilt.

If the poles were to tilt too much (like uranus), then for the pole pointing to the sun, the sun would not set for 1/2 the orbital period!
    No matter how many times the planet turned! To an observer on the planet, the sun would spiral ever higher to a zenith when the pole pinted exactly at the sun, and then spiral slowly around the horizon and out of sight when the pole would point away from the sun!

This site says it is 3 degrees in a nice table.
http://science.nasa.gov/headlines/y2000/interplanetaryseasons.html

In which case, your answer is a straightforward 116.75/2 = 58.375 hours! from sunrise to sunset. [no complicated spiral there].

Hope that suffices.
Please do rate the answer if you find it interesting.
Jayen